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Limestone wetland mesocosm for recycling saline wastewater in Coastal Yucatan, Mexico

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Title:
Limestone wetland mesocosm for recycling saline wastewater in Coastal Yucatan, Mexico
Creator:
Nelson, Mark, 1947-
Place of Publication:
Gainesville FL
Publisher:
University of Florida
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Subjects / Keywords:
Cells ( jstor )
Constructed wetlands ( jstor )
Groundwater ( jstor )
Limestones ( jstor )
Phosphorus ( jstor )
Species ( jstor )
Wastewater ( jstor )
Water tables ( jstor )
Water treatment ( jstor )
Wetlands ( jstor )

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Rights Management:
Copyright Mark Nelson. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
2428287 ( ALEPH )
41092449 ( OCLC )

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LIMESTONE WETLAND MESOCOSM FOR RECYCLING SALINE
WASTEWATER IN COASTAL YUCATAN, MEXICO














By

MARK NELSON


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1998





























Copyright 1998
On Construction Blueprints pp. 55-64
(Figures 3-1 to 3-10)

By

Mark Nelson














ACKNOWLEDGMENTS


I would like to thank my dissertation committee and especially its chair, Howard

T. Odum, who was an invaluable friend, critic, catalyst and inspiration for my work in

ecological engineering. I was fortunate to have a committee of gifted teachers and

scientists whose professional fields spanned the topics covered in the research. Mark

Brown, my co-chair, gave freely of his knowledge of emergy analysis, wetland ecology

and restoration. K.R. Reddy is a master of wetland biogeochemistry and generously made

his laboratory available. Daniel Spangler is a gifted theoretical and field hydrogeologist

who helped design much of the mangrove research. Clay Montague shared his expertise

in estuarine dynamics and ecological modeling. I owe a debt to all of them for their

support, guidance and patience.

The present study would not have been possible without the generous support of

the Planetary Coral Reef Foundation, Bonsall, CA and Akumal, Q.R., Mexico. The

wetland systems have been recipients of the hard work, intelligence and care of Abigail

Ailing, Gonzalo Arcila, John Allen, Mark van Thillo, Ingrid Datica and Klaus Eiberle,

who share the vision of coral reef protection and bringing appropriate new technology to

the tropical world.

I am indebted to Richard Smith, laboratory manager, and the Water Reclamation

Facility of the University of Florida for making possible most of the water quality

analyses. Yu Wang, manager of the Biogeochemistry Laboratory, Soil & Water Sciences,









conducted the limestone/phosphorus analyses, and Biol. Edgar F. Cabrera contributed his

extensive knowledge of the plants of the Yucatan.

The Center for Wetlands supported my work with a research assistantship

and by providing a stimulating environment of creative staff and students. The Centro

Ecologico Akumal (CEA) contributed the land for the research wetland units and

financially assisted in their construction costs. Charles Shaw, staff geologist for CEA,

greatly assisted by sharing his research on the hydrogeology of the region.

Finally, I would like to thank my colleagues in the Institute of Ecotechnics

for allowing me the time to pursue this research, and for all the camaraderie and

challenge during more than two decades of wonderful ecological work. "Friendship,

honor, discipline and beauty."














TABLE OF CONTENTS
page
ACKNOWLEDGMENTS........................................................................ ...11ii

LIST OF TABLES................................................................................. viii

LIST OF FIGU RES...................................... .................. ............... ...... .... xiv

A B STRA CT ......................................... .................................... ........ ... xxii

CHAPTER 1: INTRODUCTION.................................................................. 1

Scientific Questions in Ecological Engineering of Wastewater....................... 2
Wastewater Interface Ecosystems in the Tropics............................... 2
Wastewater Interactions in Landscapes with Soil
Substrate of Limestone................................................... 3
Salty Wastewater................................................................... 4.
Using Small-Scale Mesocosm Tests to Evaluate
Regional Potentials..................................................... ...4
Problems of Fitting Water Systems to the Landscape.................................. 5
Unique Characteristics of Tropical Coastal Development.................... 5
Eutrophication Impacts on Coral Reefs.......................................... 6
Issues of Human Health........................................................ ....7
Previous Studies.............................................................................. 8
Study Sites in Yucatan........................................................................ 10
Regional Study Area: Akumal Coastline....................................... 10
Growth and Development in the Yucatan...................................... 13
Sites of Mesocosm Tests........................................................ 19
Receiving Wetland............................................................. 19
C oncepts........................................... .......... ............................. .. 24
Aggregated Conceptual Model.................................................. 24
Diversity vs. Trophic Conditions in the Interface
Treatment System........................................................ 26
Ecological Succession in the Treatment Systems .............................27
Major Objectives of the Research........................................................ 28
Plan O f Study...................................... ................................. ....... 28
Sampling and Measurement..................................................... 29
Outline of the Research Report............................................................ 30
CHAPTER 2: METHODS...................................................................... 32
Treatment Systems......................................................................... 32


iv









page
Ecological Engineering Design................................................. 32
Procedures for Start-Up and Management.................................... 34
Seeding with Biota.............................................................. 34
Field Measurements............................................................... 35
B iodiversity............................................................. 35
Frequency..................................................................36
C over................................... ................................. .. 36
Importance value.........................................................36
Leaf area index............................................................ 36
Leaf holes................................... ........................... .... 37
Surface organic matter............................................... 37
Solar insolation........................................................ 37
Canopy closure........................................................... 38
Analytic Measurements.......................................................... 39
Total nitrogen and total phosphorus................................... 39
Biochemical oxygen demand (BOD).................................. 40
Chemical oxygen demand............................................... 40
Total suspended solids................................................... 40
Fecal coliform bacteria.................................................. 41
A lkalinity................................... ........................... .... 41
Salinity ................................................................ 41
Phosphorus Uptake by Limestone............................................... 41
Initial P content and uptake in wetlands............................... 41
Calcium/magnesium composition of
Yucatan limestone.............................................. 42
Experiments on phosphorus uptake by limestone................... 43
Water Budget of Wetland Systems............................................. 44
Economic Evaluation............................................................. 44
Emergy Evaluation............................................................... 45
Receiving Wetland............................................................. 46
B iodiversity...................................... ........................... ..... 46
Mangrove Soils................................................................ 46
H ydrogeology...................................................................... 49
Simulation model of water budgets...................................................... 49
Evaluating the Potential of Wastewater System for Coastal Zone................... 50
Emergy Evaluation............................................................. 50
Transformities.......................................................... 51
Economic Evaluation............................................................. 51
Regional Water Budget........................................................... 51
Regional Nutrient Budget........................................................ 51

CHAPTER 3: RESULTS...................................... ................................... 53

Treatment Mesocosms................................................................. 53









page
Design and Operation of the Wetland Units.................................. 53
Ecological Characteristics....................................................... 65
Patterns of biodiversity and dominance............................... 65
Comparison with natural ecosystems................................. 74
Dominance..................................................... 74
Shannon diversity index................................... 81
Plant cover............................................................. 81
Plant frequency........................................................... 88
Importance values........................................................ 93
Leaf area index..................................................... .... 100
Leaf holes.......................... ...................................... 100
Surface organic matter................................................. 110
Solar insolation....................... .................................. 112
Canopy closure.......................................................... 112
Chemical Characteristics and Uptake......................................... 117
Phosphorus.......................... .....................................117
N itrogen................................... ........................... .... 123
Biochemical oxygen demand.......................................... 128
Total suspended solids................................................. 128
Alkalinity................................................................ 137
Salinity.......................... ......................................... 137
Reduction in Coliform Bacteria................................................ 140
Phosphorus Uptake by Limestone.......................................... ..140
Ca/Mg analysis of limestone....................................... ...140
Initial and uptake phosphorus levels................ ............. 146
Experiments on limestone P uptake.............................. ...149
W ater Budget................................... ................................. 153
Economic Evaluation............................................................ 153
Emergy Evaluation............................................................... 157
Receiving Wetland Groundwater Mangroves....................................... 176
Biodiversity....................................................................... 176
M angrove Soils....................... ............... ..... ... .. .... .. .... .... ..... 176
N utrients.................................... ...................................... 180
Hydrogeology of Coastal Zone................................................. 189
Cross section................................... ................................. 189
Groundwater.......................... .................................. 189
Water quality in mangroves.................................................... 192
Total nitrogen.......................... ..................................192
Soluble reactive phosphorus............................... ......... 199
Chemical oxygen demand............................................. 199
Total suspended solids............... ............... ................... 199
Coliform bacteria....................................................... 203
Salinity ................................................................... 203
Simulation of Water in Treatment Units and Mangroves..........206


vi









pane
Regional Potential of Wastewater System............................................ 219
Definition of Coastal System.................................................. 219
Emergy Evaluation.............................................................. 219
Economic Evaluation.......................... ..................................229
W ater B udget................................................ .... .. .... .. .........230
N utrient Budget.................................................................. 234

CHAPTER 4: DISCUSSION..................................................................... 247

Contribution of Research to Science of Ecological Engineering.................. 247
Ecological Succession in the Limestone Wetland Units............................ 248
Comparisons of the Akumal Systems with other Treatment Approaches.........250
Comparisons with Temperate Latitude Interface Systems.......................... 254
Comparison of Emergy Indices of the Akumal Units............................... 256
Role of Limestone Substrate............................................................ 260
Seasonal Changes and Effect of the Dry Season..................................... 261
Treatment of Wastewater Containing Sea Salt....................................... 263
Simulation of Hydrological Extremes................................................. 264
Transpiration of Treatment Systems................................................ ..264
Maintaining Vegetative Biodiversity.................................................. 265
Impacts of Effluent Disposal on the Mangroves..................................... 266
Carrying Capacity for People Coastal Development Potential................... 267
Percent of Economy Required for Wastewater Processing......................... 268
Perspectives from Regional Simulation Model....................................... 269
Future Potentials of the Designed Treatment System................................ 276
Long-Term System Prospects........................................................... 277
Authorization Meeting in Mexico...................................................... 279
Questions for Research................................................................... 280
B iodiversity ............................. ....................... .. .... .. ... .... ... 280
Mangrove Change................................................................ 281
Useful Life of the Wetland System............................................ 281
Acceptability and Affordability by Local People........................... 281
Sum m ary................................... .................. .............................. 282

APPENDIX A WATER LEVEL DATA FOR AKUMAL................................... 284
APPENDIX B NOTES AND TABLES FOR WATER BUDGET
SIMULATION MODEL................................................................. 304
APPENDIX C COMPARISON WITH UNIVERSITY OF FLORIDA
SEWAGE TREATMENT FACILITY................................................. 314

R EFER EN C E S................................... .................. .............. ... .. ... ... .... ... 319

BIOGRAPHICAL SKETCH...................................................................... 330














TABLES
page
Table 2-1 Transformities values used in emergy evaluations in this study.................. 52

Table 3-1. Plant species in the treatment wetlands from surveys of May 1997,
December 1997 and July 1998. Total number of species as of May 1997:
68 species; as of December 1997:70 species, as of July 1998:66 species ................. 66

Table 3-2 Species list: mangrove wetland ecosystem, 8 December
1997. Species identified by Edgar Cabrera, Chetumal, Q.R................................. 78

Table 3-3 Species list of inland forest near Akumal, Q.R., 9 December
1997. Species identified by Edgar Cabrera, Chetumal, .Q.R................................ 79

Table 3-4 Shannon diversity indices for constructed wetland systems
based on May 1997, December 1997 and July 1998 surveys............................ ...82

Table 3-5. Comparison of Shannon diversity indices for constructed
wetlands vs. natural mangrove and tropical forest ecosystems of the
study area, based on December 1997 and July 1998 survey data........................... 83

Table 3-6. Relative cover in the wetland system cells, based on 0.25
sq m quadrant analysis, M ay 1997..................................................... ... ... 84

Table 3-7. Estimates of area coverage, including canopy, of dominant plants in
the wetland treatment cells, May 1997. Total area of each cell in system 1 is 25.3
square meters, and area of each cell in system 2 is 40.6 square meters............... 85

Table 3-8. Estimates of area coverage, including canopy, of dominant
plants in the wetland treatment cells, December 1997 and July 1998.
Total area of each cell in system 1 is 25.3 square meters, and area of
each cell in system 2 is 40.6 square meters.................................................. 86

Table 3-9. Frequency rankings of dominant plants in constructed
wetlands in May 1997, December 1997 and July 1998 transects............................ 89

Table 3-10. Importance value ranking of top eight species in each wetland treatment
cell, May 1997, December 1997 and July 1998 surveys. Values were computed by
adding relative species frequency and relative species cover and dividing by 2.
Maximum value is therefore 1.0, and total is 1.0 summing all species found









page
in the treatm ent cell........................................ .................... .. ..................... ... 94

Table 3-11 Measurements of leaf area index in the treatment cells of the
wetland systems, May 1997, December 1997 and July 1998. Values are
given with standard error of the mean......................................................... 101

Table 3-12 Leaf holes in the wetland treatment units, December 1997................... 106

Table 3-13 Leaf holes in the wetland treatment units, July 1998 data..................... 108

Table 3-14. Outside solar insolation levels and their reduction in the
constructed wetlands, 28 July 1998 between 1050 and 1145 AM.
Perimeter light levels are the measured insolation at locations 0.5 m inside
the wetland systems along their outside edges............................................... 113

Table 3-15. Light penetration and canopy closure in the wetland systems and
adjoining mangrove wetland, 29 July 1998. Data presented standard error
of the m ean ....................................... ... .................... ............... .... .... 115.

Table 3-16 Total phosphorus content of water samples from cenote
(groundwater well) near wetland treatment systems .................................... .. 120

Table 3-17 Total phosphorus in effluent from septic tank and discharge
effluent from wetland treatment systems and percent reduction of
phosphorus levels...................................... ........................ ....... ....121

Table 3-18. Total phosphorus content of water samples from the
treatm ent w etlands................................ ............... ............................... 122.

Table 3-19 Total nitrogen in effluent from septic tank and discharge effluent
from wetland treatment systems and percent reduction of nitrogen levels............... 126

Table 3-20 Total nitrogen content of water samples from cenote
(groundwater well) near wetland treatment systems......................................... 127

Table 3-21 Biochemical oxygen demand (BOD-5) in effluent from septic
tank and discharge effluent from wetland treatment systems and percent
reduction ............................................ ......... ..................................... 13 1

Table 3-22 Biochemical oxygen demand (BOD-5) content of water
samples from cenote (groundwater well) near wetland treatment systems............... 132

Table 3-23 Total suspended solids (TSS) concentrations and reduction in
septic tank and discharge water from the Akumal wetland treatment systems.......... 133









page
Table 3-24 Total suspended solids (TSS) concentrations in water samples
from cenote (groundwater well) near wetland treatment systems......................... 134

Table 3-25 Alkalinity in septic tanks, wetland systems and cenote........................ 138

Table 3-26 Salinity in septic tanks, wetland systems and cenote........................... 139

Table 3-27 Coliform bacteria concentrations in effluent from septic tank and
discharge effluent from wetland treatment systems and percent reduction. Data
is in units of most probable number of colonies per 100 ml (MPN/100 ml)............. 143

Table 3-28 Coliform bacteria concentrations in water samples from
cenote (groundwater well) near wetland treatment systems. Data is in units
of most probable number of colonies per 100 ml (MPN/100 ml)......................... 144

Table 3-29 Ca/Mg composition of Yucatan limestone as analyzed by inductive
coupled plasm a spectroscopy................................................................... 145

Table 3-30. Inorganic phosphorus content of limestone samples............................ 147

Table 3-31 Results from experiments on limestone uptake of phosphorus................ 150

Table 3-32. Daily water budget of wetland treatment systems, May 1997................ 154

Table 3-33. Daily water budget of wetland treatment systems, December 1997......... 155

Table 3-34 Purchased materials and services used in construction of wetland
systems, Akumal, Mexico. Costs are expressed in Mexican pesos(1996) and
converted to U.S. dollars at the rate of 7.8 peso/$, which was the exchange
rate in 1996 when systems were built.......................................................... 159

Table 3-35 Purchased materials and services used in construction of package
plant sewage treatment system, Akumal, Mexico. Costs are expressed in
Mexican pesos (1996) and converted to U.S. dollars at the rate of 7.8 peso/$,
which was the exchange rate in 1996 when systems were built........................... 160

Table 3-36 Emergy analysis of the constructed limestone sewage wetlands............. 162

Table 3-37 Emergy analysis of the package plant sewage treatment system............. 171

Table 3-38 Wet weight/dry weight of soils in mangrove receiving wetland,
D ecem ber 1997................................... ................................................ 177

Table 3-39 Bulk density of soils in mangrove receiving wetland, December 1997......178









page
Table 3-40 Organic matter content of soils in mangrove receiving wetland
estimated from loss on ignition and mean values of the five soil samples
from D ecem ber 1997............................................................................ 179

Table 3-41 Calcium and magnesium content of mangrove soil ash after combustion
for organic content. Results determined by inductive coupled plasma spectroscopy... 181

Table 3-42 Total Kejdahl nitrogen content of soils in mangrove receiving
wetland on 12 December 1997 before discharge of treated effluent...................... 185

Table 3-43 Total Kejdahl nitrogen content of soils in mangrove receiving
wetland before discharge (30 April 1998) and 2 months (3 July 1998),
3 months (3 August 1998) and 4 months (2 September 1998) after
discharge of treated effluent began 3 May 1998........................................... ..186

Table 3-44 Phosphorus content of soils in mangrove receiving wetland
on 12 December 1997 before discharge of treated effluent................................ 187

Table 3-45 Phosphorus content of soils in mangrove receiving wetland
before and after discharge began 3 May 1998............................................. ..188

Table 3-46 Total nitrogen in water of mangroves before and after discharge
of treated w astew ater............................................................................ 198

Table 3-47 Soluble reactive phosphorus (SRP) in water of mangroves
before and after discharge of treated wastewater.......................................... 200

Table 3-48 Chemical oxygen demand (COD) in water of mangrove receiving
wetland before and after discharge of treated wastewater ............................... ..201

Table 3-49 Total suspended solids (TSS) in water of mangroves
before and after discharge of treated wastewater............................................ 202

Table 3-50 Coliform bacteria in water of mangroves in 1998 after
discharge of treated effl uent.................................................................... 204

Table 3-51. Salinity in mangrove water in December 1997 before
discharge of sewage effluent................................... ................................. 205

Table 3-52 Salinity in mangroves in 1998. Discharge of treated
effl uent began M ay 1998...................................... .................................. 207

Table 3-53 Computer program in BASIC for simulation model of water
budget in treatm ent wetland nit.................... ................... .... .. .... .. .... ......... 210









page
Table 3-54 Spreadsheet for calculation of coefficients in water budget
simulation model of treatment units and mangroves........................................ 212

Table 3-55 Emergy evaluation table of one square kilometer of developed
coastline, Akumal, Mexico (see Figure 3-58).............................................. ..221

Table 3-56 Emergy indices for evaluating one square kilometer of
developed coastline, Akumal, M exico......................................................... 227

Table 3-57 Water budget of a square kilometer of coastline around
research site without use of wetland treatment systems.................................... 231

Table 3-58 Comparative additions to groundwater (GW) of nitrogen,
phosphorus, BOD (organic compounds) and fecal coliform in a 1-square-
kilometer area of study site with and without the use of wetland
treatm ent system s................................... .............................................. 235

Table 3-59 Phosphorus budget of a developed square kilometer of
coastline, Akumal, Mexico, with no sewage treatment and changes if
wetland system s are installed....................... .................... .. .... ... .. ... .... ....... 237

Table 3-60 Nitrogen budget of a developed square kilometer of
coastline, Akumal, Mexico, with no sewage treatment and changes if
wetland system s are installed................................... ................................. 240

Table 3-61 Organic compounds (BOD) budget of a developed square
kilometer of coastline, Akumal, Mexico, with no sewage treatment and
changes if wetland systems are installed...................................................... 243

Table 3-62 Coliform bacteria budget of a developed square kilometer of
coastline, Akumal, Mexico, with no sewage treatment and changes if
wetland system s are installed................................................................... 245

Table 4-1 Comparison of loading rates and removal efficiency of Akumal
treatment wetland units with average North American surface and subsurface
flow wetlands (Kadlec and Knight, 1996).................................................... 255

Table 4-2. Comparison of emergy indices for Akumal treatment units,
package plant at Akumal and the University of Florida wastewater
treatment system (compiled from data in Tables 3-36, 3-38 and Appendix)............257

Table 4-3 Program in BASIC for simulation model of interactions between
natural environment and human economy along the Yucatan coast..................... 273









page
Table B-I. Average monthly rainfall at Tulum, 20 km south of study site............... 308

Table B-2 Measured evaporation at Tulum, 20 km south of study site
along the Yucatan coast. Actual evapotranspiration is estimated at 900 mm
for the Yucatan. The last column is a calculation of evapotranspiration
based on the percentage of yearly evaporation that occurs in each month............... 309

Table B-3 Average monthly relative humidity, temperature, and air
vapor pressure calculated for the given temperature and relative humidity
for the Y ucatan coast................................ ............................................ 310

Table B-4 Average wind velocity, measured at Puerto Moreles, Mexico,
80 km north of study site............................. .......................................... 311

Table B-5 Estimates of monthly groundwater flow based on data from
Back (1985) and average monthly rainfall in the Yucatan.................................. 312

Table B-6 Net primary productivity in mangrove ecosystems.............................. 313

Table C-1. Emergy analysis of the University of Florida sewage
treatm ent facility................................... .............................................. 316














FIGURES
pEge
Figure 1-1 Map of eastern Yucatan Peninsula of Mexico showing coastal
area of study around Akumal, Quintana Roo, north of Tulum.............................. 11

Figure 1-2 Geological cross-section in study area showing flow and mixing
of fresh groundwater and seawater (Shaw, in press).......................................... 12

Figure 1-3 Map of study area a) shows collapse zones and areas of ancient
bays (larger black dots) b) shows areas of groundwater discharge along the
coast and sampling points. In both diagrams modem reef is indicated by
light dots offshore (Shaw, in press) ............................................................ 14

Figure 1-4 Salinity contours in Akumal during a period of no rain.
Contours are compressed on the highly porous and permeable limestone.
At the 20% contour, mixing of saltwater and freshwater below ground
surface makes the gradients steeper (Shaw, 1997).......................................... 15

Figure 1-5 Salinity contours in Akumal area after a heavy rain. Compared
to Figure 1-4, salinity gradient is displaced inland due to dilution by rain
and groundwater flow (Shaw, 1997)..................................................... ... .. 16

Figure 1-6 Map of study area showing groundwater flow in relation to
porous limestone rock (indicated by crosses) and coliform contours from
studies conducted in May-August 1997 (Shaw, in press).................................... 17

Figure 1-7 Aerial photograph of study area, Akumal, Quintana Roo,
M exico ............................................... .............................................. 20

Figure 1-8 Study area around Akumal, Mexico showing location of the wetland
systems at "A", enlarged in Figure 1-9. Contour lines in meters. (Shaw, in press).......21

Figure 1-9 Enlarged sketch of area "A" in Figure 1-8 showing location of wetland
treatment areas and mangrove where treated effluent was discharged.
Points labeled A to E are mangrove sampling stations....................................... 22

Figure 1-10 Systems diagram showing the wetland treatment unit within
the context of the coastal zone economy and ecology........................................ 25









pwge
Figure 2-1 Schematic of wetland treatment system showing flow from
houses to septic tanks to wetlands............................................................... 33

Figure 3-1 Construction blueprint: isometric view of the wetland treatment
system .............................................. .......... ....................................... 55

Figure 3-2 Construction blueprint: isometric view of piping in the wetland
system .................................................. ........................................... .. 56

Figure 3-3 Construction blueprint: center section view of the wetland
system ............................................... ............ .................................. 57

Figure 3-4 Construction blueprint: side section showing fill materials in
the w etland system ......................................... ..................................... .. 58

Figure 3-5 Construction blueprint: control box with dimensions of the
wetland treatm ent cells...................................... ................................... .. 59

Figure 3-6 Construction blueprint: treatment cell 1 header detail of the
w etlands.............................................. ................ ......... ...................... 60

Figure 3-7 Construction blueprint: treatment cell 2 header detail of the
w etlands..................................................... ........................................ 6 1

Figure 3-8 Construction blueprint: schematic showing drainfield detail
for large wetland system s...................................................................... 62

Figure 3-9 Construction blueprint: schematic showing drainfield detail for
sm all wetland system s......................................... ................................... 63

Figure 3-10 Construction blueprint: drainfield cross-section drawing of
w etland system ............................................ ................................. ...... .. 64

Figure 3-11 Species-area curves for each of the four wetland treatment
cells, M ay 1997 data............................................................................... 70

Figure 3-12 Species-area curves for each of the four wetland treatment
cells, Decem ber 1997 data........................................................................ 71

Figure 3-13 Species-area curves for each of the four wetland treatment
cells, July 1998 data............................................................................... 72

Figure 3-14 Species-area curves for the 50.6 m2 wetland unit (system 1)
and the 81.2 m2 wetland (system 2), May 1997. Transects counted 482









pAge
individuals in each system ....................................................................... 73

Figure 3-15 Species-area curves for the 50.6 m2 Yucatan wetland

(system 1) and the 81.2 m2 wetland (system 2), December 1997. Transects
counted 500 individuals in each system........................................................ 75

Figure 3-16 Species-area curves for the 50.6 m2 Yucatan wetland
(system 1) and the 81.2 m2 wetland (system 2), July 1998. Transects
counted 500 individuals in each system........................................................ 76
Figure 3-17 Comparison of species richness between treatment wetlands,
mangrove wetland and forest ecosystems, December 1997. Transects were
1000 individuals from each system .............................................................. 77

Figure 3-18 Comparison of species richness between mangrove, forest and
each treatment wetland. Transects counted 1000 individuals in mangrove
and forest, and 500 each in wetland systems 1 and 2......................................... 80

Figure 3-19 Plant species in rank sequence of importance value (IV) in
the four wetland treatment cells, May 1997 data. Importance value =
(frequency + cover)/2.......................... .................. .... .... ..... .... .. .... ... ...... .. 97.

Figure 3-20 Plant species in rank sequence of importance value (IV) in
the four wetland treatment cells, December 1997 data. Importance
value = (frequency + cover)/2................................................................ 98

Figure 3-21 Plant species in rank sequence of importance value (IV) in
the four wetland treatment cells, July 1998 data. Importance value =
(frequency + cover)/2......................................... ................................. .... 99

Figure 3-22 Photograph of wetland systems in Akumal shortly after
planting, August 1996. System 1 is in foreground and System 2 in
background, in front of edge of mangrove wetland.......................................... 102

Figure 3-23 Photograph of vegetation in wetland system 1, May 1997.................... 103

Figure 3-24 Photograph of vegetation in wetland system 1, December 1997............. 104

Figure 3-25 Photograph of vegetation in wetland system 1, July 1998..................... 105

Figure 3-26 Surface organic matter in the wetland treatment cells. Data
presented are those of initial mulching (August 1996) and surface organic
matter (July 1998) after 23 months of operation. Bars are standard errors............ 111









page
Figure 3-27 Photograph showing dense canopy cover intercepting solar
insolation, wetland system 2, July 1998...................................................... 114

Figure 3-28. An example of canopy-cover photograph using fish-eye lens,
July 1998............................................... .......................................... ... 116

Figure 3-29 Total phosphorus (TP) analyses of water samples from
wetland treatm ent system 1................................... .................................. 118

Figure 3-30 Total phosphorus (TP) analyses of water samples from
wetland treatm ent system 2................................................................... .. 119

Figure 3-31 Total nitrogen (TN) analyses of water samples from wetland
treatm ent system 1................................... ............... ............................. 124

Figure 3-32 Total nitrogen (TN) analyses of water samples from wetland
treatm ent system 2......................................... ................................... ... 125

Figure 3-33 Biochemical oxygen demand (BODs) in wetland system 1
w ater sam ples...................................... .................. ............................. 129

Figure 3-34 Biochemical oxygen demand (BOD5) in wetland system 2
w ater sam ples............................................ ......................................... 130

Figure 3-35 Total suspended solids (TSS) in water samples from wetland
system 1 ............................................... .......................................... ... 135

Figure 3-36 Total suspended solids (TSS) in water samples from wetland
system 2............................................... ........................................ ... 136

Figure 3-37 Fecal coliform bacteria in water samples from wetland
system 1. Data plotted on log scale, and units are most probable number
(MPN) of bacterial colonies per 100 ml...................................................... 141

Figure 3-38 Fecal coliform in water samples from wetland system 2.
Data plotted on log scale, and units are most probable number (MPN) of
bacterial colonies per 100 m l..................................................................142

Figure 3-39 Estimates of monthly flows of phosphorus during first year of
wetland treatment system operations (1997). Data from both wetland
system s are com bined................................ ...................... .... .. .... .. ... ..... .. 148

Figure 3-40 Graphs with results of experiments on limestone uptake of
phosphorus........................................... .................... ......................... 152










page
Figure 3-41 Diagram of emergy and money flows in wetland treatment
systems, Akumal, Mexico. Units of diagram are E15 sej/yr................................ 172

Figure 3-42 Diagram of emergy and money flows in the package plant
sewage treatment system, Akumal, Mexico. Units of diagram are
E l5 sej/yr............................................... ...................................... .... 180

Figure 3-43 Howard T. Odum inspecting root penetration and peat depth
in mangroves, Akumal, December 1997...................................................... 182

Figure 3-44 Thickness of mangrove peat in the receiving wetland around the outfall
pipe discharging effluent, December 1997. See Figures 1-9 for location of mangrove
discharge point in Akumal. Mangrove soil samples were collected 1,3, 5 and 10 m
from discharge point in N,S,E and W directions (Tables 3-43 and 3-45). Water
samples were collected at Im upstream (A), Im (B) 3m (C) and 6m (D)
downstream and 15m (E) SE of discharge point (see Figure 1-10)....................... 183

Figure 3-45 Systems diagram of the mangrove wetland receiving treated
effl uent.................................................. ........................................... 190

Figure 3-46 Potentiometric measurements of groundwater level in
mangroves, December, 1997. Piezometers were located at AB, and C.
Survey transit level was located at point D. Flowlines calculated from
data are approximately in easterly direction.................................................. 191

Figure 3-47 Chart recorder water levels in cenote near wetland systems,
27-28 M ay 1997................................... ............................................... 193

Figure 3-48 Chart recorder water levels at Yal-ku lagoon, showing tidal
record, 27-28 M ay 1997............................. ........................................... 194

Figure 3-49 Chart recorder water levels in mangrove receiving wetland,
9-14 D ecem ber 1997................................ ............................................. 195

Figure 3-50 Chart recorder water levels in cenote near wetland systems,
10-14 D ecem ber 1997............................................................ .... ... 196

Figure 3-51 Chart recorder water levels at Yal-ku lagoon, showing tidal
record, 10-14 December 1997.......................... ........................................ 197

Figure 3-52 Systems diagram for simulation model of water budgets of
treatment unit and receiving wetland showing difference equations..................... 208









page
Figure 3-53 Systems diagram showing steady state storage and pathway
flows for water budget simulation model of treatment units and mangroves............ 209

Figure 3-54 Computer simulation of the water budgets of treatment
units and m angroves................................ ............................................. 215

Figure 3-55 Simulation of water budget for wetland treatment unit and
mangroves with increase of wastewater loading (10 times higher).
Scale: sunlight 5000 Kcal/m2/day, biomass 20 kg/m2, water levels 1.5 m,
w ater inflow s Im /day............................................................................ 216

Figure 3-56 Simulation of water budget for wetland treatment unit and
mangroves with loss of groundwater inflow. Scale: sunlight 5000
Kcal/m2/day, biomass 20 kg/m2, water levels 1.5 m, water inflows
Im /day ......................................... .................. .................................. 2 17

Figure 3-57 Simulation of water budget for wetland treatment unit and
mangroves with hurricane event at year 5. Scale: sunlight 5000 Kcal/m2/day,
biomass 20 kg/m2, water levels 1.5 m, water inflows lm/day............................ 218

Figure 3-58 Map of Akumal, Mexico showing the 1-square-kilometer
coastal study area................................... ..............................................220

Figure 3-59 Systems diagram of the square kilometer coastal economy and
environment, labeled with emergy flows in El18 sej/yr from Table 3-57................ 226

Figure 3-60 Diagram of emergy and money flows in the 1-square-kilometer
coastal area, Akumal, Mexico. Units of diagram are expressed
in E18 sej (solar emergyjoules)/yr............................................................ 228

Figure 3-61 Diagram of water budget of one square kilometer of
developed coastline, Akumal, Mexico. Figures in parentheses show changes
in budget if all sewage is treated by constructed limestone wetlands.................. 233

Figure 3-62 Diagram of phosphorus budget of one square kilometer of
developed coastline, Akumal, Mexico. Figures in parentheses show changes
in budget if all sewage is treated by constructed limestone wetlands and
receiving w etlands................................ ............................................... 239

Figure 3-63 Diagram of nitrogen budget of one square kilometer of
developed coastline, Akumal, Mexico. Figures in parentheses show
changes in budget if all sewage is treated by constructed limestone
wetlands and receiving wetlands............................................................. 242









page
Figure 3-64 Diagram of organic matter (BOD) budget of one square
kilometer of developed coastline, Akumal, Mexico. Figures in parentheses
show changes in budget if all sewage is treated by constructed limestone
wetlands and receiving wetlands............................................................... 244

Figure 3-65 Diagram of coliform bacteria budget of one square kilometer
of developed coastline, Akumal, Mexico. Figures in parentheses show
changes in budget if all sewage is treated by constructed limestone
wetlands and receiving wetlands.............................................................. 246

Figure 4-1. Diagram showing annual emdollar contributions to the
constructed wetland system in Akumal, Mexico............................................. 258

Figure 4-2. Systems diagram and difference equations used for simulation
model of the interactions between the natural environment and the human
economy along the Yucatan coastline......................................................... 270

Figure 4-3. Systems diagram for Yucatan coastal model. Values shown
are steady-state storage and flows between components ............................... ..271

Figure 4-4 Computer simulation of the Yucatan coastal model. The
legend gives the full scale values of the ordinate for each quantity...................272

Figure 4-5 Simulation runs of the interaction of the environment and human
economy in the Yucatan. a/Impact of starting with nitrogen at ten times higher
value b/Impact of starting with coral at zero c/ Impact of starting with money
and assets at 1/10 value................................ .......................................... 275

Figure A-1 Water level record for cenote near wetland treatment unit,
27-28 M ay 1997................................... ............... ............................... 285.

Figure A-2 Water level record for cenote near wetland treatment unit,
28-29 M ay 1997................................... .................. ............................. 286

Figure A-3 Water level record for cenote near wetland treatment unit,
29-30 M ay 1997................................... ............................................... 287

Figure A-4 Water level record for cenote near wetland treatment unit,
30-31 M ay 1997................................... ............................................... 288

Figure A-5 Water level record of tidal heights at Yal-Ku Lagoon, 27-28 May 1997... 289.

Figure A-6 Water level record of tidal heights at Yal-Ku Lagoon,
13-16 D ecem ber 1997...................................................... ....................... 290









page
Figure A-7 Water level record of tidal heights at Yal-Ku Lagoon,
16-17 D ecem ber 1997.............................................. .. .... .. .... ... .. ... ... ....... 291

Figure A-8 Water level record of tidal heights at Yal-Ku Lagoon,
17-19 D ecem ber 1997................................ ........................................... 292

Figure A-9 Water level record of tidal heights at Yal-Ku Lagoon,
19-22 Decem ber 1997................................ ........................................... 293

Figure A-10 Water level record for cenote near wetland treatment unit,
10-14 D ecem ber 1997................................ ........................................... 294

Figure A-I 1 Water level record for cenote near wetland treatment unit,
14-17 Decem ber 1997................................ ........................................... 295

Figure A-12 Water level record for cenote near wetland treatment unit,
17-20 D ecem ber 1997................................ ........................................... 296

Figure A-1 3 Water level record for mangrove near wetland treatment unit,
9-14 Decem ber 1997............................................................................. 297

Figure A-14 Water level record for mangrove near wetland treatment unit,
14-17 Decem ber 1997...................................... ................................... .. 298

Figure A-15 Water level record for mangrove near wetland treatment unit,
17-20 D ecem ber 1997................................ ........................................... 299

Figure A-16 Water level record for mangrove near wetland treatment unit,
18-21 July 1997............................................ ................................... ... 300

Figure A-17 Water level record for mangrove near wetland treatment unit,
22-25 July 1997................................... .................. .............................. 301

Figure A-I 8 Water level record for mangrove near wetland treatment unit,.
25-28 July 1997................................... .................. .............................. 302

Figure A-19 Water level record of tidal heights at Yal-Ku Lagoon,
24 July- 1 August 1997................................ ......................................... 303














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

LIMESTONE WETLAND MESOCOSM FOR RECYCLING SALINE
WASTEWATER IN COASTAL YUCATAN, MEXICO

By

Mark Nelson

December 1998


Chairman: Howard T. Odum
Major Department: Environmental Engineering Sciences


To understand wetland self-organization and to prevent pollution of groundwater

and coral reef on the calcareous east coast of Yucatan, Mexico, a wetland mesocosm

system was developed for treatment and recycle of saline, septic-tank wastewater. High

diversity wetland ecosystems were developed in two concrete-lined chambers, using

subsurface flow through limestone gravel, arranged in series with discharge to backbeach

mangroves.

Evapotranspiration in the wetlands averaged 35% of design influent during

summer months and 20% during winter months. Tall wetland vegetation developed with

66 plant species in 131 m2. Shannon diversity of vegetation was 5.01 (logarithm base 2),

far greater than that of the mangrove wetland (1.49), but less than the inland Yucatan

forest (5.35). Leaf area index increased over 13 months from 3.96 0.28 to 6.05 0.49.









In wastewater passing through the systems, biochemical oxygen demand was reduced

85%, suspended solids 40%, phosphorus 78% and nitrogen 75%. Coliform bacteria were

reduced 99.8+%. Limestone gravel in the treatment system removed 5.75 1.68 mg/kg

phosphorus per year. Nutrients in mangrove water and soil sediments increased 5-10%

from discharge of treated wastewater. Water budgets in treatment system and mangrove

were studied with simulation model.

On a per-capita basis, the wetland systems for 40 people cost approximately $160

per person to construct, vs. over $400 for alternative treatment technologies. Operation

and maintenance costs were 10% that of conventional treatment. Emergy in purchased

inputs for construction were less than 1/3 of free environmental inputs; empower density

was 2.5 E19 sej/ha/yr (one third that of conventional treatment).

The potential for economic development using the new treatment systems was

evaluated. Treatment systems would require 0.3% of the annual monetary flow (vs. 1.1%

for conventional sewage treatment) and 2.4% of total emergy while contributing 71,000

emdollars (the monetary equivalent of useful work contributed by nature and by humans).

The new systems conserve mangroves, reduce eutrophication, prevent pollution of

groundwater, protect marine resources, and contribute aesthetic values.

Research results indicate high biodiversity can be achieved in sewage treatment

wetlands, use of limestone gravel augments phosphorus uptake and such systems can be

integrated into the larger environmental setting.














CHAPTER 1
INTRODUCTION 1

A central question in ecological engineering is how to organize the hydrological

cycle of the human economy symbiotically with that of the supporting ecosystems and

geological substrate so as to maximize their joint performance. This dissertation reports

the development and evaluation of an ecologically engineered wastewater interface

between saline municipal wastewater and a tropical coastal zone with limestone substrate,

mangrove wetlands, tourist beaches and coral reefs. Potential for this wetland system was

evaluated by estimating its role in the water, nutrient, and emerge budgets of the

emerging coastal economy.

To achieve the performance observed in ecosystems in nature, an ecologically

engineered system may need to be coupled to the geological setting and cycles as

organized with groundwater. This project uses a human-assisted self-organization

and structure to innovate a union of wastewater treatment with the larger ecosystem

context.

Ecological engineering seeks a symbiotic mix of man-made and ecological self-

design that maximizes productive work of the entire system (including the human

economy and the larger-scale environmental system). Allowing this process to self-

organize may develop better adapted ecosystems that prevail because of their greater

empower (Odum, 1991). By such minimal human manipulation and management,









materials are recycled, efficiency is enhanced, costs are reduced, and ecological

processes contribute more.

An important application of ecological engineering is the design of interface

ecosystems to handle byproducts of the human economy and to maximize the

performance of both the human economy and natural ecosystems (Mitsch and Jorgensen,

1991).

Scientific Questions in Ecological Engineering of Wastewater


Treatment and release of wastewater from coastal development in Quintana Roo,

in the Yucatan Peninsula of Mexico, involve new scientific questions..

Wastewater Interface Ecosystems in the Tropics

Tropical coastlines have dry and wet season properties, frequent hurricanes and

high temperatures year-round. There has been increasing interest in using wetlands as

interface ecosystems for wastewater treatment since early studies demonstrated their

effectiveness at removal of nutrients and suspended solids. These included use of cypress

swamps in Florida (Odum et al., 1977; Ewel and Odum, 1984) and peatlands in northern

Michigan (Kadlec, 1979).

Constructed wetlands using surface-flow or subsurface flow emergent vegetation

or aquatic plant systems have gained increasing acceptance (Hammer, 1989; Mitsch and

Gosselink, 1993; Reed et al, 1995). Since such natural or constructed wetlands are often

limited by solar insolation and show increased rates of uptake in warmer climates, such

systems may be expected to operate even more efficiently in tropical regions. In addition,

wastewater interface ecosystems may benefit from the high species diversity found in

tropical regions since diversity at the biotic and metabolic level increases the efficiency









of ecosystems (Jorgensen and Mitsch, 1991). Plant diversity may benefit wastewater

treatment by providing I/ greater variety of root systems, allowing for greater penetration

of the limestone gravel and supporting a wider range of associated microorganisms;

2/differing metabolic needs (e.g. nutrient uptake) may lead to greater capacity for

absorbing wastewater constituents; 3/differing seasonal cycles of activity which may

increase plant productivity year-round; 4/ greater ability to utilize the full spectrum of

incident solar radiation by the inclusion of shade-tolerant as well as top canopy species

and 5/ differing "specialist" capabilities (e.g. C3 and C4 photosynthetic pathways, or

quantity of aerenchyma tissue in saturated conditions) allowing for greater system

response to changing environmental conditions such as light, heat, and nutrient levels.

Greater diversity also buffers against system failure should disease or herbivory decimate

selected plant species in the constructed wetland. There is evidence that allowing self-

organization to develop cooperative mechanisms enhances the ability of adapted

ecosystems to handle pollution and toxicity (Odum, 1991).

Wastewater Interactions in Landscapes with Soil Substrate of Limestone

Landscapes on limestone platforms offer special challenges and opportunities for

ecologically engineered wastewater treatment. Calcium carbonate, the predominant

mineral compound, has the ability to react with phosphorus and thus offers the potential

for enhanced nutrient retention. On the other hand, such karstic landscapes are

characterized frequently by relatively poor or shallow soil depth. In addition, the presence

of rock such as limestone, which is dissolved by water, at ground surface permits rapid

infiltration and lateral movement of wastewater (Bogli, 1980; Milanovic, 1981).









Studies in similar subtropical and tropical limestone coastlines (e.g. the Florida

Keys and Caribbean islands such as Jamaica) have indicated that they are especially

susceptible to eutrophication through flow of septic tank effluent through porous

calcareous strata since retention time does not allow for sufficient plant uptake or

microbial decomposition (Bright et al, 1981; Pastorok and Bilyard, 1985).

Salty Wastewater

Wastewater with appreciable salt content has only rarely been studied in sewage

treatment. It is an especially important vector in ecologically engineered wetland

treatment systems as salinity is frequently a controlling factor in determining the types of

organisms that will best self-organize such systems. In addition, salinity is important in

coastal regions as groundwater salinity varies depending on factors such as tidal

interchange, rainfall and evapotranspiration. Saltwater ecosystems such as estuaries,

mangrove and salt marsh are amongst the world's most productive (Day et al, 1989).

Previous work with mangroves (Sell, 1977) and with marine ponds receiving treated

sewage have demonstrated their treatment effectiveness and capacity to self-organize to

the input of eutrophic wastewater (Odum, 1985).

Using Small-Scale Mesocosm Tests to Evaluate Regional Potentials

The two small constructed wetlands (total area 130 m2) evaluated in this research

may be viewed as a mesocosm study of the impact of such interface ecosystems if more

widely applied to the coastal regions of karstic tropical countries. A growing body of

literature has demonstrated the applicability of such mesocosm studies to evaluate

processes and potentials at higher spatial and energetic levels (Beyers and Odum, 1993).

Frequently distinctive patterns of self-organization result from interface mesocosms









exposed to extreme forcing functions such as high nutrient and hydrological subsidies

(Odum, 1991) that can then be evaluated for scaling-up and application at regional levels.

Problems of Fitting Water Systems to the Landscape


Unique Characteristics of Tropical Coastal Development

Over half the world's population live along coasts and adjoining rivers, and the

rate of population increase in coastal areas exceeds those of inland regions (NRC, 1995).

Especially in tropical developing countries, such issues have gained increasing attention

due to recent accelerated growth of tourism and land development, exploitation of natural

resources and the vulnerability of marine ecosystems, such as coral reefs, and coastal

ecosystems, such as mangrove wetlands, to the effects of pollution and eutrophication

(U.N., 1995).

At present, lack of effective and affordable means of sewage disposal is

widespread through the tropical developing world. This leads to chronic disease through

human contact with polluted water and environmental damage to sensitive ecosystems.

Coastal tourist development has been pursued by some developing tropical countries as a

method of economic progress, utilizing their resources of warm climates, beautiful

beaches and eco-tourism if they have attractive marine or terrestrial ecosystems. All too

frequently, this tourist development exacerbates the problems of water contamination by

placing large demands on available freshwater, adding new permanent and transient

populations to an area, and converting land from natural ecosystems.

Tropical areas are frequently characterized by extremely high biological diversity.

The Yucatan, because of its tropical climate and isolation, has been able to sustain to date

some of the most widespread and undamaged stands of tropical forest. The coastline









around Akumal and this portion of the eastern Yucatan coast is an important breeding

ground for loggerhead and green sea turtles, which come ashore annually to lay their

eggs.

In areas like the eastern Yucatan, the environmental hazard is especially great

because of the highly permeable karstic geology and the presence of coral reefs offshore

that are particularly sensitive to eutrophication. It is critical to not only evaluate current

development, but to develop ecologically engineered solutions. The subsurface flow

constructed wetlands, constructed as part of the present research effort in Akumal, will be

evaluated as one strategy for sustaining water quality both for people and for

environmental preservation in tropical coastal regions.

Eutrophication Impacts on Coral Reefs

Economic development results in the release of nutrients in coastal waters causing

replacement of ecosystems such as coral reefs important to tourism. The impact of

nutrients in coastal regions is greater than that of deeper waters because of the interplay

between sediments and the water column, due to the strong vertical mixing by tidal

currents and wind in the shallow water depths (Nixon and Pilson, 1983). Thus coastal

regions are unlike deeper oceanic areas where deposited materials are "lost" to surface

ecosystems. Thus coral reef ecosystems and other mature ecosystems are dependent on

internal nutrient recycling for a large portion of their gross productivity (Laws, 1983),

new growth requiring added nutrients. Nitrogen is sometimes a limiting factor for coral

reefs (D'Elia and Wiebe, 1990), normally supplied by zooplankton captured by coral

polyps. Excessive nutrients displace mature ecosystems with low diversity growths.









Thus nutrient retention by the interface ecologically engineered wastewater wetland is an

important criterion for maintenance of optimal environmental health at the higher level.

A growing body of research indicates that coral reefs and other marine

ecosystems such as seagrass can be rapidly degraded due to pollution from inadequately

treated sewage. Seagrass ecosystems are normally mesotrophic and are vulnerable to

shading, disease, and excessive epiphytic growth in eutrophied waters (Pastorok and

Bilyard, 1985). Caribbean coral reefs, despite their high gross productivity, are adapted to

oligotrophic waters where they maintain themselves using high nutrient retention and

recycling. Corals are vulnerable to sewage pollution due to the following causes:

I/ stress; 2/ decrease of available light and dissolved oxygen due to higher rates of

sedimentation and enhanced growth of phytoplantkon and other microorganisms in the

water column; 3/ overgrowth and bio-erosion of corals by fleshy macro-algae and benthic

filter-feeding invertebrates that outcompete corals in high-nutrient waters; 4/ diseases

resulting from bacterial growth stimulated by mucus-production by eutrophied corals;

and 5/ direct chemical toxic effects (Hallock and Schlager, 1986; Pastorok and Bilyard,

1985; Lapointe and Clark, 1992; and Hughes, 1994).

Issues of Human Health

Contamination of water resources is one of the leading causes of disease in

tropical countries (U.N., 1995). Coastal areas with their shallower water tables are

especially vulnerable to groundwater pollution. Water pollution includes pathogens

carried by improperly treated sewage and potentially toxic chemicals. Pathogens include

disease-causing bacteria, protozoa, viruses and helminths. Chemical hazards include









heavy metals, organic chemicals, and nitrates in sufficient concentrations to cause illness

(Krishnan and Smith, 1987).

Previous Studies


Coral reef deterioration caused by eutrophication was studied in Kaneohe Bay,

Oahu, Hawaii, which received sewage effluent from a treatment plant. In parts of the bay,

coral loss stemmed from a buildup of organic matter, causing anaerobic conditions that

released hydrogen sulfide, overgrowth from the explosive growth of "green bubbly

algae" (Dictosphaeria cavernosa), sedimentation, and loss of light and competition by

filter-feeders in increasingly turbid waters (DiSalvo, 1969; Laws, 1983; Grigg and

Dollar; 1990). There was a proliferation of filter-feeders that bore into the corals. Benthic

organisms outcompete water column plankton and filter-feeders in oligotrophic waters,

but the reverse is true in nutrient-rich conditions (Laws, 1983).

Previous studies of subsurface flow wetlands for sewage treatment have

demonstrated their advantages in situations of small, on-site sewage loading in areas

where land is scarce, or in situations where avoidance of malodor and mosquito-breeding

are important (Kadlec and Knight, 1996). These are all the case in Akumal because of the

high visibility of the treatment site, the need to create a nuisance-free and aesthetically

attractive system, and the potential of a well-designed subsurface flow wetland of

providing an inexpensive but highly effective degree of sewage treatment. As is the case

in the U.S. and Europe where this approach is rapidly spreading, the advantages of

constructed wetlands are that, because they rely on more natural methods, they are less

expensive to build and operate than conventional sewage treatment plants

(Tchonbanoglous, 1991). Constructed wetlands also can produce a standard of treatment









equivalent to tertiary or advanced wastewater treatment. This is far better than a typical

"package plant" or municipal sewage plant that produces effluent at secondary sewage

standards quality, requires high capital investment and technical expertise and is energy-

intensive (Reed et al, 1995). Subsurface wetlands use little or no electricity and

technology and require little technical supervision once installed (Cooper, 1992, Steiner

and Freeman, 1989; Green and Upton, 1992; Steiner, 1992). However, there is little prior

research with these systems in tropical, karstic, coastal conditions.

Wetland systems have long hydraulic residence times and through a variety of

mechanisms (sedimentation, antibiotics, filtration, natural die-off etc.) have shown

promise in achieving large reductions in coliform bacteria without the use of disinfectants

like chlorine used in conventional sewage treatment (Reed et al., 1995). Chlorine has the

potential to form toxic byproducts, such as chloramine, when released into marine

environments (Berg, 1975). Bacteria can break down chlorinated hydrocarbons into

compounds that may be far more dangerous than the original ones (Gunnerson, 1988),

and sometimes de-chlorination has been required by regulatory agencies, further adding

to the expense of such approaches (Kott, 1975).

The dynamics of limestone in subsurface flow wetlands is also largely unknown.

Theory suggests that limestone should increase phosphorus retention since calcium and

magnesium are the primary agents of phosphorus fixation in alkaline conditions (Reddy,

1997). A previous study with subsurface flow wetlands in Canada examined the efficacy

of dolomite [CaMg (C03)2] substrate containing 55% CaCO3. The substrate was found to

be effective at removal of P in influent wastewater handling secondary wastewater, but

when primary wastewater with higher P levels were used, P retention capacity proved









inadequate, and P-retention capacity decreased by 77% over 45 months of operation

(Reddy, 1997).

Study Sites in the Yucatan


Regional Study Area: Akumal Coastline

The research site is the coastal region around Akumal, Quintana Roo, Mexico

(Figure 1-1), about 90 kilometers south of Cancun on the eastern coast of the Yucatan

Peninsula, and 10 km north of the town and Mayan ruins at Tulum. Like many tropical

coastlines, the eastern Yucatan is underlain by permeable limestone that, in a kilometer-

wide area adjacent to the coast, is believed to be the remains of Pleistocene coral reef

communities (Shaw, in press). The hydrogeology of the coastal region around our study

site in Mexico was studied during the 1960s and 1970s (Ward and Weidie, 1976; Ward et

al, 1985), and water budgets for the region were developed by Lesser (1976).

In the northern third of the Yucatan (which includes the study site at Akumal),

maximum elevation is about 40 m though most of the land surface is in a very flat plain

of rough, pitted terrain, caused by weathering of the very permeable limestone, which is

exposed over most of the surface. Because of the general absence of other sediments or

soil, no surface drainage system exists. Cenotes (sinkholes) are the main bodies of fresh

water, and almost all water movement is subsurface through the fractured limestone.

Shaw (in press) has described the area's geologic profile and how the modern

topographic features have been derived from their Pleistocene predecessors (Figure 1-2).

About one kilometer inland is an Upper Pleistocene (Sangamon) beach ridge, with a

maximum elevation of 8 m, which is segmented by triangular spits that extend up to 750

m towards the sea. Modem, sandy, rounded bays have been formed by Holocene flooding



















































Figure 1-1 Map of eastern Yucatan Peninsula of Mexico showing coastal area of study
around Akumal, Quintana Roo, north of Tulum.













Ancient beach


Younger limestone belt '


Lagoon
Mangrove
and Karst Zone


Core holes Brackish water exits
_.. Brackish water ,.. _


Older limestone


Freshwater


Sea water enters


Figure 1-2 Geological cross-section in study area showing flow and mixing of fresh
groundwater and seawater (Shaw, inpress)









of the Pleistocene ones. Behind the headlands several hundred meters is a mixing zone

where the mix of fresh and saltwater have led to dissolution of limestone, the collapse

creating lagoons such as Yal-Ku in Akumal (Figure 1-3). While this collapse has been

attributed solely to the CaCO3 solution kinetics in the mixing zone (Back et al, 1979),

this area is associated with mangrove wetlands and biological activity may have been at

least partly responsible for the limestone dissolution (Odum, pers. comm.).

Akumal, which attracts tourists for its beaches, diving and snorkeling, has

experienced growth, from dozens of permanent residents in 1970 to around 500 currently,

with yearly tourist stays in the tens of thousands of days. There is evidence, from water

quality monitoring done by the Centro Ecologico Akumal (CEA), that there is growing

pollution of the terrestrial and marine environments. Shaw (1997) has documented a

pollution plume in Akumal as high as 2000 coliform colonies/100 ml in groundwater.

The finding of pollution correlates with the movement of this water through reef rock of

high porosity and permeability (Figures 1-4, 1-5, 1-6).

This pollution poses dangers both for people, due to contamination of

groundwater supplies and recreational contact with improperly treated sewage, and for

natural ecosystems such as the coral reef system offshore. Pollution and beach

development also are of concern in the study area because the coastline around Akumal is

an important breeding ground for leatherback and green sea turtles, which come ashore

annually to lay their eggs.

Growth and Development in the Yucatan

The rapid growth of the Yucatan Peninsula as an international and Mexican

tourist destination followed the selection of the area by the national government because












YalKu'
Lagoon
Half Moon
Bay

Akumal Bay


Figure 1-3 Map of study area a) shows collapse zones and areas of ancient bays (larger
black dots) b) shows areas of groundwater discharge along the coast and sampling points.
In both diagrams modem reef is indicated by light dots offshore (Shaw, 1997)









































Figure 1-4 Salinity contours in Akumal during a period of no rain. Contours are
compressed on the highly porous and permeable limestone. At the 20% contour, mixing
of saltwater and freshwater below ground surface makes the gradients steeper (Shaw, 1997).











Salinity, % SW
May 16, 1995


storm surge


Yal Ku Lagoon


Figure 1-5 Salinity contours in Akumal area after a heavy rain. Compared to Figure 1-4,
salinity gradient is displaced inland due to dilution by rain and groundwater flow (Shaw,
1997)





































Figure 1-6 Map ofstudy area showing groundwater flow in relation to porous limestone
rock (indicated by crosses) and coliform contours from studies conducted in May-August
1997 (Shaw, 1997)









of its excellent beaches, beautiful off-shore coral reefs, and Mayan ruins. Cancun now

receives over two million visitors per year and Quintana Roo close to three million

annually. The entire population of the state of Quintana Roo was less than 25,000 in

1950, but grew to around 200,000 by 1980 (Edwards, 1986). Evidence from tourism

development in other countries indicates that intensity of negative environmental and

cultural impact are related to scale (Jenkins, 1982, Rodenburg, 1980).

The geology of the coastal area of the eastern Yucatan is one of extreme

topographic flatness, underlain with carbonate rocks, predominantly limestone, of

Tertiary age. The soil is generally shallow (0-20 cm deep), which, coupled with high

permeability of the limestone, results in rapid infiltration of rain and high lateral

movement. The result is a thin lens of groundwater (less than 70 m thick) overlying

deeper groundwater that is close to the salinity of ocean water (Hanshaw and Back,

1980).

The Yucatan region is freshwater limited despite the ample rainfall (around 1100

mm of annual rainfall) and humid climate, and strategies for effective water utilization

have characterized human settlement in the region since the time of the Mayan

civilization (Back, 1995). These water limitations result from the nature of its almost pure

limestone karstic geology without appreciable other sediments. When the limestone

dissolves, forming solution depressions, these channels are not filled, so retain high

permeability and porosity. This geology produces low hydraulic head, which results in

restricted freshwater aquifers since the freshwater/saltwater interface is quite close to the

ground surface near to the coast. The Yucatan also lacks rivers, except in its southern

portions, because with the nearly flat topography of a coastal plain, and absence of









sediments, infiltration of rain to the water table is extremely rapid (Espejel, 1987).

Seasonal variability of rainfall is considerable, which also limits freshwater availability.

The region's high permeability not only decreases the amount of freshwater available, but

also makes the water supply very vulnerable to contamination by sewage effluent,

agricultural runoff, and the products of litterfall decomposition from the inland forests.

The resulting pollution, exacerbated by tropical climate, which favors the growth of

disease bacteria, is widespread in the Yucatan (Back, 1995).

Sites of Mesocosm Tests

Two subsurface flow wetlands for sewage treatment were constructed off the

"main street" in Akumal to serve residences, offices and public toilets. These constructed

wetlands are located about 250 m inland from Akumal Bay, and in close proximity (5-50

m) to a natural mangrove wetland as can be seen in an aerial photo of Akumal (Figure 1-

7), a topographic map of the study area (Figure 1-8) and sketch of treatment wetland units

and mangrove areas of the study (Figure 1-9). Groundwater was encountered at less than

1 m below ground surface during construction in August 1996. There is a thin layer of

sandy soil (6-10 inches) below which limestone rock is encountered.

Receiving Wetland

The mangrove wetlands around Akumal are unusual in that most have a groundwater

connection to seawater rather than having surface tidal channels. But like all mangrove

ecosystems, their hydrologic and salinity environments are highly dependent on the

relative and shifting predominance of freshwater and seawater that they receive.

Productivity in mangroves typically increases as one moves from mangrove areas
















24'*** ..


-U
~


= -


Figure 1-7 Aerial photograph of study area, Akumal, Quintana Roo, Mexico.


- *n M~ i


k ? '- 1 X-
& ^i4







--6
7


"L .I ... ;./ .""-. .....H. .... .." \ --.*








VScale



systems at "A", enlarged in Figure 1-9. Contour lines in meters. (Shaw, in press).
I,, Ullalf Moon Bay A



/ /0 100 200meters
Scale
Caribbean Sea Contour Interval- meter

Figure 1-8 Study area around Akumal, Mexico showing location of the wetland
systems at "A", enlarged in Figure 1-9. Contour lines in meters. (Shaw, in press.).










zN


Edge of
Mangrove


Ccnotec


Discharge point
N


Wetland System I


mangrove


Mangrove


Wetland System 2


10m


Sampling points A,B,C, D and E



Figure 1-9 Enlarged sketch of area "A" in Figure 1-8 showing location of wetland
treatment areasmangrove where treated effluent was discharged. Points labeled
A to E are mangrove sampling stations.









dominated by low-nutrient and high salinity seawater to ones enriched by freshwater

nutrient inputs and with decreased salinity (Day et al., 1989).

Mangroves have been shown to be effective in treating secondary wastewater. Sell

(1977) studied two South Florida tidal mangrove ecosystems enriched by effluent from a

sewage treatment plant. Mangrove growth was enhanced and there were no significant

differences in species composition, seedling survival or litterfall between mangroves

areas receiving enriched nutrient waters and control mangrove ecosystems.

Soils in the Akumal region are characterized by low nutrient status. Noguez-Galvez

(1991) studied nutrient levels near Carillo Puerto (19deg 16'N., 88 deg. 07' W) about 50

km inland from the coast and 75 km south of Akumal after differing ages of fallow

following slash-and-bum shifting agricultural use. Total N in the 0-5 cm layer was 0.437

0.022% at 1 year fallow rising to 0.619 0.095% after 20 years fallow. In the 6-11cm

layer, the total nitrogen data were 0.316% 0.044% after 1 year, and 0.478 0.076%

after 20 years. Phosphate levels were 12.16 1.75 mg/kg after 1 year in the 0-5 cm level,

rising to 16.72 4.61 mg/kg after 10 yrs, and 6.35 2.35 mg/kg in the 6-11 cm level after

1 year, and 11.33 7.7 mg/kg after 10 years of fallow.

At Puerto Moreles, Mexico, about 70 km north of the study site, Feller (1998)

found autochtonous mangroves without external source of sediment, creating a highly

organic peat substrate in the saturated subsurface. These soils are classified as solonchaks

and histosols in view of their high organic content and salinity (McKee, 1998). The

overall environment is oligotrophic and dominated by calcium carbonate limestone.

Human impacts include road-making, clearing, diking, filling, and garbage dumping

associated with tourist development. Road impoundments have not severed hydrological









connections since drainage is predominantly through groundwater connection with both

fresh and saltwater. Trejo-Torres et al (1993) found that Yucatan coastal mangroves

export freshwater during the rainy season and receive considerable seawater during drier

periods. In Belize, south of the study site, mangroves were primarily phosphorus limited,

and fertilization with phosphorus or a combination of nitrogen, phosphorus and

potassium (but not with nitrogen alone) produced sizeable increase of growth in

mangrove species (Feller, 1995).

Mangroves were found in five zones along the Yucatan coast depending on

distance from the coast. Highest biomass and basal areas were found in the mangrove

zone closest to the coast (Feller, 1998), which is the zone receiving the experimental

discharge of treated sewage effluent at Akumal.

Concepts


Aggregated Conceptual Model

Figure 1-10 is an aggregated systems diagram of the treatment unit within the

context of the coastal economy and environment. The sources of natural energy include

sun, wind, rain, inland groundwater flow, and wave and tidal activity of the sea.

Primary producing ecosystems are the inland forest, the mixed wetlands shaped by both

freshwater and saltwater near the coast, and the marine ecosystems (seagrass, coral reef

etc.). The human economy is supported by these natural ecosystems, local resources

(limestone, forest products), and imported goods and services. Tourism is the principal

source of monetary flow in the area; it pays for goods and services. The treatment

wetland units make an interface between the wastewater produced by the human






















upland forest / I idd \ \


\/ \f, salt \ nutri nt
\ -^ ^\ H20> \ 1 -- H20
-treatment
mixed units
/ wetlands


Akumal coastal zone
Quintana Roo, Mexico



Figure 1-10 Systems diagram showing the wetland treatment unit within the context of the
coastal zone economy and ecology.









economy before discharging treated water and nutrients to be recycled back into the

mixed wetlands.

Diversity vs. Trophic Conditions in the Interface Treatment System

These ecologically engineered systems provided an opportunity to investigate issues

of diversity vs. trophic state. Constructed wetlands have generally failed to maintain high

species numbers and diversity. This failure has been attributed to high nutrient waters

favoring the growth of species (such as Typha spp. or Phragmites spp.) that out-compete

other, less aggressive species. In the United States and Europe, many constructed

wetlands have not attempted to provide ecosystem attributes. They were designed as

monocultures or planted with only 2-3 species, but have nevertheless provided

satisfactory water treatment (Reed et al, 1995).

The relationship between nutrient status and species diversity is far from well

understood. Yount (1956 cited in Odum, 1996) correlated pulses of nutrient enrichment

with increased dominance, variation, competitive exclusion and loss or masking of rarer

species. However, natural conditions of steady-state, high eutrophication have also

promoted high diversity as contrasted to sudden conditions of eutrophication caused by

anthropogenic pollution (Odum, 1996). Some types of human disturbance (e.g. fire,

grazing and cutting in Mediterranean-climate Israel) enhance numbers of species

(Naveh and Whittaker, 1979 cited in Mooney, 1986).

Similarly, while the prevalent tendency is to regard high species diversification as

a sign of ecosystem development toward maturity (Margalef, 1968), there are other

circumstances in which high initial nutrient levels and species numbers are reduced as









storage are consumed (Odum, 1968), leading to suggestions that maximum species

numbers may be maintained at intermediate successional stages (E.P. Odum, 1993).

Ecological Succession in the Treatment System

The research presented an opportunity to study ecological succession in the

wetland mesocosms and to investigate some of the theoretical relationships posited for

such self-organization.

Odum (1994) noted that succession is the process by which structure and

processes are developed by ecosystems from available energies and resources. These

progressions often include system adaptation to physiological challenges, the building of

storage, development of diversity and interchange with the larger, external

environmental setting.

Ecological succession typically includes a period of rapid initial growth

dominated by aggressive, short-lived, pioneer species, giving way over time to species

with high biomass and gross productivity but less net production.

Among the characteristic patterns observed after system biomass and non-living

organic matter have been increased and as primary succession gives way to a more

mature, or equilibrium, stage are a greater balance between primary productivity and

respiration. As succession proceeds, the more mature ecosystem tends to display greater

internal cycling and retention of nutrients, increased specialization and mutualism, and

increase of efficiency of use of input energy (E.P. Odum, 1971).

The Akumal research offered an opportunity to track ecological succession and

self-organization from an initial state of virtually lifeless quarried limestone gravel and to









track ecosystem changes that resulted from the input of domestic wastewater to an initial

planting of wetland species.

Major Objectives of the Research


The major objectives of the present research were to develop a new, ecologically

engineered wastewater treatment system and to evaluate its effectiveness and integration

into the Yucatan coastal environment and human economy. Among the new elements

under investigation were the efficacy of utilizing limestone gravel as the primary

substrate for the constructed wetland, the ability of constructed wetlands with high-

nutrient inputs to sustain a high level of biodiversity and devising an integration with the

natural mangrove wetlands. In addition, evaluating whether the new treatment system

was economically cost-effective compared to other approaches and whether its use of

local resources (evaluated through emergy comparisons with other alternatives) would

make it more sustainable for a tropical developing country than conventional sewage

treatment options. Finally, if applied on a regional scale, to what extent would such a

system retain the anthropogenically-produced nutrients which pollute groundwater and

threaten the health of off-shore ecosystems such as coral reef?

Plan of Study


1. Two pilot sewage treatment systems were constructed using saline influent wastewater,

limestone gravel and multiple seeding of species on the eastern coast of the Yucatan.

2. The living ecosystem was evaluated as it developed tracking species, diversity indices,

percent cover, leaf area index, and transpiration estimated indirectly.









3. The water and nutrient budgets were evaluated by analysis of inflow waters and

outflow waters, and a budget and simulation model that represents the seasonal cycle and

role of the ecosystem were developed.

4. After defining a representative square kilometer of coastal zone including tourist

developments and their wastewater flows, the coastal water budget was evaluated. The

role the new wastewater systems can have in the coastal water budget if expanded to

service a kilometer of coastline was examined.

5. The share of the system contributed by the environment and the economy was

evaluated using emergy, transformity, empower and empower densities of the principal

features of the wastewater unit and the main parts of the coastal area (hotels, people,

substrate limestone, dollar circulation and exchange).

Sampling and Measurement

Periodic sampling of water quality was conducted for the septic tanks, wetland

treatment compartments, groundwater and mangrove receiving wetland. Analysis was

done in local Mexican laboratories (Alquimia, Cancun and Centro Ecologico Akumal) for

parameters such as coliform bacteria and biochemical oxygen demand (BODs), which

require immediate testing. Other parameters, such as phosphorus, nitrogen, suspended

solids, and alkalinity, were tested in laboratories at the Water Reclamation Facility,

University of Florida, Gainesville by Richard Smith, the laboratory manager.

Bulk density and water-holding capacity for soils from the mangrove receiving

wetland were conducted in the laboratory of the Centro Ecologico Akumal. Soil samples

from the mangrove receiving wetland were analyzed for organic matter content and

phosphorus and nitrogen content at the at the Institute of Food and Agricultural Sciences









(IFAS) Soil Testing Laboratory, Gainesville. Analysis for mineral composition of the soil

was conducted using X-ray diffraction techniques by Dr. Willie Harris at the Pedology

Laboratory of the University of Florida, Gainesville.

Field measurements for ecological characteristics such as species number, cover

and frequency were conducted during research visits to the study site. Identification of

species were made with Edgar F. Cabrera, a biologist from Chetumal, Quintana Roo.

Limestone from the system was collected before treatment began and after 11

months of system operation. Analysis of the limestone for elemental composition was

done at the IFAS Soils Laboratory, with the help of Dr. James Bartos. Analysis of

limestone gravel for phosphorus was done at the University of Florida Wetland

Biogeochemistry Laboratory with the help of its manager, Ms. Yu Wang. Experiments

on limestone uptake of phosphorus were conducted at the same laboratory.

Outline of the Research Report


The research was reported in the following manner. Chapter 2 gives the

methodology followed in all the components of the research. Chapter 3 presents results

from the following areas

a/ Ecological characterization of the limestone wetland ecosystem, including

species number, biodiversity, frequency, cover, leaf area index, leaf holes, interception of

sunlight, canopy closure and surface organic matter.

b/ Wastewater treatment including total phosphorus, total nitrogen, biochemical

oxygen demand, total suspended solids, salinity, alkalinity and uptake of phosphorus by

limestone gravel, and water budget.









c/ Economic and emergy evaluation of the wetland treatment system and in

comparison with an alternative conventional treatment approach.

d/ Impact on the mangrove wetland including characterization of the hydrology

and soil sediments of the ecosystem; and nutrient status of the soils and water before and

after discharge of treated wastewater effluent from the limestone wetland unit.

d/ Simulation of the water budget of wetland treatment system and mangrove.

e/ Regional evaluation of application of the treatment wetlands. This was done by

first assessing the emergy and monetary flows in a square kilometer of developed

coastline, then evaluating the impact on this larger system's water and nutrient budgets

with and without the use of the wetland treatment systems.

Chapter 4 presents a discussion of the major findings of the present study, and

commentary on important vectors in the new wetland system for treating domestic

wastewater along the Yucatan coast. Observations are presented on the pattern of

ecological succession, the role of limestone, and a simulation model is developed for the

interaction of the environment and the tourist economy of the area. Finally, potential for

future application of the system in the region is discussed and remaining questions for

future research are listed.

Appendix A contains water levels measured for the tide at Akumal, in the

mangrove and in nearby cenote (groundwater well). Appendix B presents literature data

used in the model. Appendix C contains the emergy evaluation of the University of

Florida sewage treatment facility that is used for comparison to the limestone wetland

system.














CHAPTER 2
METHODS


Treatment Systems


Ecological Engineering Design


A constructed wetland for sewage treatment was developed meshing with the

environmental/geological context of the Akumal coastline. Following the concept of

ecological engineering, maximizing the work of natural elements, minimizing the use of

machinery and reducing cost. A system of contained wetlands was used to treat septic

tank discharge using gravity-flow, eliminating the need for electrical pumps (Figure 2-1).

Because of the thin soil layer, high porosity of underlying limestone and high

water table of the coastal settlements, an impermeable concrete liner prevented discharge

of wastewater before adequate treatment could be accomplished. A two-celled system

was used so that there was capacity to absorb torrential rains.

Limestone gravel with 1/4 3/8 inch diameter was used in the system. The

advantage of using smaller size gravel is that surface area and porosity is increased.

However, the trade-off is that smaller limestone gravel may undergo greater danger of

compaction and dissolution over time (Steiner and Freeman, 1989). Larger limestone

rock (2-4 inch diameter) was used in the first and last meter of each treatment cell to

minimize the danger of clogging near inlet and collector pipes.














-* -


Kitchen


Soil


Figure 2-1 Schematic of wetland treatment system showing flow from houses to septic
tanks to wetlands.


Constructed Subsurface

Wetland System









Outflows from the treatment wetlands were discharged into natural groundwater

mangrove wetlands where there was natural filtering capacity of rich, organic soils and

root uptake.

The treatment wetland systems were built with financing and support from

Planetary Coral Reef Foundation and the Centro Ecologico Akumal. Local Mayan

contractors and laborers did the construction work. Local sources of limestone

and sand were used. Public meetings in Akumal explained the planned research and

provided updates on research findings to government, business and local residents.

Procedures for Start-up and Management

An initial layer of sawdust mulch was applied to the system over the limestone,

establishing an aerobic layer for plants that could be sustained later by leaf litter drop.

Maintenance guidelines called for minimal interference without pruning

vegetation or eliminating species. Disease or pest pulses would be allowed, since these

form a part of nature's diversity mechanisms. Monitoring allowed tracking of natural

self-organization of introduced and volunteer plant species.

Seeding with Biota

The wetlands were planted with a wide variety of wetland plants, some

transplanted from local wetland areas, some from local commercial plant nurseries,

others from the botanical garden at Puerto Moreles and local gardens in Akumal. Some

species entered the system as seeds carried in by wind or animals from nearby wetlands,

as seeds or seedlings in the soil of plants transplanted from the wild, or during the

construction process.









There was no attempt to limit species. None were removed manually as unwanted

('weeds"). Trees and large palm species were planted at least 2 m away from the system

piping to minimize maintenance problems with roots. Multiple rounds of seeding were

arranged following experience with promoting self-organization in mesocosms (Beyers

and Odum, 1993).

Field Measurements

Biodiversity

Plant species richness was determined by identification of plant species in the

wetlands with the assistance of Edgar Cabrera, Chetumal, Q.R., a botanist from the

region. Transects of approximately 250 observations were conducted in each of the two

treatment cells of the two wetland systems, giving a total of about 1000 observations.

These observations were made in May 1997, December 1997 and July 1998.

Comparisons with biodiversity of natural ecosystems in the region (mangrove and

tropical inland forest) were done by conducting transects with 1000 individual plants,

identifying each to species in December 1997.

Biodiversity was calculated using the Shannon diversity index (Shannon and

Weaver, 1949; Brower et al, 1991):

H' = -1 p, log Pi

where p, = ni/N

"pi" is the proportion of species 'T' in the total number of individuals in the population

(N). The Shannon biodiversity index was calculated using the above formulas for log 2

and log 10.









Frequency

Frequency is a measure of the probability of finding an individual species with the

overall population sample (Brower et al, 1991). Plant species' frequency in the wetlands

was determined by analysis of the transects. Each individual plant stem was counted as

an observation in the transect. Data was tabulated for each treatment cell and cumulative

data were tabulated for each wetland system, and data for the combined two wetland

systems were analyzed.

Cover

Plant cover for each species was determined by 1/ use of 0.25 m2 quadrats in each

treatment cell and estimating percent cover of each species present, as well as percent of

bare ground; 2/ measuring canopy cover of the most prevalent species (15-20) in each

treatment cell (May 1997) and 3/estimating canopy coverage of all wetland species in

each treatment cell (December 1997 and July 1998).

Importance values

Importance values (IV) were calculated combining frequency and cover data and

dividing by two, so that the sum of all IV values for each system equaled one. These

calculations were made using the May 1997, December 1997 and July 1998 field data.

The graph of these data, called a dominance-density curve or species importance curve,

was plotted on a log/arithmetic scale against rank order (Brower et al, 1991).

Leaf area index

Leaf area index was determined by the point-intercept method. Approximately 50

measurements were made in each treatment cell of the wetland systems in May, 1997,









December 1997 and July 1998. Using a tall piece of steel rebar moved a set distance

along pre-assigned transect lines, the number of leaves touching the pole were recorded.

Each treatment cell had approximately 50 observations at each round of study.

Leaf holes

Holes in leaves due to herbivory, decomposition and other causes were measured

in December 1997 and July 1998 by estimating percent leaf damage and loss on 5

randomly selected leaves of each of the species present in the wetland. Then these data

were multiplied by the relative frequency of each species to give an overall measure of

leaf holes in the wetland systems.

Surface organic matter

Surface organic matter was determined by collecting surface litter from four 0.1

m2 quadrats within each cell of the two wetland systems in July 1998. Four samples of

the original woodchip/sawdust mulch from 0.1 m2 quadrats from a similarly constructed

wetland system in Akumal were collected to provide a measure of the starting surface

organic matter of the wetlands. The surface litter was dried at 70C and weighed, then

combusted at 4500C in a muffle furnace of the Water Reclamation Laboratory

of the University of Florida and reweighed. Organic matter content of samples was

determined as the difference between starting and final weights.

Solar insolation

Solar insolation and light interception in the wetland systems was measured

using a LI-COR LI-1 89 Quantum/Radiometer/Photometer equipped with a LI-COR

Terrestrial Radiation Sensor, Type SA (LI-200SA) pyranometer sensor. The pyranometer









was factory calibrated against an Eppley Precision Spectral Pyranometer under natural

daylight conditions, giving an absolute error of 5% maximum, typically 3%.

Quantum light measurement results were in pamol s- m-2 (1 nmol s-I m-2 is equivalent to

1 gEinstein s-1 m-2).

Light measurements were conducted on 28 July 28 1998, a cloudless day, from

1050 to 1145 AM. Measurements were made of ambient solar insolation outside the

wetland systems before and after measurements of each wetland cell. Approximately 30

measurements were made in each of the 2 wetland cells of wetland system 1 and 50

measurements in each cell of wetland system 2. Measurements were made 0.5 m in from

the edge of each cell and then every 1 m across the cells.

Canopy closure

Canopy closure in the wetland systems was evaluated in July 1998 using

analysis of hemispheric canopy photography (Rich, 1989). Photographic images of the

wetland canopies were made using a 180 fish-eye lens adapter on a Nikon camera. Nine

photos were taken at predetermined and equivalent locations in each of the wetland cells,

and in the discharge area of the mangrove ecosystem, then digitized and converted to a

gray scale using Photoshop 2.0. Analysis for amount of canopy and light penetration was

done with MapFactory software.









Analytic Measurements

Total nitrogen and total phosphorus

To determine nutrient treatment in the wetlands of phosphorus and nitrogen,

laboratory tests for total phosphorus and total nitrogen were conducted on wastewater

samples from the wetland treatment systems.

Phosphorus was determined using persulfate digestion followed by the ascorbic

acid method, SM 4500-P (APHA, 1995). Tests were conducted at the University of

Florida Water Reclamation Laboratory. Total nitrogen was determined using the

persulfate method, SM 4500-N (APHA, 1995).

Samples were collected from the septic tank, from the standpipe at the end of cell

1 and cell 2 in each wetland treatment system. A sample was collected from a cenote

(shallow groundwater well) with water accessible a few feet below ground level located

just a few meters from the wetland treatment system. This cenote is located on the inland

side of the wetland systems, and is presumed to give some indication of local

groundwater background levels. After collection in a 10 ml sample bottle, 1-2 drops of

concentrated sulfuric acid was added to preserve the samples until shipping to the

laboratory.

To determine variability in the total P and total N laboratory test, two samples

were run three times in August and September, 1997 so that standard deviation and

standard error of the mean could be determined.









Biochemical oxygen demand (BOD)

Biochemical oxygen demand (BOD) was determined using EPA method 405.1

(EPA, 1993). This is a five day test with sample kept at 20C. Samples (250 ml) were

collected as described above and kept cool during transport to the laboratory. The

materials were tested in laboratories in Cancun. The tests from January to April 1997

were conducted at Laboratorio Alquimia, Cancun and those from May 1997 were

conducted at the laboratory of Jose Castro in Cancun. Both are certified laboratories for

water analysis.

Chemical oxygen demand (COD)

Chemical oxygen demand in the water of the mangroves was determined

using the closed reflux, colorimetric method, APHA 5220D (APHA, 1995). The sample

was digested using K2Cr207, H2SO4, and HgSO4. Tests were conducted using Hach

prepared reagants, and analyzed on a Hach DR-3000 colorimetric instrument at the

laboratory of the University of Florida Water Reclamation Facility.

Total suspended solids

Total suspended solids (TSS) in the wastewater were determined using the

filterable residue, a gravimetric method with the material dried at 180C, EPA method

160.1 (EPA, 1993), method 2540DSM (APHA, 1995). 250 ml. samples were collected

from the seven points described above and stored for shipment to the Water Reclamation

Laboratory, University of Florida, where the tests were conducted.









Fecal coliform bacteria

Fecal coliform in the wastewater was determined using membrane filtration and

most probable number (MPN) of colonies per 100 ml of sample. This is method

9222DSM (APHA, 1995). Samples (175 ml) were collected from the seven points

described above and transported to the laboratory in Cancun for analysis within hours of

collection. The same laboratories that conducted the BOD-5 tests conducted the analyses

for fecal coliform until May 1998, when analysis was conducted in the water laboratory

of the Centro Ecologico Akumal.

Alkalinity

Alkalinity of the water samples was determined by titration (buret), method

2320B (APHA, 1995). Samples weighed 50 ml and the method used .02 N sulfuric acid.

Salinity

Salinity of water samples from the septic tank and wetlands was determined with

use of a hand-held refractometer accurate to +/- 0.5 parts salt per thousand.

Phosphorus Uptake by Limestone

Initial P content and uptake in wetlands

Samples of limestone were analyzed for initial phosphorus content and

phosphorus content after exposure to sewage in the treatment wetlands. Pre-exposure

limestone was collected during construction and bagged for later analysis. In December

1997 after one year of sewage treatment had occurred, composite limestone samples

were collected from each of the treatment cells of systems I and 2. These were divided

into limestone from the layer above the sewage line, and those at 0-10 cm depth, 10-20









cm depth, 20-30 cm depth, 30-40 cm depth and 40-50 cm depth. These limestone

samples were roughly pulverized mechanically then ground in a ball grinder.

Inorganic P analysis, conducted in the Wetland Biogeochemistry Laboratory at

the University of Florida, was determined as follows. Following grinding, the limestone

samples were dried in an oven at 70 deg.C. for 48 hours. Then a subsample (0.5 g) of the

ground limestone was extracted with 25 ml of 1M HCI for 3 hours, then filtered through

a 0.45 micrometer pore size membrane filter. The HCI extract was stored at 4C in a 20

ml polyethylene vial. The HCI extract was analyzed for inorganic P using an automated

ascorbic acid method (Method 365.1, EPA, 1995).

Calcium/magnesium composition of Yucatan limestone

The limestone was analyzed for calcium and magnesium content at the Soils

Laboratory of the Institute of Food and Agricultural Sciences (IFAS), University of

Florida.

The procedure was to grind and dry samples of limestone in a 120C oven for 4

hours. Then 5 x 1.0 gram dried sample was placed in a 1000 ml graduated beaker, and.

125 ml of IN HCI solution was added to dissolve the limestone. The solution was diluted

to 250 ml of 0.25M hydrochloric acid. The beaker was covered with a watch glass and

boiled gently on hot-plate for 10-15 minutes. Condensate was washed into beaker with

de-ionized filtered (D.I.) water and cooled to room temperature. The solution was

brought to approximate volume of 1000 ml. with D.I water. Analysis for

calcium/magnesium was by inductive coupled plasma spectroscopy.









Experiments on phosphorus uptake by limestone

To determine reaction kinetic rates of the Yucatan limestone with respect to

phosphorus, a series of lab and field experiments were designed. The experimental

procedure to determine phosphorus uptake by limestone was to combine limestone gravel

samples from the wetlands. Five hundred ml plastic bottles were filled with

approximately 250 grams of limestone gravel. Bottles were then filled with 450 ml of

phosphorus solution. This left some airspace below the neck of the bottles.

For the laboratory experiment, there were 5 experimental treatments x 3

replicates for a total of 15 bottles. The initial phosphorus concentrations were 5.6 mg

P/liter, 1 Img P/liter, 22 mg P/liter, 56 mg P/liter, and 111 mg P/liter. After addition of

phosphorus solution, bottles were maintained with caps only loosely on, allowing air

exchange. Bottles were shaken once a day. After 10 days, 10 ml. samples were taken and

filtered through a 0.45 pm membrane filter at 1,2,4,6 and 10 days. Separate syringes and

filter cases were used for each of the six treatments. Samples were stored in a freezer

until analysis for soluble reactive phosphorus.

For the field experiment, 3 x 500 ml. bottles with 250 grams of limestone gravel

prepared at the same time as the laboratory ones, were loaded with 450 ml of actual

wastewater from the septic tanks in Akumal, Mexico. Three bottles with 250 grams of

limestone were filled with 175 ml of actual wastewater (to approximate the condition in

the wetland treatment system that the sewage water covers the limestone). The bottles

had 10 ml. samples taken and filtered through a 0.45 micrometer membrane filter at

1,2,4,6, 10 and 30 days after loading. The samples were kept in a freezer until shipment

to the University of Florida Water Reclamation Laboratory for soluble reactive









phosphorus analysis. Analysis for soluble reactive phosphorus used EPA Method 365.1

(EPA, 1995)

Water Budget of the Wetland Systems

In May 1997 and December 1997 the water budget of the wetland systems were

determined by measuring inputs and outputs from the system. The only water inputs to

the systems are effluent from the septic tanks and direct rain, as no surface runoff or

groundwater enters the constructed wetlands. By draining the system 1 and system 2

septic tanks, and then measuring rate of re-fill, it was possible to estimate hydraulic

loading.

System evapotranspiration was calculated by measuring the decline over time in

the water levels of the standpipes in the control box at the end of each cell of the wetland

systems (see Figure 2-3 of the construction blueprints). Water-holding capacity of the

gravel used in the wetland was estimated by filling a known quantity (20 liter bucket)

with the limestone gravel and then measuring the amount of water that the volume holds.

The only outputs from the system are evapotranspiration and discharge from the

outlet in the control box of cell 2. Thus, once the average daily evapotranspiration is

calculated, the average discharge from the system may be estimated by difference from

average input from the septic tanks.

Economic Evaluation

Data on construction and maintenance costs of the wetland and package plant

sewage treatment systems were collected. Annual costs were estimated using expected

lifetimes of system components.









Emergy Evaluation

Comparative evaluations of the emergy involved in the wetland sewage treatment

system and a conventional "package plant" sewage system were carried out using survey

data on materials, labor, equipment used in constructing and operating the systems, plus

data on natural resource flow in the area. From these, emergy evaluation tables were

developed and emergy indices used to compare the sewage treatment systems.

Receiving Wetland


Biodiversity

Biodiversity of the mangrove area receiving discharge from Wetland system 2

was monitored for biodiversity before effluent began in December 1997. Biodiversity

was determined by ten transects of 100 individual plants identified to species. Shannon

diversity was then calculated from these data (see previous section).

Mangrove Soils

Depth of the mangrove soils in the vicinity of the wetland discharge was

determined in December 1997 by driving a piece of 1/8 inch steel rebar into the soil until

it struck rock. This was done in four directions, each 90 deg. from the next, from the

center of the discharge, with 20 total observations, each made at 3 m intervals. An

isopach map was generated from these data.

Wet/dry weight of the mangrove soils was determined in December 1997 by

drying five sample bags of 30 cm. deep soil cores at 70C until no further weight loss

was observed. Bulk density was calculated by taking five soil cores to a 30 cm depth and

then determining wet weight and dry weight after drying in an oven at 70 C until there









was no further weight loss. Five soil samples collected in December 1997 were analyzed

by the Soil Laboratory of the Institute for Food and Agricultural Sciences (IFAS),

University of Florida for total phosphorus and total nitrogen (using Kjeldahl method for

N and the dry ash method for P) and total organic content (by loss on ignition method).

These latter tests are described below:

Loss on ignition test for soil organic matter determination (Magdoffet al, 1996)

was used for soils with organic content greater than 6%. Five gram soil samples were

placed in a pre-heated oven at 120C for 6 hours. After cooling for 30 minutes, a weighed

subsample of soil was placed in a beaker and placed in a muffle furnace set to 450 C.

for at least 5 hours. For this study, samples were left for 14 hours. After cooling to room

temperature, final weight was recorded. Percent organic matter was determined by

comparing final weight with initial weight of the soil samples.

Total Kjeldahl Nitrogen (TKN) and dry ash method for phosphorus (Hanlon et al,

1998) were used by the IFAS Soil Laboratory in nutrient analysis of the mangrove soils.

In the TKN procedure, 0.5 g of soil is digested with 2.0 g of Kjeldahl mixture in a

digestion tube. The mixture is wet with pure water and 0.5 ml of concentrated sulfuric

acid is added. The tubes are placed on a preheated aluminum block digester at 150 deg C.

for 0.5 hours then the temperature is increased to 250C for 2 hours. One ml. of hydrogen

peroxide is added by pipette in two steps of 0.5 ml. A glass funnel is placed over the tube

and digestion continues for 2.5-3 hours. The tubes are removed from the digester and

cooled, then the sides of the tubes are washed with 5-10 ml of pure water. After mixing

with a vortex shaker, the digestate is moved to a 100 ml volumetric flask. Approximately

20 ml of solution is filtered through a Roger's Custom Lab 720 into a 90 ml. plastic cup.









A filtered subsample is transferred to a 20 ml. plastic scintillation vial and refrigerated

until analysis on the RFA (air-segmented, continuous-flow, automated

spectrophotometer). Final step is analysis on the RFA calibrated with digested standards

for total nitrogen.

In the dry ash P analysis, 1 g of oven-dry soil is combusted in a 500C muffle

furnace to ash for a minimum of 5 hours. The ash is then moistened with 5 drops of

distilled water and dissolved with 5 ml of 6.0M hydrochloric acid. After 30 minutes, the

solution containing the ash is transferred to a 50 ml volumetric flask and brought to

volume with pure water. A filtered subsample is transferred to a 20 ml. plastic

scintillation vial and refrigerated until analysis on the RFA (air-segmented, continuous-

flow, automated spectrophotometer). Final step is analysis on the RFA calibrated with

digested standards for total phosphorus.

Micro-analysis for soil composition

The mineral portion of the mangrove soils was assessed using X-ray diffraction

at the Soil Pedology Laboratory of the University of Florida.

After soil samples were mixed, organic materials were digested by addition of

sodium hypochlorite, 5.25% by weight, to cover the sample. After digestion for 20 hours,

each sample was put through a 15 micrometer sieve into distilled water. The soil sample

was centrifuged at 2500 RPM for 3 minutes and the supernatant liquid poured off. Then a

1 M solution of sodium chloride was added, and the solution again centrifuged at 2500

RPM and the supernatant poured off. Then de-ionized water was added to the solid

materials, and centrifuged at 3000 RPM for 5 minutes. Some of the liquid was poured

off, and oriented mounts were prepared for X-ray diffraction analysis by depositing









suspended materials onto porous ceramic tiles under suction. One of the tile mounts was

treated with potassium chloride, and two with magnesium chloride. The KCI and MgCI2

were added four times, and pulled through the ceramic tiles by a suction device. Then

each ceramic tile soil mount was rinsed with de-ionized water four times. To one of the

MgCl2 treated tiles, 30% glycerol was added. The clay tiles were then analyzed by X-ray

diffraction. Samples were scanned from 2 to 60 degrees 20 using a computer-controlled

x-ray diffraction system equipped with stepping motor and graphite crystal

monochromator. Power was 35 kV and scanning rate was 2 20 per minute.

Nutrients

Mangrove soil samples collected before and after discharge commenced, at the

beginning of May 1998 and monthly from June to August 1998, were analyzed using the

Total Kjeldahl Nitrogen and Dry Ash Phosphorus methods described above in the section

entitled Mangrove Soil. Soil samples were collected at 1, 3, 5 and 10 meters east, west,

north and south of the discharge point. Mangrove water samples collected in December

1997 and April 1998 were analyzed for biochemical oxygen demand, fecal coliform,

suspended solids, total nitrogen, total phosphorus, salinity and alkalinity using methods

described in the section on Analytic Measurements. These tests were repeated after

discharge commenced in May, and monthly samples were collected June, July, and

August 1998 to ascertain changes in the nutrient and water quality status of the mangrove

groundwater.









Hydrogeology

Water in the mangrove site at Akumal exchanged through groundwater channels

from below. There was no surface connection to the sea. Hydrologeological studies of the

fluxes with the receiving area were made by comparing surface water levels with those of

a nearby cenote (well) and the sea. This was done with a water level chart recorder of

surface water height during May 1997, December 1997 and July 1998

Direction of water flow in the area was determined from the heights of water in

three polyvinyl chloride (PVC) pipes, 10 cm in diameter, placed 60 cm deep in the

mangrove soils, which served as piezometers. Elevations were determined by use of

manual water-tube levels. Location and directional orientation of the piezometers was

determined with a surveying level. Water levels in the piezometers are equal to the

elevation of the hydraulic head (Fetter, 1994). Flow lines were determined by

triangulation of these data on a map of the potentiometric surface in the vicinity of the

discharge outfall. A series of 5 PVC monitoring pipes were installed in December 1997.

One pipe was installed 1 meter upstream from outfall of the discharge pipe from the

wetland, and three other pipes were installed 1,3 and 6 meters in the direction of water

flowlines in the mangrove. The fifth monitoring pipe was installed 12 meters southeast of

the discharge pipe, in the direction of the edge of the mangrove.

Simulation Model of the Water Budgets


Simulation models were developed for the treatment units and their discharge into

the receiving wetland. This model followed the methodology outlined in Odum (1994)

and Odum and Odum (1996). After selecting a system boundary, outside sources were









listed, from the environment and from the human economy. Relationships and pathways

between system components were identified including exports from the system.

Relationships were translated into energy language symbols and then into rate equations.

After average values were put on the pathways and in storage symbols, coefficients were

calculated with spreadsheet. A simulation program was written in BASIC and sensitivity

studied with scenarios. Simulation runs were compared with field and literature data.

Evaluating Potential of Wastewater System for the Coastal Zone


Potential significance of the treatment system was studied by considering a square

kilometer of developed coastal area operating the treatment system. Evaluations were

done on two scales: the treatment systems and the square kilometer.

Emergy Evaluation

An emergy evaluation of the square kilometer area was made using data from

published sources, data on use of natural resources and human services obtained from

hotel owners, homeowners and residents, and from town maps showing density and

layout of properties in the area.

Emergy analyses followed methods developed by Odum and Brown (Odum,

1996; Doherty and Brown, 1993; Brown and Ulgiati, in press). This was done by

developing systems diagrams showing energy sources, system components, pathways of

energy and material flow in the system, system outputs and depreciation/heat sinks.

These systems diagrams were developed in three forms: detailed, aggregated and three

arm diagrams. Then data was collected, using published and new data, on material and

energy flows.









Transformities

Emergy tables were compiled, using transformities for the items. Table 2-1

presents the transformity values used in all the emergy evaluations of the present study.

With these system relationships and data, indices to compare emergy flows of the

environment with those of the natural environment are evaluated. Among the indices

evaluated were the investment ratio, emergy yield ratio, ratio of nonrenewable to

renewable resources and empower density. These emergy indices characterize the

intensity and balance of environmental vs. developed resources (Odum, 1996).

Economic Evaluation

Economic impact on the square kilometer coastal area were compared for the use

of treatment wetlands or conventional package plant treatment systems. These data were

evaluated as a percentage of overall capital investment and yearly monetary flow.

Regional Water Budget

A regional water budget for a square kilometer of coastline in the study area was

developed including precipitation, inflow of groundwater from inland, tidal exchange,

evapotranspiration, pumped water and sewage. Budgets were compared for development

with no sewage treatment and development with treatment by constructed wetlands.

Regional Nutrient Budget

Regional nutrient budgets were developed for the same scenarios that of

development of a square kilometer of the Akumal coastal region. Nutrient budgets for

nitrogen and phosphorus were examined for the scenarios of fidull development without

sewage treatment and with treatment by constructed wetlands.









Table 2-1 Transformities and emergy per mass used in this study.


Item


Transformity
Sej/J
solar emjoule/joule


Sunlight
Wind, kinetic
Rain, geopotential
Rain, chemical potential
energy
Tide
Waves
Earth cycle
Wood
Groundwater
Gas
Motor fuel (liquid)
Primitive labor
Food
Hurricanes
Electricity (global average)

Agricultural and forest
products
Untreated wastewater
Concrete
Plastic products
Pulp wood
Sand
Limestone
Steel + iron products
Potassium chloride

a Odum, 1996
b Odum and Odum, 1983
c Brown etal, 1992
d Scatena et al., in press
e Christiansen, 1984
f Green, 1992
g Odum etal., 1983
h Brown and McClanahan,


Emergy per mass Reference
Sej/gram
solar emjoule/gram


1 (by definition) a
6.63 E2 a
8.888 E3 a
a
1.5444 E4
2.3564 E4 a
2.5889 E4 a
2.9 E4 a
3.49 E4 c
4.8 E4 a
4.8 E4 a
6.6 E4 a
8.1 E4 b
8.5 E4 c
9.579 E4 d

1.736 E5 a
2E5 c

5.54 E5 f
7.0 E7 h
9.26 E7 c
2.75 E8 e
1.0 E9 a
1.0 E9 a
1.78E9 a
1.1 E9 a
1.25 E10








1992














CHAPTER 3
RESULTS

Treatment Mesocosms


Design and Operation of the Wetland Units

In August 1996, the two wetland sewage treatment systems were constructed.

One, henceforth referred to as "wetland system 1" was designed to treat the wastewater

of 16 people and covers an area of 50.6 inm2. The second, "wetland system 2", designed to

handle the sewage of 24 people, has an area of 81.2 min2.

The treatment process for each wetland begins with a well-sealed two-chamber

septic tank which receives wastewater from the residences and offices by gravity flow.

Solids settle out in the septic tank which serves as primary treatment, and the

commencement of microbial treatment of the sewage. A filter at the discharge pipe from

the septic tank ensures that no solids larger than 1/64 inch can enter the wetland. Effluent

from the septic tank overflows by gravity feed into a header pipe which distributes the

sewage along the total width of the first of two treatment cells (compartments) of the

constructed wetland.

These wetlands were designed as subsurface flow systems, and have a cement

liner and sides to prevent movement of untreated sewage into the groundwater. They

were filled with limestone gravel to a depth of 0.6 m. Each cell of the wetland has a

collector, perforated 4 inch PVC pipe at the end which direct wastewater into the









centrally-located control box. Inside the control box, an adjustable standpipe determines the

level at which wastewater is maintained in the wetland, as wastewater overflows its

open end either from Cell 1 into the header pipe for Cell 2, or from Cell 2 to final discharge.

Normally, the standpipe is fully vertical at a height of 55 cm. The wastewater is kept 5 cm

below the level of the gravel. The sides of the system are at least 15 cm above the top of the

gravel to allow for natural litter buildup and to prevent overflow in heavy rains. The terrain

was graded to preclude surface water runoff inflow into the wetland systems. Hydraulic

residence with design loading is 5-6 days depending on seasonal evapotranspiration.

After the cement liner was completed, the system was filled with water and leak-

tested. Then the gravel was added and leveled. Larger limestone rock (5-10 cm) was used

in the first and last meter of each cell, around the header and collection pipes, to minimize

the dangers of clogging. After the addition of the gravel, the systems were filled with

tapwater and planted with wetland plants gathered from nearby wetlands, or purchased from

botanical gardens or commercial plant nurseries in the area. Soil was not introduced into the

system, except for rootballs of the plants. The plants were planted with at least 2-5 cm.

contact with the water. After planting, the two wetlands were mulched with 2-4 cm sawdust.

After discharge from Cell 2 of the wetland, the wastewater from System 1 enters

perforated drainage pipes that slope away from the wetland. The trenches in which these

pipes were laid were back-filled with limestone gravel to prevent clogging by dirt. System 2

effluent is sent to the nearby mangrove wetland and discharged near soil surface.

The blueprint drawings (Figures 3-1 to 3-10) show additional details of the

construction. Limestone gravel depths were increased for wetlands built subsequently to this

research in the area were done to a design specification of 80 cm to increase hydraulic








Subsurface Wetland
Sewage Treatment
Design, Mark Nelson
Pafle I oF 10 ,Date' 10/02/97


Overall


Isometric


View


Copyrloht 19971 Mark Nelson, ConFIdentlaLt


Notes
DAll wattlls 4'waterproof concrete, leak test
cells and control boxes before grovel fill
P)Backfill and grade all sides of wetQland to
prevent rainwater spillover
3)Trenches for leach field piping covered with
gravel and filltted to prevent dirt clogging


Figure 3-1 Construction blueprint: isometric view of the wetland treatment system.







Subsurface WetLand
Sewage Treatment
Deslgni Mark Nelson
Page 2 of 10 |Date, 10/02/97


2'-5 3/a8'


S.-<"


Overall.


Isometric


View of Piping


Copyright 19971 Mark Nelson, Confidential


Notes
D)Al Piping 4' PVC, see details pages 6 and 7
2)Septic tank and leach Field gravity Feed
require at least I to 50 slope For proper f
3)Septic Tank and/or grease trap require
Zoabel Filter
4)Cover all piping to prevent sun damage
5)Collector pipe risers optional
6)Renovable caDs on risers


Figure 3-2 Construction blueprint: isometric view of piping in the wetland system.


-


6k.P
-pr
.J i


"-A








Subsurface Wetland
Sewage Treatment
Design, Hark Nelson
Page 3 of 10 IDate, 10/02/97


Stones 2' to 4'
to surface

Pea Gravel
31' Deep
Mulch
/- l*Deep


i

I-..


ninlInun 6"


Center


Section


View


Copyright 1997, Harlk Nelson, Confidential


Notes#
D)AI walls 4' waterproof concrete
2)Vaterlevel 30. pea gravel 31' deep
3)Mutch layer 1' applied after planting
4)2' to 4' rock fillt to 31', cover with nulch
4 places
5)All rock and gravel fill must be washed
6)2' to 4' rock around collector pipes not
shown due to perspective
7)Positlon standpipe next to one wattll of the
control box ensuring that It can be lowered to
horizontal position within the control box


Figure 3-3 Construction blueprint: center section view of the wetland system.







SubsurFace Wettand I


Sewage Treatment I


Design, Mark Nelson l
Page 4 oF 10 Mlate, 10/02/97


Stones 2' to 4'
dia., to surface


Pea Gravel
31' Deep

Mulch
-- 1'Deep


I. (,'


Stones 2' to 4'
dla. to surface

Pea Gravel
31' Deep

Hutch
/- 1'Deep


Side Section


Showing Fill Materials


Copyright 1997a Mark Nelson, Confidentialt


Notes'
l)AIl watts 41 waterproof concrete
2)Vater level 30', pea gravel 31' deep
3)Mulch layer 1 applied after planting
4)2' to 4' rock Flit to 31', cover with nulch
4 places
5)Altl rock and gravel Fill nust be washed


I__________________________________


Figure 3-4 Construction blueprint: side section showing fill
system.


materials in the wetland


|


nilnlnun 6'







Subsurface Wetlandc
Sewage Treatment
Design Mark Nelson
Page 5 of 10 IDatei 10/02/97


Box Detail with


Dimensions


1997, Mark Nelson, Confidential


Notes'
1)1' thick wood control box cover, seated with
rubber gasket to prevent odor and Mosquito
breeding
2)4' waterproof concrete walls
3)Posltion standpipe next to one wall of the
control box ensuring that It can be lowered
horizontal position within the control box


Figure 3-5 Construction blueprint: control box with dimensions ofthe wetland treatment
cells.


Copyright








Subsurface Wetland
Sewage Treatment
Design. Mark Nelson
Page 6 of 10 jDate. 10/02/97


b. ^


Cell 1 Header Deteail


Copyright 19971


Mark Nelson, ConFidential


Notes
)Alt hatoles drlUed at centerline of 4* pipe
2)Durlng rock Filling, pipe must remain level
3)Septic tank and/or grease trap require
Zabel filter to prevent solids from entering
treatment system


Figure 3-6 Construction blueprint: treatment cell I header detail of the wetlands.


I









SubsurFace W/etland
Sewage Treatment
Desl ni Mark Nelson
Page 7 of 10 |Da'te 10/02/97


Cell 2 Header Detail



Copyright 19971 Mark Nelson, Confidential


Notes
1)4 PVC pipe sow scored at 1I Intervals
2)Ensure that during rock FlU, header pipe
renalns Level


Figure 3-7 Construction blueprint: treatment cell 2 header detail of the wetlands.


I








SubsurFace Wetland
Sewage Treatment
Design' Mork Nelson
Page 8 oF 10 IDate, 10/02/9


Large


Copyright 19971


System


Drainfield


Detail


Mark Nelson, Confidential


Notes,
D)Eoch drolnFleld pipe nust have a riser with
renovable cap for maintenance
2)Dralnfleld piping must have a nin. slope of 1150
for proper flow
3)Anount of dralnFleld needed depends on
system size


Figure 3-8 Construction blueprint: schematic showing drainfield detail for large wetland
systems.








SubsurFace \ettand
Sewage Treatment
Design' Mark Nelson
Poae 9 oF 10 IDate, 10/02/97


4-
1.
-~
A.


Small System


DrainField Detail


Copyright 1997i Mark Nelson, Confidentlal


Notes,
)DDralnfleld pipe nust have a riser with
removable cap for Maintenance
2)Dralnfield piping Must have a min. slope of 1'50
for proper flow
3)Amount of dralnfleld needed depends on
system size


Figure 3-9 Construction blueprint: schematic showing drainfield detail for small wetland
systems.







Subsurface Wetland
Sewage Treatment
Design' Mark Nelson
Poage o 10 DoF oDate, 10/02/97


Cover gravel with
6' sand or soil,


Geo-Textlle
Cloth







6' min. gravel
under pipe


4' perforated
drain pipe, silts
facing down


Drainfield


Cross


Section


Notes
lDMIn. slope 1,50 For proper Flow
2)Pipe perforated with saw cuts
3)Cross section shown here applies to all
dralnFleld Installations unless specified other-
wise


Copyright 19971 Marl Nelson, ConFidential I


Figure 3-10 Construction blueprint: drainfield cross-sectlion drawing or wetland system.









retention time, rather than the 60 cm of limestone used in the two research wetlands of this

study.

Ecological Characteristics

Patterns of biodiversity and dominance

In May 1997, December 1997 and July 1998 (nine, fifteen and twenty-three months

after planting, respectively) examinations of the wetland systems for species diversity was

conducted with the assistance of Edgar Cabrera, a botanist from Chetumal, Quintana Roo. A

total of 68 species were identified in May 1997, 70 species in December 1997 and 66 species

in July 1998 (Table 3-1). Species native to the Yucatan constituted 47 of the 66-68 species

present in May, 1997 and December 1997, with the remainder being cultivated and

introduced species.

Plant species richness (total number of species present) in each treatment cell

decreased slightly over the course of the study as shown in Figures 3-11, 3-12 and 3-13. For

example System 1 Cell 1 had 41 species in May 1997, 37 species in December 1997 and 35

species in July 1998; while System 1 Cell 2 had 37 species in May 1997,35 species in

December 1997 and 36 species in July 1998. In May 1997, wetland System I averaged 39

plant species per cell, in December 1997 and July 1998, the average was 36 species.

Wetland System 2 averaged 47 species per cell in May 1997,45 species in December 1997

and July 1998.

Considering the systems as a whole, in May 1997 there were 63 species in System 2

(with 482 observations), 17% higher than in wetland System 1 with 54 species (from 482

observations) (Figure 3-14). By December 1997, plant species had declined by about 10% in









Table 3-1. Plant species in the treatment wetlands from surveys of May, 1997, December,
1997 and July, 1998. Total number of species as of May, 1997: 68 species; as of December,
1997: 70 species, as of July, 1998: 66 species.


Scientific Name

D2 Acalypha hispida

Acrostichum danaefolium
Ageratum littorale

Alocasia macrorhiza


N2 Aloe vera
N2 Alternanthera
ramossissima
Dl Angelonia angustifolia

Anthurium
Schlechtendalii
N1 Anthurium sp.
Asclepias curassavica
Dl Bambusa sp.
Bidens pilosa

Bravaisia tubiflora
Caladium bicolor
Canna edulis

N2 Capraria biflora
Carica Papaya
Dl Cestrum diurnum

Chamaedorea Seifrizii
Chamaesyce
hypericifolia
Chrysobalanus icaco


Common Name

Cola de gato; cat's
tail
Helecho


Mafota; elephant
ears, taro

Sabila




Moco de povo



Bambu; bamboo
Margarita

Sulub
Bandera
Platonillo; canna
lilly
Claudiosa
Papaya
Galon de noche

Palma camedor


Icaco


NI1 Cissus sicyoides
Cissus trifoliata


Citrus Aurantium


Naranja agria;
orange tree


Notes: N = Native, I =
Introduced; C= Cultivated
C; red cattail flowers

N; wetland fern, to 3 m
N: blue-flowering little shrub
(purplish flowers); annual
I; starchy root, very shiny
Large leaves; leaf is straighter
and flatter than Xanthosema
C;
N

N; delicate shrub, purple
flowers
N; epiphyte

N
N; orange and yellow flowers
I;
N; yellow or white flowers
(like daisy)
N; pink flowers like bells
C; decorative taro
I; yellow flowers

N
N; edible fruit
I; shrub/tree CEA Cell 2, long
thin leaves
N; palm
N; delicate shrub with tiny
white flowers
N; woody, sturdy shrub with
thick leaves
N;
N; vine, elongated, ovate
leaves
C; edible fruit




















N2
Dl
D2
N1
NI;
D2


Scientific Name

Coccoloba uvwifera

Conocarpus erecta

Corchorus siliquosus

Cordia sebestena

Crinum amabile
Cucumis melo
Cyperus ligularis
Delonix regia
Desmodium incanum


N2 Desmodium tortuosum
Distichlis spicata.
Dl Eclipta alba

Eleocharis cellulose
DI Eleusmine indica
Eupatorium albicaule

DI Euphorbia cyathophora

Dl Eutachys petraea

Flaveria linearis
Hymenocallis littoralis
N1 Ipomoea indica


N1;
D2


Ipomoea Pes-caprae
Iresine celosioides


Ixora coccinea

Kalanchoe pinnata
Dl Lactuca intybacea
D2 Lantana involucrata


Common Name

Uva de mer; sea
grape
Botoncillo;
buttonwood tree


Siricote

Lidio reina
Melo; melon
Zacate cortadera
Poinsettia


Spike reed grass


Lirio/Spider lilly
morning glory

rinonina


Ixora


Milk weed
oregano xiru


N2 Leucaena glauca


Notes: N = Native, I =
Introduced; C=Cultivated
N; beach tree, prostrate or
upright
N; mangrove area tree

N; woody shrub, long-hard
seed pods (tree)
N; tree with large leaves, (next
to Eleocharis CEA Cell 2)
C
I; melon vine
N;
C;
N; 3-leaved leguminous vine

N
N; grass
N; like botoncillo with dots on
leaves;
N; short wetland reed
N;
N: 2 notches on leaves nearer
base
N;

N; grass with "feathers" on
ends
N; yellow flowers
N; white flowers;
N; vine with heart-shaped
leaves
N;vine, morning glory family
N; flowers are scales

I; yellow or orange flowers,
low shrub
I;
N; CEA Cell 1
N; small flowering shrub,
woody shrub; small serrations
on leaves; succulent; fragrant
leaves
C









Scientific Name

NI; Lochnera rosea
D2
Dl Ludwigia octavalis
Dl Lycopersicum esculenta
D2 Melanthera nivea


N2 Mimosa sp.
Malvaviscus arboreus
Musa sp.
Nerium oleander
N1 Nopalea cochinillifera
Paspalum virgatum
Pedilanthus
tithymaloides
N1; Pelliciera alliacea
D2
Philodendron sp
Phyla nodiflora



N2 Phyllanthus niruri
Pluchea odorata
Dl Porophyllum punctatum

DI Portulaca oleracea

Psychotria nervosa
Rabdadenia biflora

N2 Rhizophora mangle
Rhoeo discolor

Sansevieria triasiate
Scindapsus aureus
N1; Selenicereus Donkelaarii
D2
Senna biflora


Common Name

Teresita


Tomate; tomato




tulipancillo
Platano; banana
Oleonder; oleander
Napolito
Sacate


Santa Maria


Verdolaga; moss
rose



Red mangrove
Platonillo morado;

Lengue de suegra
Telefono


Modrecacao


Dl Sesbania emerus


Notes: N = Native, I =
Introduced; CCultivated
C; lavender flowers

N; yellow flowers
I; tomato plant
N; small button-white flowers
on sprawling shrub; 3-lobed
leaves
N
N; red flowers, tree
C; edible fruit
I; pink flowers, small tree
C; cactus; used as food
N; sharp-leaved clump grass
I;

N; long stalk, delicate flower

N;
N: red stems, white flowers,
sprawling shrub with sharp
notches near tip of leaves,
deep-grooved veins
N
N; purple flowering shrub
N; decorative black dots on
leaves, shrub, small leaf
N; various colors

N;
N; "mangrove-like" vine CEA
Cell 2
N
N; purple and green leaves,
roseatte form
C; small agave-like
C; variegated leaves
N: viney, thin cactus

N; tree with rounded leaves;
with a bunch of small, varied
colored flowers
N; tree with leguminous leaves









Scientific Name

Sesuvium portulacastrum

Dl Solanum erianthum
Solanum Schlechtendalii

N1; Syngonium sp.


NI:
D2
NI

N1;
D2


Terminalia Catappa

Thrinax radiata
Typha domingensis
Vigna elegans


Common Name

Verdolaga de playa;
succulenta


Almendro

Chit
Tule; cattail


Vigna luteola


Viguiera dentata


Washingtonii robusta

N1 Wedelhia trilobata
Xanthosoma roseum

Zamia purpuraceus
N 1 Zephyranthes Lindleyana


Washingtonii palm


mafata; taro,
elephant ears


Notes: N = Native, I =
Introduced; C=Cultivated
N; beach succulent

N;
N; red berries like small
tomatoes
N; palmate leaves, 5-folias

C; comer PCRF Cell 1 nr
septic tank; tree
N; palm, used for thatching
N; to 3-4 m
N; vine, 3-leaves, purple
flowers
N; yellow flower otherwise
similar to V. elegans (77)
N

C: palm tree; sharp thorns on
fronds
N; vine, yellow flowers
N; starchy root; soft-leaved and
more curved leaf form of taro
C; purple flowering shrub
C; thin, short blades, grass-like
with pink flower


Plant species identified by Edgar F. Cabrera, Chetumal, Q.R. on surveys in May and
December 1997, and July 1998.Code for column 2, DI = dead or not found in December
1997 survey but present in May, 1997 survey; N1 = new in December 1997 survey; D2 =
dead or not found in July, 1998 survey, N2 = new in July 1998 survey.

Botanic names: Cabrera, Martinez (1987), UNAM (1994), Brummitt (1992).



























*System 1, 1st treatment compartment
--- System 1, 2nd treatment compartment
-A- System 2,1st treatment compartment
-- System 2, 2nd treatment compartment


1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193 201 209 217 225 233
Number of observations in transect, May 1997

Figure 3-11 Species-area curves for each of the four wetland treatment cells, May 1997
data.


























--- System 1, 1st treatment compartment
--- System 1, 2nd treatment compartment
-A- System 2, 1st treatment compartment
-*- System 2, 2nd treatment compartment


1 10 19 28 37 46 55 64 73 82 91 100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244

Number of observations in transect, December 1997

Figure 3-12 Species-area curves for each of the four wetland treatment cells, December,
1997 data.























!E 35
0

A 30
0
0.
4)
._ 0


o 25
L-
0
E
20



E 15



10


5h




0 flt i m 19 9 i9t1 l 9 Il II9 I III H I II III t iff Iiff IIIII of I I II 111fi 11 III t 9 9t91 ill I III 11111i If III# I I 1i tff II I II 11111 it ll I tif1 99 I P11` l I I1 9 I + 11 94191 t1| 4 fl t 99t4i1919tt I99499| 11 1 1 *t 9 I 9II 1tt9 99|ti |itt 11 F 1t 9 I I M OW1|9 I99 *t1 i it9if t
,-. N ,) r ,- (0 ,. 0 0, 0 -_ N N "- IfU ,1 f 0 r',- in 0 M

Number of observations In transects July 1998N

Figure 3-13 Species-area curves for each of the four wetland treatment cells, July, 1998
data.


-U-Wetland system 2 Cell 1
- Wetland system 1 Cell 1

-M- Wetland system 1 Cell 2
-4-Wetland system 2 Cell 2












60 ..................... ...... ................... ....... ........... ... ............. ......




o 5 0 .....................................
4)


0.
40 ............
CL
30

ME 30
C


E 20 ... ... .. ..... ........... .......... .... ..... ..












Number of observations in transect, May 1997

Figure 3-14 Species-area curves for the 50.6 m2 wetland unit (system 1) and the
81.2 m2 wetland (system 2), May, 1997. Transects counted 482 individuals in each
system.


--- Wetland treatment system 1
--Wetland treatment system 2









the individual wetlands (Figure 3-15) although overall number of species present in both

wetlands increased slightly (from 68 to 70 species). Many of the species no longer present

were low, understory shrubs, while almost half the newly present species were native vines.

In July 1998, System 1 lost an additional 10% of species, with a total of 44 species,

while System 2 remained constant at 57 (Figure 3-16), although again both numbers included

a loss of some previously present species and establishment of new species (Table 3-1).

Comparison with natural ecosystems

In December 1997, transects with 1000 observations showed 73 species present in the

inland tropical forest ecosystem, and 17 species in the natural mangrove wetlands, compared

with the 70 species found in the constructed wetland treatment systems (Figure 3-17). Table

3-2 lists the species found in the mangrove and Table 3-3 presents the species found in the

forest ecosystem. Figure 3-18 compares number of species in treatment wetland systems 1

and 2 with number of species found in the transects through forest and mangrove ecosystems.

The wetlands had diversity of plant species comparable to that found in nearby forest

ecosystems and a much greater number of species than were found in the adjacent mangrove

wetlands.

Dominance

Dominance was assessed through species relative frequency, Shannon diversity

index, percent cover, estimate of areal coverage and importance value.




































Figure 3-15 Species-area curves for the 50.6 m2 Yucatan wetland (system 1) and the
81.2 m2 wetland (system 2), December, 1997. Transects counted 500 individuals in each
system.


-*- Wetland treatment system 1
--0-Wetland treatment system 2











60






50



1a

4-
lo
C 40
a)
'0
(0
V
._





0





E
30
.0






10


Figure 3-16 Species-area curves for the 50.6 m2 Yucatan wetland (system 1) and the
81.2 m2 wetland (system 2), July, 1998. Transects counted 500 individuals in each
system.


---Wetland system 1
-f-Wetland system 2










-4


0~ ______ __________________ _________________------------ ----- ---------




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