Citation
Radium-226 Accumulation in Sediments of Groundwater-Augmented Lakes in Hillsborough County, Florida, USA

Material Information

Title:
Radium-226 Accumulation in Sediments of Groundwater-Augmented Lakes in Hillsborough County, Florida, USA
Creator:
Dearmond, Brandy S
Place of Publication:
[Gainesville, Fla.]
Florida
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (60 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Geology
Geological Sciences
Committee Chair:
Brenner, Mark
Committee Members:
Jaeger, John M.
Hodell, David A.
Graduation Date:
12/14/2007

Subjects

Subjects / Keywords:
Aquifers ( jstor )
Bodies of water ( jstor )
Calcium ( jstor )
Crystals ( jstor )
Groundwater ( jstor )
Lakes ( jstor )
Phosphorus ( jstor )
Radionuclides ( jstor )
Sediment core samples ( jstor )
Sediments ( jstor )
226, augmentation, cores, florida, geochemical, lakes, radioisotope, radium, sediments
Geological Sciences -- Dissertations, Academic -- UF
Hillsborough County ( local )
Genre:
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Geology thesis, M.S.

Notes

Abstract:
I analyzed 226Ra activities in surface sediment samples from Lake Charles, and in sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal, Hillsborough County, Florida (USA). The four lakes have received groundwater input from the deep Floridan Aquifer since as early as the 1960s in order to maintain lake levels. Surface sediments from Lake Charles were analyzed for organic matter and radionuclide (Radium-226, Lead-210, Cesium-137) activities. Cores from the four study lakes were analyzed for stratigraphic changes of organic matter, phosphorus, radionuclides (226Ra, 210Pb, 137Cs), and cations (Calcium, Magnesium, and Strontium). Organic matter concentration in 30 surface sediment samples from Lake Charles ranged from 0.0% (i.e. pure quartz sand) to 38.4%. Organic matter content was positively correlated with water depth (r = 0.44, n = 30, P < 0.05). Radium-226 activities in surface sediments ranged from 0.6 dpm g-1 to 23.9 dpm g-1. Activities in surface deposits increased with greater water depth (r = 0.72, n = 30, P < 0.01). Radium-226 activity was positively correlated with organic matter content (r = 0.77, n = 30, P < 0.001). Surface sediment samples from Lake Charles represent material deposited recently, probably since the initiation of hydrologic augmentation. Radium-226 in these topmost deposits is associated primarily with organic matter. Sediments in most Florida lakes are composed principally of quartz sands and organic matter, but possess little inorganic silt and clay. A study of surface sediments from 34 Florida lakes demonstrated that both calcium and magnesium were positively correlated with OM content (Brenner & Binford 1986). Radium-226, another divalent cation, evidently behaves in a similar fashion, adsorbing to the OM fraction in the Lake Charles surface sediments. Higher 226Ra activities in sediments from deeper-water sites in Lake Charles may reflect the high concentration of fine organic particles at these deep locations. Top samples (0?4 cm) from sediment cores taken in Lakes Charles, Saddleback, Little Hobbs, and Crystal had 226Ra activities of 44.9, 17.5, 7.6, and 8.5 dpm g-1, respectively, about an order of magnitude greater than values in deeper, older deposits. The surface sample from Lake Charles yielded the highest 226Ra activity yet reported from a Florida lake core. Several lines of evidence suggest that groundwater augmentation is responsible for the high 226Ra activities in recent sediments: (1) 226Ra activity in cores increased recently, (2) the Charles, Crystal, and Saddleback cores display 226Ra /210Pb disequilibrium at several shallow depths, suggesting 226Ra entered the lakes in dissolved form, (3) cores show recent increases in Ca, which, like 226Ra, is abundant in augmentation groundwater, and (4) greater Sr concentrations are associated with higher 226Ra activities in recent Charles and Saddleback sediments. Sr concentrations in Eocene limestones of the deep Floridan Aquifer are high relative to Sr concentrations in surficial quartz sands around the lakes. Sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal display geochemical changes in their uppermost deposits. Cores from all four lakes show upcore increases in 226Ra activity, Ca, and Mg content. The Charles and Saddleback cores display a general increase in Sr concentration. The recent geochemical and biological changes in the sediment records are consistent with shifts that might be expected as a consequence of deliberate groundwater augmentation. Inadvertent addition of deep groundwater associated with past agriculture and residential development in the watershed also might have contributed to changes that are evident in the sediment record. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2007.
Local:
Adviser: Brenner, Mark.
Statement of Responsibility:
by Brandy S Dearmond.

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Source Institution:
UFRGP
Rights Management:
Copyright Dearmond, Brandy S. 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.
Classification:
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CHAPTER 1
INTRODUCTION

Florida is one of the fastest-growing states in the United States, with the Tampa Bay Area

a top contender for population growth. From the year 2000 to 2006, the United States Census

Bureau reported an estimated increase in population of 13.2% in the State of Florida, and from

2000 to 2005, Hillsborough County experienced a 12% population increase (U.S. Census Bureau

2006). The new construction of infrastructure, residential developments, schools, and

commercial businesses that accompanies rapid population growth places a strain on aquifers

(Stewart and Hughes 1974).

The deep Floridan Aquifer, which consists of Eocene to Miocene limestones (Scott 1997),

is the major source for human use in west-central Florida, and groundwater from it is withdrawn

at well-fields in Hillsborough County, Florida, USA (Figure 1-1). During the year 2000, total

fresh groundwater withdrawals from Hillsborough County ranged from 100 to 200 million

gallons per day (mgd), with 194.86 mgd of that removed from the Floridan Aquifer (USGS

2004). Only five years prior, during 1995, the total groundwater withdrawals were 169.22 mgd,

which included withdrawals from the Intermediate and Surficial Aquifers (Marella 1995). Since

1965, public supply groundwater use has increased from 18.80 mgd to 61.79 mgd in 1990 and

85.51 mgd in 2000 (Marella 1995 & 2004; SWFWMD 2002 & 2004). The population served by

the public water supply in Hillsborough County grew from 370,000 in 1970 to 816,641 in 1990

and 854,750 in 2000 (Marella 2004; SWFWMD 2002). The removal of deep groundwater has

increased downward seepage of both shallow groundwater and surface water, causing local lake

level declines. Along with anthropogenic effects, natural occurrences play a part in the decline

of lake levels. Lake stage decreases were exacerbated by droughts as well (Stewart and Hughes

1974), and Hillsborough County experienced a major drought in 2000. Some lakeside











Appendix A-2. Continued


Calcium
Concentration
(mg/g)


Magnesium
Concentration
(mg/g)


Sr Concentration
(mg/g)


Total Phosphorus
(mg/g)


Lake

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs

Little Hobbs


Sample
Depth
(cm)

4

8

12

16

20

24

28

32

36

40

44

48

52

56

60

64

68

72

76

80

84

88

92

96


%OM

38.1

38.7

38.8

38.8

38.3

36.9

34.4

43.5

52.9

56.4

58.5

59.3

58.9

57.7

48.0

37.3

26.8

20.4

5.0

4.0

3.2

3.3

2.8

3.0









Previous paleolimnological study of groundwater-augmented Round Lake (A = 5 ha, Zmean

= 2.4 m) near Tampa, Florida indicated augmentation, which began in 1966, increased 226Ra

input to the water body (Brenner et al. 2000). The lake receives about half its annual hydrologic

budget from pumped groundwater. Surface sediments (0-4 cm) from two Round Lake cores had

226Ra activities of 26.91.0 and 26.80.3 dpm g-1 dry (Brenner et al. 2000), the highest 226Ra

activities that had been measured in Florida lake sediments (Brenner et al. 1994, 1997). These

high activities were attributed to inputs of groundwater that is rich in dissolved 226Ra, which

adsorbs to near-surface sediments (Brenner et al. 2004). Previous experiments at Saddleback

Lake demonstrated that pumped groundwater was the principal source of Ra-226 to the lake

(Smoak and Krest 2006).

Radium-226 activity in topmost Round Lake sediment samples exceeded total 210Pb

activity, indicating disequilibrium between 226Ra and supported 210Pb. This phenomenon had

been reported for only one other Florida waterbody, Lake Rowell (Brenner et al. 1994). Isotopic

disequilibrium in Round Lake was linked to augmentation groundwater that passed through 238U-

rich carbonate-fluorapatite deposits in the underlying bedrock (Kaufmann and Bliss 1977;

Upchurch and Randazzo 1997). The upper Floridan Aquifer can have 226Ra activities that

exceed the drinking water standard of 11 dpm g-1 (Kaufmann and Bliss 1977). Coastal surface

waters off west central Florida that receive groundwater inputs display high 226Ra activities

(Fanning et al. 1982; Miller et al. 1990). High activities of 210Po, a decay product of 226Ra, have

been measured in Florida groundwater (Harada et al. 1989) and some of the highest values have

been measured in Hillsborough County (Upchurch and Randazzo 1997).

Potential Ecological and Human Health Risk Factors

Previous studies showed groundwater in Hillsborough County can contain high levels of

dissolved 226Ra. Groundwater augmentation of local lakes was also shown to have ecological









Dating Sediment Cores

Attempts to date the cores using gamma counting proved problematic. None of the cores

showed a distinct 137Cs peak (Figure 4-2). The 1963 bomb fallout peak is commonly blurred in

Florida lake sediments that lack 2:1 layer clays and bind cesium poorly (Brenner et al. 2004).

Soluble 137Cs is prone to transport within sediments and probably moves downward through the

sediment lens in these hydrologically "leaky" lakes. High and variable 226Ra activities in the

cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal create difficulties for 210Pb

dating. Disequilibrium between 226Ra and supported 210Pb makes it impossible to estimate

unsupported 210Pb activity accurately and confounds dating (Brenner et al. 2004). The large

amount of dissolved 226Ra introduced into the lakes will equilibrate with (supported) 210Pb only

after -110 years, i.e., about 5 half-lives (22.3 yr) of 210Pb. Deeper sediments in the cores, where

226Ra and 210Pb activities are low and similar, are probably >100 years old, as they apparently

possess no unsupported 210Pb. Another line of evidence that these are recent deposits is that

there is no 137Cs at great depth in the cores. In all four cores, it appears that more than a century

of accumulated sediment was retrieved (Figure 4-2).

Table 4-1. Correlation coefficients (r) of stratigraphic correlation between 226Ra activity and
concentrations of calcium (Ca), magnesium (Mg), total phosphorus (P), strontium
(Sr), and organic matter (OM) in sediment cores from Lake Charles, Saddleback,
Little Hobbs, and Crystal.
Lake Name Ca Mg P Sr OM (%LOI)
Charles (226Ra) 0.82*** 0.03ns 0.03ns 0.68*** 0.61***
Saddleback
(226Ra) 0.99*** 0.95*** 0.69* 0.98*** -0.96***
Little Hobbs
(226Ra) 0.94*** 0.68*** 0.89*** NM 0.56**
Crystal (226Ra) 0.94*** 0.44ns 0.03ns NM -0.08ns
Note: *p<0.05, **p<0.01, ***p<0.001, ns = not significant (p>0.05), n values for Charles = 29
(Ca, Mg) and 26 (P, OM), Crystal = 12, Little Hobbs = 22, Saddleback = 10, NM = Not
Measurable









sediment records are consistent with shifts that might be expected as a consequence of deliberate

groundwater augmentation. Inadvertent addition of deep groundwater associated with past

agriculture and residential development in the watershed also might have contributed to changes

that are evident in the sediment record.









I evaluated surface sediments from Lake Charles, and sediment core profiles in Lakes

Charles, Saddleback, Crystal, and Little Hobbs (Lake Lutz). The surface sediments were

analyzed for organic matter and radionuclide content. The cores from the four lakes were

analyzed for stratigraphic changes of organic matter, phosphorus, radionuclides (210Pb, 226Ra,

137Cs), and cations (Ca, Mg, Sr).

Study Lakes

All of the lakes in this study are located in northwestern Hillsborough County, in a region

of neutral to slightly alkaline, oligotrophic (lacking in plant nutrients, with a high oxygen

content) to mesotrophic (lakes with an intermediate level of productivity), clear-water lakes, and

on a moderately thick plain of silty sand that overlies Tampa Limestone (Figures 1-1 through 1-

5). Recent analyses by the Florida Department of Health showed 226Ra enters all four basins

with groundwater input. Triplicate samples run on augmentation water at Lake Charles,

Saddleback, Little Hobbs, and Crystal yielded mean 226Ra concentrations of 3.11, 3.26, 0.82, and

1.41 dpm 1-1, respectively. Location (latitude/longitude), surface area, maximum depth,

augmentation history, and hydrologic setting for the study lakes are summarized below:

* Lake Charles: 28006'57"N, 82028'52"W, small (6 ha), shallow (Zmax = 5.5 m), augmented
since summer 1968, part of the Rocky/Bushy Creek watershed

* Lake Saddleback: 2807'13", 8229'41", small (12.55 ha), shallow (zmax= 6.71 m),
augmented since summer 1968, part of the Rocky/Bushy Creek watershed

* Crystal Lake: 28007'59", 82028'40", small (6.5 ha), shallow (zmax = 7.9 m), augmented
since 1973, part of the Rocky/Bushy Creek watershed

* Little Hobbs Lake (Lutz Lake): 28009' 11", 82028'49", small (2.8 ha), shallow (zmax =
5.5m), augmented since the early 1970s, part of the Cypress Creek watershed










Randazzo 1997). The upper Floridan Aquifer can have 226Ra activities that exceed the drinking

water standard of 11 dpm g-1 (Kaufmann and Bliss 1977). Coastal surface waters off west

central Florida, south of the Tampa area, that receive groundwater inputs from the surficial and

Upper Floridan aquifers, and pass through Hawthorn group sediments, display high 226Ra

activities (Fanning et al. 1982; Miller et al. 1990). High 210Po activities have been measured in

Florida groundwater (Harada et al. 1989) and some of the highest values have been measured in

Hillsborough County (Upchurch and Randazzo 1997).


238
U
4.468E+9 yr
238.05078


214
Pb
26.8 min
213.99979
206
Hg
8.15 min
205.97749


Figure 2-1.


Radioactive decay of: U-238


234 234
--> Th --> Pa -->
4,270 MeV 24.10 da 6.420 MeV 6.70 hr 2,197 MeV
234.04359 234.04330
226 s 222
--> --> Rn -->
4,770 MeV 1,.,.. 4.871 MeV 3.8235 d 5,590 MeV
j1-- .:.- ':' 222.01757

214 210
i--> --> TI -->
1,024 MeV 19,9 min 3.272 MeV 1,30 min 5,484 MeV
213.99869 209.99006
206 B 206
--> --> Pb
1.308 MeV 4.199 min 1.533 MeV 24.1%
205.97609 205.97444
Stable

The decay of Uranium-238 to stable Lead-206.


234
U
2.455E+5 yr
234.04094
218
Po
3.10 min
218.00896


-->
4,859 MeV


-->
6,115 MeV



5,484 MeV
5,484 MeV









homeowners found their lakefront property was steadily increasing as the lake shore retreated.

Since the 1960s, some lakefront homeowners have been installing single deep groundwater wells

on the shoreline of their lakes to allow them to add groundwater to the lakes, i.e., augmentation.

The Southwest Florida Water Management District (SWFWMD), which was formed during the

1970s, is currently in charge of Hillsborough County's water resources, and has maintained

water levels in some of these augmented lakes with these wells.

Previous Limnological Studies

Augmentation and Lake Chemistry

During the 1970s, a few studies evaluated the effects of augmentation on lake hydrologic

budgets and water chemistry (Stewart and Hughes 1974; Martin et al. 1976a; Dooris and Martin

1979). Groundwater inputs altered the chemistry of lake waters (Martin et al. 1976a; Dooris and

Martin 1979). Prior to augmentation, most area lakes were "soft" and dominated by sodium

(Na ), sulfate (SO42-), and chloride (C1-), receiving most of their hydrologic input from rainfall

and surface runoff. Augmentation with deep groundwater converted water bodies into calcium

(Ca2+) bicarbonate (HCO3-1) systems. Augmented lakes have water column ion concentrations

with relative proportions similar to groundwater, and display high hardness, bicarbonate

concentration, and pH (Martin et al. 1976a).

Augmentation and Lake Biology

Other investigations explored the biological consequences of augmentation (Dooris et al.

1982; Martin et al. 1976b). Phytoplankton diversity is greater in augmented lakes and positively

correlated with water-column inorganic carbon (IC) concentration (Dooris et al. 1982). Martin et

al. (1976b) suggested groundwater augmentation might promote growth of exotic Hydrilla

verticillata. The Round Lake study also showed that the radionuclide apparently substitutes for

calcium in plant tissues and the shells, bones, and flesh of animals. Accumulation of 226Ra in









LIST OF REFERENCES


Andersen JM (1976) An ignition method for determination of total phosphorus in lake sediments.
Water Res 10: 329-331.

Brenner M, Binford MW (1986) Material transfer from water to sediment in Florida lakes.
Hydrobiologia 143: 55-61.

Brenner M, Peplow AJ, Schelske CL (1994) Disequilibrium between Ra-226 and supported Pb-
210 in a sediment core from a shallow Florida lake. Limnol Oceanogr 39: 1222-1227.

Brenner M, Schelske CL, Kenney WF (2004) Inputs of dissolved and particulate Ra-226 to lakes
and implications for Pb-210 dating recent sediments. J Paleolimnol 32: 53-66.

Brenner M, Schelske CL, Whitmore TJ (1997) Radium-226 stratigraphy in Florida lake
sediments as an indicator of human disturbance. Verh Internat Verein Limnol 26: 809-813.

Brenner M, Smoak JS, Allen MS, Schelske CL, Leeper DA (2000) Biological accumulation of
Ra in a groundwater-augmented Florida lake. Limnol Oceanogr 45: 710-715.

Brenner M, Smoak JM, Leeper DA, Streubert M, Baker SM (2007) Radium-226 accumulation in
Florida freshwater mussels. Limnol Oceanogr 52: 1614-1623.

Brenner M, Whitmore TJ (1999) Paleolimnological reconstruction of water quality for Lakes
Dosson, Halfmoon, and Round in Hillsborough County, Florida. Final Report to the
Southwest Florida Water Management District, Brooksville, FL.

Deevey ES (1988) Estimation of downward leakage from Florida lakes. Limnol Oceanogr
33:1308-1320.

Dooris PM, Dooris GM, Martin DF (1982) Phytoplankton responses to ground water addition in
central Florida lakes. Water Res Bull 18:33 5-3 37.

Dooris PM, Martin DF (1979) Ground-water induced changes in lake chemistry. Ground Water
17:324-327.

Fanning KA, Breland JA II, Byrne RH (1982) Radium-226 and radon-222 in the coastal waters
of west Florida: high concentrations and atmospheric degassing. Science 215:667-670.

Fisher MM, Brenner M, Reddy KR (1992) A simple, inexpensive piston corer for collecting
undisturbed sediment/water interface profiles. J Paleolimnol 7: 157-161.

Hfkanson L, Jansson M (1983) Principles of lake sedimentology. Springer-Verlag, New York,
316 p.









LIST OF ABBREVIATIONS

IN HCl: 1 Normal Hydrochloric Acid

137Cs: Cesium-137

210Pb: Lead-210

210Po: Polonium-210

214Bi: Bismuth-214

214Pb: Lead-214

222Rn: Radon-222

226Ra: Radium-226

238U: Uranium-238

A: Area

Ba: Barium

"C: Degrees Celsius

Ca: Calcium

Cl-: Chloride

cm: centimeters

dpm g-1: decays per minute per gram

H2SO4: Sulfuric Acid

ha: hectares

HCO3-1: Bicarbonate

IC: Inorganic Carbon

K2S20s: Potassium Persulfate

keV: kiloelectron volt

LOI: Loss On Ignition

m: meters











Appendix A-2. Continued






Sample Corrected Mean Corrected
Depth Ra-226 Activity a Ra-226 Pb-210 Pb-210 Cs-137 Cs-137
Lake (cm) (dpm g') Activity (dpm g') Error (dpm g') Error

Crystal 4 8.5 0.6 16.1 0.3 3.2 0.1

Crystal 8 6.8 0.4 16.6 0.4 3.7 0.1

Crystal 12 6.7 0.7 14.6 0.4 4.0 0.1

Crystal 16 4.6 0.3 10.3 0.3 2.1 0.1

Crystal 20 2.9 0.1 1.9 0.1 0.8 0.0

Crystal 24 2.0 0.3 2.3 0.2 0.7 0.0

Crystal 28 1.9 0.3 1.2 0.1 0.4 0.0

Crystal 32 1.7 0.1 -0.5 0.0 0.3 0.0

Crystal 36 1.7 0.3 1.7 0.1 0.2 0.0

Crystal 40 1.2 0.1 0.5 0.1 0.1 0.0

Crystal 44 1.3 0.2 1.6 0.1 0.0 0.0

Crystal 48 1.8 0.1 1.5 0.1 0.0 0.0









sediments and food webs of groundwater-augmented Florida lakes may prove to be common.

Likewise, groundwater pumping for other purposes such as agricultural irrigation, residential,

and industrial uses, may also contribute 226Ra to Florida's aquatic ecosystems (Brenner et al.

2004).

Diatom analysis from a core in Round Lake suggested groundwater augmentation

contributed to higher dissolved ion concentrations, slightly increased pH, and higher trophic state

conditions (Brenner and Whitmore 1999).

Diatom studies on the four lakes in this study indicate recent alkalization occurred in all

four (Brenner et al. 2006). Lake waters apparently change from pH values in the range of 5-5.8

to pH values in the range of 7.2-8. Ionic content also increased in all four study lakes, as

indicated by diatom salinity autecological (species ecological) data. Both of these changes are

consistent with what might be expected from the addition of groundwaters that are high in base

cation content. Trophic state appears to have increased in all four lakes, as demonstrated by

weighted-averaging calibration (WACALIB) derived estimates for total limnetic total P based on

diatom counts in cores (Brenner et al. 2006). Declines in dystrophic diatoms are probably, in

part, a result of augmentation with clear groundwater (Brenner et al. 2006).

Augmentation and Radioisotopic Studies

Several factors determine dissolved 226Ra concentrations in Florida lake waters and the

amount of 226Ra adsorbed to recent sediments: (1) 226Ra activity in pumped groundwater, which

is influenced by local geology, (2) rate of groundwater pumping, (3) proportional contribution of

groundwater to the lake's annual hydrologic budget, (4) lake water residence time, and (5)

mixing of augmented water throughout the lake. Sediment composition, particle size, deposition

rate, and the through-flow of 226Ra-rich water may also influence the stratigraphic distribution of

226Ra activity in sediments.







































figure 1-2. An aerial image ot Hlllsoorougn county, mondia.












Appendix A-2. Continued





Sample Calcium Magnesium Strontium
Depth Concentration Concentration Concentration Total Phosphorus
Lake (cm) %OM (mg/g) (mg/g) (mg/g) (mg/g)


Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles


4

8

12

16

20

24

28

32

36

40

44

48

52

56

60

64

68

72

76

80

84

88

92

Q


42.7

42.3

43.3

40.8

42.3

33.2

36.9

36.0

33.8

32.9

32.5

31.9

30.6

25.8

32.9

35.3

35.0

36.1

38.0

37.0

36.9

32.8

30.9

29.0

0.0

24.2

0.0

11.7

0.0







































figure 1-5. An aerial image ot Little Hobbs (Lutz) Lake, just west ot U.S. 41.











Lake Saddleback
Core Activity (dpmlg)


0 5 10 15


0


5


10


15


20


25


30


35


40


45


--Ra-226
--Pb-210
Cs-137


Figure 4-3. Continued









most Florida lakes are composed principally of quartz sands and organic matter, but possess little

inorganic silt and clay. A study of surface sediments from 34 Florida lakes demonstrated that

both calcium and magnesium were positively correlated with OM content. Radium-226, another

divalent cation, evidently behaves in a similar fashion, adsorbing to the OM fraction in the Lake

Charles surface sediments. Higher 226Ra activities in sediments from deeper-water sites in Lake

Charles may reflect the high concentration of fine organic particles at these deep locations.

Top samples (0-4 cm) from sediment cores taken in Lakes Charles, Saddleback, Little

Hobbs, and Crystal had 226Ra activities of 44.9, 17.5, 7.6, and 8.5 dpm g-l, respectively, about an

order of magnitude greater than values in deeper, older deposits. The surface sample from Lake

Charles yielded the highest 226Ra activity yet reported from a Florida lake core. Several lines of

evidence suggest that groundwater augmentation is responsible for the high 226Ra activities in

recent sediments: (1) 226Ra activity in cores increased recently, (2) the Charles, Crystal, and

Saddleback cores display 226Ra /210Pb disequilibrium at several shallow depths, suggesting 226Ra

entered the lakes in dissolved form, (3) cores show recent increases in Ca, which, like 226Ra, is

abundant in augmentation groundwater, and (4) greater Sr concentrations are associated with

higher 226Ra activities in recent Charles and Saddleback sediments. Sr concentrations in Eocene

limestones of the deep Floridan Aquifer are high relative to Sr concentrations in surficial quartz

sands around the lakes.

Sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal display

geochemical changes in their uppermost deposits. Cores from all four lakes show upcore

increases in 226Ra activity, Ca, and Mg content. The Charles and Saddleback cores display a

general increase in Sr concentration. The recent geochemical and biological changes in the

sediment records are consistent with shifts that might be expected as a consequence of deliberate









Harada K, Burnett WC, Larock PA, Cowart JB (1989) Polonium in Florida groundwater and its
possible relationship to the sulfur cycle and bacteria. Geochim Cosmochim Acta 53:143-
150.

Hazardous Substance and Waste Management Research, Inc. (2000) Human health risk
assessment and preliminary ecological evaluation regarding potential exposure to Radium-
226 in several central Florida lakes ecosystems. Report to the Southwest Florida Water
Management District, Brooksville, FL, 21 pp. + appendices

Hazardous Substance and Waste Management Research, Inc. (2004) Human health risk
assessment regarding potential exposure to Radium-226 in two central Florida lake
systems. Report to the Southwest Florida Water Management District, Brooksville, FL, 15
pp. + appendices

Kaufmann RF, Bliss JD (1977) Effects of phosphate mineralization and the phosphate industry
on radium-226 in ground water of central Florida. US Environmental Protection Agency
Final Report EPA/520-6-77-010. EPA Office of Radiation Programs, Las Vegas, NV

Krishnaswami S, Lal D (1978) Radionuclide limnochronology. In: Lerman A (ed) Lakes:
chemistry, geology, physics. Springer-Verlag, New York, pp 153-177

Martin DF, Victor DM, Dooris PM (1976a) Effects of artificially introduced ground water on the
chemical and biochemical characteristics of six Hillsborough County (Florida) lakes.
Water Res 10:65-69

Martin DF, Victor DM, Dooris PM (1976b) Implications of lake augmentation on growth of
Hydrilla. J Environ Sci Health 3:245-253

Metz PA, Sacks LA (2002) Comparison of the hydrogeology and water quality of a ground-
water augmented lake with two non-augmented lakes in northwest Hillsborough County,
Florida. US Geological Survey Water Resources Investigation Report 02-4032.
Tallahassee, FL, 74 pp

Miller RL, Kraemer TF, McPherson BF (1990) Radium and radon in Charlotte Harbor Estuary,
Florida. Estuarine, Coastal Shelf Sci 31:439-457

Moore WS (1984) Radium isotope measurements using germanium detectors. Nucl. Inst.
Methods 223: 407-411.

Schelske CL, Conley DJ, Stoermer EF, Newberry TL, Campbell CD (1986) Biogenic silica and
phosphorus accumulation in sediments as indices of eutrophication in the Laurentian Great
Lakes. Hydrobiologia 143: 79-86.

Schelske CL, Peplow AJ, Brenner M, Spencer CN (1994) Low-background gamma counting:
applications for 210Pb dating of sediments. J Paleolimnol 10: 115-128.









CHAPTER 4
RESULTS

Lake Charles Surface Sediments

Radioisotopic Results

Radium-226 activities in surface sediments in Lake Charles range from 0.6 dpm g-1 to 23.9

dpm g-1. Activities in surface deposits increase with greater water depth (r = 0.72, n = 30,

P>0.001) (Appendix A).

Geochemical Results

Organic matter concentration in 30 surface sediment samples from Lake Charles ranged

from 0.0% (i.e. pure quartz sand) to 38.4%. OM content is positively correlated with water

depth (r = 0.44, n = 30, P<0.05) (Appendix A).

Ra-226 vs. Geochemical Results

Radium-226 activity in surface sediments from Lake Charles is positively correlated with

organic matter content (r = 0.77, n = 30, P>0.001) (Figure 4-1).

Study Lake Sediment Cores

Radioisotopic Results

Radium-226

Cores from the groundwater-augmented lakes all display upcore increases in 226Ra activity

(Figure 4-2). Surface sediments (0-4 cm) possess about an order of magnitude more 226Ra

activity than do deeper sediments. Topmost samples range in 226Ra activity from 7.6 dpm g1 in

Little Hobbs Lake to 44.9 dpm g1 in Lake Charles. Surface sediments exceed 5 dpm g-1, a value

suggested by Brenner et al. (2004) as indicative of anthropogenic 226Ra enrichment.

Stratigraphic distribution of 226Ra in the cores indicates that enrichment occurred recently.

Several depths in the Lake Charles core possess 226Ra activities >30 dpm g1 and are the

highest values yet reported for a Florida lake sediment core. Radium-226 activity in the Lake









RADIUM-226 ACCUMULATION IN SEDIMENTS OF GROUNDWATER-AUGMENTED
LAKES IN HILLSBOROUGH COUNTY, FLORIDA, USA




















By

BRANDY SUNSHINE DE ARMOND


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA




2007









Saddleback sediment core ranges from 0.25 mg g-1 to 190.3 mg g-1, and sharply decreases below

the 16 cm sample (84.6 mg g-) (Appendix A). Lake Crystal's calcium concentration exhibits a

narrow range, from 0.0 mg g-1 to 0.59 mg g-1 (Appendix A). Calcium concentration in Little

Hobbs Lake ranges from 0.0 mg g-1 to 2.3 mg g-1 (Appendix A).

Total phosphorus

Total P concentration in the Lake Charles core varies from 0.51 mg g1 in the 20-24 cm

sample to 0.82 mg g1 in the surface sediment sample (0 4 cm) (Figure 4-3 C). The sediment

core from Lake Saddleback has a Total P concentration ranging from 0.33 mg g1 to 0.67 mg g-

(Appendix A). Total P concentration in the Lake Crystal core varies from 0.03 mg g1 to 1.12

mg g1 (Appendix A). Total P concentration in Little Hobbs Lake ranges from 0.05 mg g1 to

1.91 mg g1 (Appendix A).

Ra-226 vs. Geochemical Results

Radium-226 stratigraphy in each core was compared with the stratigraphic distribution of

other geochemical variables (organic matter [OM], calcium [Ca], magnesium [Mg], and total

phosphorus [P]) to explore the mode of radium delivery to the lakes. Previous studies of Florida

lakes showed a strong correlation between sediment total P and 226Ra, suggesting both were

delivered by a common mechanism. It was proposed that colluvial or aeolian processes had

delivered phosphate-rich, Ra-containing particles to the lakes (Brenner et al. 1994, 1997). Study

of groundwater-augmented Round Lake, however, showed a strong correlation between 226Ra

activity and both inorganic (carbonate) carbon and Ca in sediment cores. This suggested that

bicarbonate-rich groundwater was the source of 226Ra entering Round Lake (Brenner et al. 2000).

High levels of 226Ra in Round Lake biota also pointed to a dissolved source of the radionuclide.

Sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal show a strong

stratigraphic correlation between 226Ra and Ca concentrations (Table 4-1, Figure 4-4 A). Among











Lake Crystal Core Activity (dpm/g)


0 5 10 15


Figure 4-3. Continued












Appendix A-2. Data from sediment cores taken in Lakes Charles, Crystal, Little Hobbs, and
Saddleback.


Corrected Mean
Ra-226 Activity
(dpm g 1)


Sample
Depth
(cm)


Lake

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles

Charles


Pb-210 Cs-137 Cs-137


Corrected
o Ra-226
Activity

3.1

2.1

2.9

2.2

3.9

0.4

1.7

2.4

2.2

1.6

1.4

1.2

1.2

2.0

0.4

0.4

0.9

0.2

0.3

1.0

0.6

0.6

0.2

0.4

0.2

0.3

0.2

0.4

0.2


Pb-210
(dpm g ')

34.2

35.4

39.2

34.0

38.3

18.0

28.0

32.1

28.2

22.7

25.4

21.5

17.5

15.9

14.0

11.9

12.5

13.6

12.5

15.4

13.1

11.9

8.7

9.5

10.3

8.8

10.6

1.4

2.2


Error

0.9

0.9

0.8

0.9

0.9

0.5

0.6

0.7

0.4

0.5

0.8

0.6

0.5

0.5

0.4

0.3

0.5

0.4

0.4

0.4

0.4

0.2

0.3

0.2

0.3

0.3

0.3

0.1

0.1


(dpm g-')

1.1

1.0

1.0

0.9

1.3

1.3

2.5

2.6

2.7

3.2

4.0

3.9

4.4

3.9

5.6

7.1

7.3

8.1

8.2

9.0

9.1

9.5

9.6

9.1

6.7

5.1

5.0

1.6

1.1


Error

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.2

0.1

0.1

0.1

0.1

0.1

0.2

0.2

0.2

0.2

0.2

0.1

0.2

0.1

0.1

0.1

0.1

0.0

0.1











Little Hobbs Lake Core
Activity (dpmlg)

0 5 10 15 20


0

10


20

30

40


50

60


70

80

90


100


Figure 4-3. Continued


25 30









lakes, the correlation is weakest in Lake Charles (r = 0.82), but is nonetheless strong (p<0.001).

The Lake Charles core does not display a significant correlation between 226Ra and total P over

its entire length, but 226Ra and total P are highly correlated in the top 52 cm (r = 0.68, p<0.01),

where 226Ra activity increases abruptly. Radium-226 activity and OM content are positively

correlated throughout the Charles core and this correlation is stronger (r = 0.89, p<0.001) when

only the topmost sediments (0-52 cm) are considered (Figure 4-4 B).

In the Crystal Lake core, the only variable significantly correlated with 226Ra activity was

Ca (r = 0.94, p<0.001) (Table 4-1). In the Little Hobbs core, Ca, Mg, P, and OM were positively

correlated with 226Ra at p<0.01 or p<0.001 (Table 4-1). The Saddleback core displays a very

strong positive correlation between Ca and 226Ra (r = 0.99, p<0.001), as well as between Mg and

226Ra (r = 0.95, p<0.001) (Table 4-1). The correlation between 226Ra and P is weaker, but

significant (r = 0.69, p<0.05). Radium-226 activity in the Saddleback core shows a strong

negative correlation with organic matter. Strontium was measurable in the Charles and

Saddleback sediments. In the Saddleback deposits, Sr concentrations were highest in near-

surface sediments and highly correlated with 226Ra (r = 0.98, p<0.001). In the Lake Charles core,

highest Sr concentrations were associated with recent sediments, with the exception of a single

peak at 104-108 cm. Excluding this sample, Sr concentrations and 226Ra activities are strongly

correlated (r = 0.68, p<0.001).

Radium-226 activity is positively correlated with OM content in the core (r = 0.57, n = 24,

P<0.1). Radium-226 activity is also positively correlated with calcium concentration in the

sediment core (r = 0.80, n = 24, p<0.001), but is not significantly correlated with TP

concentration.










APPENDIX
DATA

Appendix A-i. Data from Lake Charles Sediment Samples.
Ra-226
Water Depth Activity a Ra-226
(m) TYPE (dpm g1) Activity %OM
0.00 Transect 1 7.5 1.4 14.3
0.31 Transect 1 2.9 0.5 9.1
0.91 Transect 1 10.7 2.0 38.4
1.83 Transect 1 8.9 0.9 25.6
0.00 Transect 2 0.6 0.8 0.0
0.31 Transect 2 0.6 0.4 1.3
0.91 Transect 2 10.5 1.2 28.9
1.83 Transect 2 15.8 1.2 16.8
0.00 Transect 3 4.6 0.6 19.0
0.31 Transect 3 1.5 0.7 6.9
0.91 Transect 3 2.3 0.3 4.7
1.83 Transect 3 10.6 0.9 16.8
0.00 Transect 4 3.0 0.1 6.4
0.31 Transect 4 3.5 0.5 0.0
0.91 Transect 4 12.3 0.9 25.7
1.83 Transect 4 7.8 1.4 9.4
0.00 Transect 5 2.8 0.2 4.6
0.31 Transect 5 3.0 0.2 3.5
0.91 Transect 5 8.1 0.3 19.8
1.83 Transect 5 8.5 3.4 25.5
2.40 Deep Surface Grab 11.3 2.1 21.4
4.70 Deep Surface Grab 14.7 0.9 15.5
2.60 Deep Surface Grab 12.9 11.7 28.6
3.00 Deep Surface Grab 8.8 2.5 11.0
1.20 Deep Surface Grab 12.8 1.6 27.1
2.00 Deep Surface Grab 16.5 1.0 22.3
1.30 Deep Surface Grab 11.3 0.2 24.3
1.85 Deep Surface Grab 11.9 0.7 25.2
2.55 Deep Surface Grab 15.6 0.6 23.8
2.50 Deep Surface Grab 23.9 0.9 32.1

Note: m = meters, dpm g-1 = decays per minute per gram, a = standard deviation, %OM =
percent organic matter, Ra-226 Corrected Mean Activity and Corrected Standard Deviations are
given.









displayed values of 17.5 and 44.9 dpm g-1, respectively. The 226Ra values are much greater than

those measured in lakes and wetlands that receive most of their hydrologic input from surface

waters (Brenner et al. 1999, 2001, 2004). High activities were measured previously in surface

deposits of groundwater-augmented Round Lake (26.9 and 26.8 dpm g-l) (Brenner et al. 2000),

and in topmost sediments from Lake Rowell (18.4 dpm g-1). Although Lake Rowell is not

deliberately augmented, it is now suspected that it, too, may receive substantial 226Ra in

groundwater inputs from water pumped for mining and domestic use.

Pumped Floridan Aquifer water is probably the source of much 226Ra activity in sediment

cores from the study lakes. Several lines of evidence implicate augmentation water. First, the

210Pb and 226Ra stratigraphies show the increase in 226Ra occurred recently, probably within the

last few decades. Second, deep groundwaters in the region contain appreciable 226Ra.

Augmentation water entering the study lakes ranges from 0.82 dpm 1-1 (Little Hobbs) to 3.26

dpm 1- (Saddleback). Third, there is 226Ra/210Pb disequilibrium at depths in the Charles, Crystal,

and Saddleback cores. This suggests that 226Ra enters the lakes in dissolved form, separated

from its precursors and not yet equilibrated with its daughters. Fourth, all four cores show a

strong stratigraphic correlation between 226Ra and Ca, and both elements are recent additions to

the sediment. Groundwater is rich in calcium bicarbonate and was added to the lakes in

substantial quantity only with the onset of augmentation. Fifth, greater Sr in the recent deposits

of Charles and Saddleback lakes also indicates groundwater input. Strontium concentrations in

limestone are high compared to concentrations in the surficial quartz sands that surround the

lakes. Although augmentation water is the probable source of 226Ra that reaches the lake

sediments, recent increases in 226Ra have also been detected in cores from Florida lakes that do

not receive deliberate augmentation (Brenner et al. 2004). Groundwater input may also be the











Appendix A-2. Continued


Sample Corrected Mean Corrected o
Depth Ra-226 Activity Ra-226 Pb-210 Pb-210 Cs-137 Cs-137
Lake (cm) (dpm g-) Activity (dpm g') Error (dpm g') Error

Little Hobbs 4 7.6 0.3 25.9 0.4 3.0 0.1

Little Hobbs 8 7.5 0.4 26.0 0.3 3.4 0.1

Little Hobbs 12 7.8 0.4 24.4 0.4 3.5 0.1

Little Hobbs 16 8.0 0.1 20.7 0.5 4.3 0.1

Little Hobbs 20 8.5 0.9 21.1 0.5 4.7 0.1

Little Hobbs 24 7.7 0.4 18.5 0.3 4.9 0.1

Little Hobbs 28 6.7 0.6 16.7 0.4 4.4 0.1

Little Hobbs 32 6.7 0.7 13.5 0.4 2.2 0.1

Little Hobbs 36 6.4 0.9 13.3 0.4 1.9 0.1

Little Hobbs 40 5.3 0.6 13.3 0.5 1.0 0.1

Little Hobbs 44 4.9 0.1 11.0 0.3 1.3 0.0

Little Hobbs 48 4.5 0.2 10.0 0.4 1.4 0.1

Little Hobbs 52 3.5 0.2 11.0 0.3 1.0 0.0

Little Hobbs 56 3.2 0.1 9.1 0.2 0.7 0.0

Little Hobbs 60 2.5 0.3 6.3 0.2 0.6 0.0

Little Hobbs 64 2.1 0.4 4.2 0.2 0.5 0.0

Little Hobbs 68 1.2 0.3 4.3 0.2 0.4 0.0

Little Hobbs 72 1.2 0.3 0.3 0.1 0.2 0.0

Little Hobbs 76 0.4 0.0 0.4 0.0 0.1 0.0

Little Hobbs 80 0.4 0.0 1.0 0.1 0.0 0.0

Little Hobbs 84 0.5 0.2 0.4 0.0 0.0 0.0

Little Hobbs 88 0.3 0.2 -0.3 0.0 0.0 0.0









impacts, including the accumulation of 226Ra in sediments and aquatic food webs, and the

alteration of diatom communities. Preliminary findings also suggested potential human health

risks. Analysis of data from the Round Lake study indicated regular consumption of Unionid

mussels from that basin would likely raise cancer mortality and morbidity risk above the

acceptable range (Hazardous Substance and Waste Management Research, Inc. 2000). Cancer

risk might also increase if augmented lakes were allowed to desiccate and sediments became

exposed, thereby increasing the probability of ingestion, inhalation, and external exposure to

alpha emitters (Hazardous Substance and Waste Management Research, Inc. 2004).

Objectives

Population growth in Hillsborough County is steadily increasing. Lake augmentation will

probably be maintained to avoid water body desiccation and to prevent human exposure to alpha

emitters. Given the potential environmental effects of groundwater augmentation, I decided to

analyze surface sediments and sediment cores from four groundwater-augmented lakes in

Hillsborough County, Florida, USA (Charles, Saddleback, Little Hobbs, and Crystal) (Figures 1-

1 through 1-5).

My objectives were to:

* assess the geochemical effects of long-term augmentation on lake sediments

* identify the sediment fraction that binds dissolved 226Ra in groundwater after it enters the
lake

* evaluate the areal and stratigraphic distribution of 226Ra and other constituents in surface
sediments and sediment profiles to better understand the mechanism of Radium delivery to
the lakes

* determine if radium in sediments had entered the lake in particulates, indicating erosional
input, as had previously been speculated (Brenner et al. 1997), or if it had been delivered to
lakes in soluble form with augmentation water








Florida N


30000'N

29 00O'N
Gulf of
Mexico k 2oo'N

27000'N
SCALE
0 100 km


Figure 1-1. Map of the state of Florida with the star showing the approximate location of the
study lakes, northwestern Hillsborough County.









CHAPTER 2
BACKGROUND

Radium Chemistry

Radium, one of the elements discovered by the Curies in 1898, is an alkaline-earth

element, and the heaviest natural Rare Earth Element (Vdovenko and Dubasov 1975). A 2+

cation, Ra behaves much like Barium (Ba) (Vdovenko and Dubasov 1975), and Ca (Mirka et al.

1996). There are 13 known radium isotopes, none of which are stable (Vdovenko and Dubasov

1975). The isotope 226Ra is a product of the 238U decay chain (Figure 2-1) and 222Rn gas is a

daughter product of 226Ra (Kaufmann and Bliss 1977; Vdovenko and Dubasov 1975). Radium-

226 is an alpha emitter with accompanying gamma radiation and a long half life (1620 years)

(Vdovenko and Dubasov 1975; Scott 1997).

Radium Health Concerns

Radium-226 is cause for concern because it has a long half life, it can substitute for

calcium in bone tissue and it emits alpha and gamma radiation (Mirka et al 1996). Alpha

particles are generally only harmful if emitted inside the body (i.e., through ingestion or

inhalation), while both internal and external exposure to gamma radiation is harmful (USEPA

2007). Both types of radiation may cause damage to tissues, and could result in bone tumors

osteosarcomaa), leukemia, and other carcinomas (Mirka et al 1996; Scott 1997). Ninety-five to

ninety-nine percent of the 226Ra that enters bone tissue will remain in the tissue (Vdovenko and

Dubasov 1975). Radon-222 gas, also a known carcinogen, is a daughter product of 226Ra.

Radium-226 in the Floridan Aquifer

The waters of the Floridan aquifer, the main source of drinking water for Hillsborough

County, Florida, can contain Radium-226. It is the product of the weathering of 238U-rich

carbonate-fluorapatite deposits in the bedrock (Kaufmann and Bliss 1977; Upchurch and



































Figure 1-4. An aerial image of Crystal Lake (north and south), with U.S. 41 to the east.












Appendix A-2. Continued


Calcium
Concentration
(mg/g)


Magnesium
Concentration
(mg/g)


Strontium
Concentration
(mg/g)


Total Phosphorus
(mg/g)


Lake

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal


Sample
Depth
(cm)

4

8

12

16

20

24

28

32

36

40

44

48

52

56

60

64

68

72

76

80

84

88

92

96

100

104

106


%OM

26.9

26.0

29.4

38.8

41.3

45.9

45.6

34.7

24.9

24.9

18.9

19.8

32.5

34.5

35.6

20.4

9.2

7.9

5.0

3.6

3.0

2.9

8.1

0.0

0.0

0.0

0.0
















0.5
0





20



E

S40 -
0

















100 -
,m

'- 60
a-
a



80






100-


Lake Charles Core
Total phosphorus (mglg)

0.6 0.7 0.8
1 1 1


Figure 4-4. Continued









ACKNOWLEDGMENTS

For helping to foster the love of the world around me, I thank Mrs. Burwell, my grade

school gifted science teacher who lived on our street and would let me gaze at the moon through

her telescope. I thank my advisor, Dr. Mark Brenner, for his continual support and music

recommendations. The Southwest Florida Water Management District and the University of

Florida Land Use and Environmental Change Institute (LUECI) funded this project. I thank Dr.

Jason Curtis for his assistance and use of his garage, William Kenney for his collaboration and

encouragement, and Byron Shumate for his unflappable positive attitude. I appreciate Doug

Leeper from the Southwest Florida Water Management District for his willingness to "get his

feet wet." I am grateful to Elizabeth Hamilton, Amelia Evensen, Gianna Brown, and Xin Wang

for making bearable the grueling task of sifting through sediments. I also have much gratitude

for the support and friendship of Susan Tiemey (nee Kulp) throughout my graduate experience.









LIST OF FIGURES


Figure page

1-1. Map of the state of Florida with the star showing the approximate location of the study
lakes, northwestern Hillsborough County............................. .................20

1-2. An aerial image of Hillsborough County, Florida...................................... ...... ............... 21

1-3. An aerial view of Lakes Charles (southeast corner) and Saddleback Lake (just west of
center). Round Lake, also mentioned in the text, is located just west of Saddleback
Lake. The lakes are bounded by Dale Mabry Highway (C.R. 597) to the west and
V an D yke R oad to the north. ..................................................................... ..................22

1-4. An aerial image of Crystal Lake (north and south), with U.S. 41 to the east......................23

1-5. An aerial image of Little Hobbs (Lutz) Lake, just west of U.S. 41....................................24

2-1. The decay of Uranium-238 to stable Lead-206. .................................................26

4-1. Scatter plot showing the relation between organic matter concentration and 226Ra
activity in surface sediments from Lake Charles (r = 0.77)............... ...............34

4-3. Radionuclide (226Ra, 210Pb, 137Cs) activities (in dpm g-l) in sediment cores from
groundwater augmented study lakes. A) Lake Charles. B) Lake Saddleback. C) Little
H obbs L ake. D ) C crystal L ake. ................................................................... ..................35

4-4. Concentrations in the Lake Charles sediment core of: A) Organic matter versus depth.
B) Total phosphorus versus depth. C) Calcium concentration versus depth ....................39

4-5. Scatter plots showing the relation between: A) Organic matter concentration and 226Ra
activity in the Lake Charles sediment core (r = 0.57). B) Calcium concentration and
226Ra activity in the Lake Charles sediment core (r = 0.80). ...........................................42









source for 226Ra in these lakes, but may be pumped to the surface for other reasons, including

crop irrigation, residential, mining, and industrial uses, after which it runs off into local water

bodies.

In most Florida lake sediment cores that display an upcore increase in 226Ra activity, the

change is rather continuous over the uppermost deposits, reaching highest activities in surface or

near-surface layers. There are several possible explanations for this smooth trend. First, since

the onset of groundwater input, there may have been a steady increase in the amount of

groundwater reaching the lakes. This may be true for Florida lakes with watersheds that have

been subject to increasing development over the last century, such as those in Hillsborough

County, but it is an unlikely explanation for this trend in groundwater-augmented systems. The

latter group of lakes has received groundwater supplements at varying rates over the years,

depending on rainfall amount and the need for augmentation. The pattern of 226Ra distribution in

the sediments of groundwater-augmented lakes may reflect, in part, downward transport and

adsorption of dissolved 226Ra on the sediment lens, with most 226Ra adhering to near-surface

deposits. Florida lakes can lose a substantial amount of water to downward leakage (Deevey

1988) and augmented lakes are especially "leaky" (Metz and Sacks 2002), hence their need for

groundwater supplements. This downward transport of 226Ra may also explain why the initial

rise of 226Ra activity in cores may appear in sediments deposited prior to the onset of

groundwater augmentation.

Sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal display

geochemical changes in their uppermost deposits. Cores from all four lakes show upcore

increases in 226Ra activity, Ca, and Mg content. The Charles and Saddleback cores display a

general increase in Sr concentration. The recent geochemical and biological changes in the









Charles core varies from 7.2 dpm g-1 in the 88-92 cm sample to 44.9 dpm g1 in the topmost

sample (0-4 cm).

Lead-210

Total 210Pb activity in the Lake Charles core ranges from 8.7 to 39.2 dpm g-1, with higher

values recorded in the upper portion of the core (Figure 4-2 A).

Isotopic disequilibrium (226Ra/210Pb) is apparent at depths in the Charles, Saddleback, and

Crystal cores where 226Ra activity exceeds total 210Pb activity (Figure 4-2 A, B, D). This

suggests the lakes received dissolved 226Ra that separated from its parent isotopes (e.g., 238U) and

did not yet equilibrate with its daughters (e.g., 210Pb). Disequilibrium is most obvious in shallow

deposits of the Charles and Saddleback cores where 226Ra is greater than total 210Pb. In these

recent sediments, 226Ra activity exceeds the combined activities of supported and unsupported

(excess) 210Pb, indicating the presence of significant 226Ra without its daughters.

Geochemical Results

Organic matter

The organic matter concentration in the Lake Charles sediment core ranges from 25.8% to

43.3%. Organic content is inversely correlated with depth in the sediment core (r = -0.58, n =

24, P<0.01) (Figure 4-3 A).

The organic matter concentrations in Lakes Saddleback, Crystal, and Little Hobbs

sediment cores range from 29.4% to 66.4%, 0% to 45.9%, and 2.76% to 59.3%, respectively

(Appendix A).

Calcium

The calcium concentrations in all four lake sediment cores were generally greater in the

upper half of the cores (Figure 4-3 B). Calcium concentration in the Lake Charles sediment core

ranges from 0.54 mg g-1 to 10.06 mg g-1 (Appendix A). Calcium concentration in the Lake

































2007 Brandy Sunshine DeArmond









LIST OF TABLES


Table page

4-1. Correlation coefficients (r) of stratigraphic correlation between 226Ra activity and
concentrations of calcium (Ca), magnesium (Mg), total phosphorus (P), strontium
(Sr), and organic matter (OM) in sediment cores from Lake Charles, Saddleback,
Little Hobbs, and Crystal. ...................................... ..... ......... .... ............33

A-1. Data from Lake Charles Sediment Samples. ............................................. ............... 48

A-2. Data from sediment cores taken in Lakes Charles, Crystal, Little Hobbs, and
Saddleback ................................................................................49









CHAPTER 3
METHODS

Sampling

Surface Sediments

Shoreline and shallow-water samples from Lake Charles were collected by hand.

Sediments from deeper water were obtained with an Ekman dredge. Surface sediments were

collected from 30 sites throughout Lake Charles, from the shoreline to a maximum water depth

of -4.7 m. Sediment samples were placed in pre-weighed, pre-labeled plastic containers for

transport to the laboratory. In the laboratory, wet sediment was weighed, freeze-dried, re-

weighed and ground with a mortar and pestle for radionuclide, nutrient, and cation analyses.

Sediment Cores

Sediment cores were collected in 2003 from Lake Charles, Saddleback, Little Hobbs, and

Crystal from the deepest part of the lakes using a sediment-water interface piston corer designed

to collect undisturbed sediment/water interface profiles (Fisher et al. 1992). Cores were taken in

areas with substantial sediment accumulation and minimal sand content. They were sectioned in

the field at 4-cm intervals in a vertical position. Sediments were extruded into a tray and

samples were placed in pre-weighed, pre-labeled plastic containers for transport to the

laboratory. In the laboratory, wet sediment was weighed, freeze-dried, re-weighed and ground

with a mortar and pestle for radionuclide, nutrient, and cation analyses.

Determination of Radioisotope Activity

Total 210Pb, 226Ra, and 137Cs activities were measured in contiguous samples from the

mud/water interface to depths where total 210Pb and 226Ra activities were low and similar to one

another. Core samples in Lake Charles were analyzed to a depth of 96 cm. Radium-226 was

also measured in surface sediment samples from Lake Charles. Tared SarstedtTM tubes were









BIOGRAPHICAL SKETCH

Brandy Sunshine DeArmond was born on January 10, 1978, in Leesburg, Florida.

Relocating to the Tampa area when she was a toddler, Brandy, the oldest of seven brothers and

sisters, graduated from Hillsborough High School in 1996, where she was part of the swim team,

French Club, and other extra-curricular activities. She traveled to France in 1995 as part of an

exchange program, and held an after-school job at a natural foods store so she could buy her first

car, a bright orange AMC Gremlin. While attending the University of South Florida, where she

graduated in 2001 with a bachelor's degree in geology, she held an internship with the Water

Resources Division of the United States Geological Survey in Tampa. After graduating, she

moved to Gainesville, Florida, where she attended graduate school at the University of Florida,

as part of the Department of Geological Sciences. While in Gainesville, she also attended many

concerts at local venues, dabbled in art and playing the drums, consorted and cavorted with her

best friend Liz, and rode her clunky old bicycle as much as she could. In July 2004, she moved

back to Tampa to work for an environmental consulting company, where she has performed field

work in Florida and Georgia, completed contaminant delineation and remediation, and has also

served as support for expert witnesses in litigation cases. In June 2007, her company transferred

her to Golden, Colorado, where she and her boyfriend, Jason, enjoy camping in the beautiful

Rocky mountains, fossil hunting, collecting rocks, listening to records, and exploring the

multitude of local microbrews. She is currently looking forward to her first real winter and

learning how to snowboard.









Scott TM (1997) Miocene to Holocene history of Florida. In: Randazzo, AF & Jones, DS (eds.):
The geology of Florida: pp 57-67. University Press of Florida, Gainesville.

Stewart JW, Hughes GH (1974) Hydrologic consequences of using ground water to maintain
lake levels affected by water wells near Tampa, Florida. USGS Survey Report of
Investigations No 74. Florida DNR, Tallahassee.

Smoak JM, Krest JM (2006) Source of radium in a well-water-augmented Florida Lake. J.
Environmental Radioactivity. 89:102-114.

Upchurch SB, Randazzo AF (1997) Environmental geology of Florida. In: Randazzo AF, Jones
DS (eds) The geology of Florida: pp 217-249. University Press of Florida, Gainesville FL.

United States Census Bureau, Population Division: Table 1: Annual Estimates of the Population
for Counties of Florida: April 1, 2000 to July 1, 2005 (CO-EST2005-01-12), March 16, 2006.















Lake Charles Core
Organic Matter (% LOI)
25 30 35 40
0 -


10


20


30

so

E
. 50
U)

r 60
Cl
0 o


Figure 4-4. Concentrations in the Lake Charles sediment core of: A) Organic matter versus
depth. B) Total phosphorus versus depth. C) Calcium concentration versus depth.













Lake Charles
Surface Sediments


25



20


0S
E 15
'.
-0

(04
Cu

ir


Organic Matter (%LOI)


Figure 4-1. Scatter plot showing the relation between organic matter concentration and 226Ra
activity in surface sediments from Lake Charles (r = 0.77).


0
a



0 0
0 6

a *


0









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

RADIUM-226 ACCUMULATION IN SEDIMENTS OF GROUNDWATER-AUGMENTED
LAKES IN HILLSBOROUGH COUNTY, FLORIDA, USA

By

Brandy Sunshine DeArmond

December 2007

Chair: Mark Brenner
Major: Geology

I analyzed 226Ra activities in surface sediment samples from Lake Charles, and in sediment

cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal, Hillsborough County, Florida

(USA). The four lakes have received groundwater input from the deep Floridan Aquifer since as

early as the 1960s in order to maintain lake levels. Surface sediments from Lake Charles were

analyzed for organic matter and radionuclide (Radium-226, Lead-210, Cesium-137) activities.

Cores from the four study lakes were analyzed for stratigraphic changes of organic matter,

phosphorus, radionuclides (226Ra, 210Pb, 137Cs), and cations (Calcium, Magnesium, and

Strontium).

Organic matter concentration in 30 surface sediment samples from Lake Charles ranged

from 0.0% (i.e. pure quartz sand) to 38.4%. Organic matter content was positively correlated

with water depth (r = 0.44, n = 30, P<0.05). Radium-226 activities in surface sediments ranged

from 0.6 dpm g-1 to 23.9 dpm g-1. Activities in surface deposits increased with greater water

depth (r = 0.72, n = 30, P<0.01). Radium-226 activity was positively correlated with organic

matter content (r = 0.77, n = 30, P<0.001). Surface sediment samples from Lake Charles

represent material deposited recently, probably since the initiation of hydrologic augmentation.

Radium-226 in these topmost deposits is associated primarily with organic matter. Sediments in









Lake Charles Core
Activity (dpm/g)
0 10 20 30 40 50


0




20

E
U

S40


a0
60
-I-I



80




100


Figure 4-3. Radionuclide (226Ra, 210Pb, 137Cs) activities (in dpm g-') in sediment cores from
groundwater augmented study lakes. A) Lake Charles. B) Lake Saddleback. C) Little
Hobbs Lake. D) Crystal Lake.









groundwater augmentation. Inadvertent addition of deep groundwater associated with past

agriculture and residential development in the watershed also might have contributed to changes

that are evident in the sediment record.









CHAPTER 5
DISCUSSION

Lake Charles Surface Sediments

Surface sediment samples from Lake Charles represent material deposited recently,

probably since the initiation of hydrologic augmentation. Radium-226 in these topmost deposits

is associated primarily with organic matter. Sediments in most Florida lakes are composed

principally of quartz sands and organic matter, but possess little inorganic silt and clay. A study

of surface sediments from 34 Florida lakes demonstrated that both calcium and magnesium were

positively correlated with OM content (Brenner and Binford 1986). Radium-226, another

divalent cation, evidently behaves in a similar fashion, adsorbing to the OM fraction in the Lake

Charles surface sediments. Higher 226Ra activities in sediments from deeper-water sites in Lake

Charles may reflect the high concentration of fine organic particles at these deep locations.

Study Lake Sediment Cores

High 226Ra activities (>40 dpm g-) near the top of the Lake Charles core indicate

substantial delivery of the radionuclide during the lake's 35 years of hydrologic augmentation.

The activity measured in the topmost sample (44.9 dpm g-l) is the highest yet measured in a

Florida lake. Radium-226 activities exceed total 210Pb activities at several depths in the core,

indicating there is disequilibrium between the two radionuclides. Lake Charles is one of only

three Florida lakes in which radioisotopic disequilibrium has been demonstrated definitively

(Brenner et al. 2004).

Calcium concentration is relatively low (<2.0 mg g-) below 44 cm depth in the Lake

Charles core, but increases above that depth. The higher calcium concentrations in uppermost

sediments reflect the recent delivery of Ca in bicarbonate-rich groundwater. Up-core increase in

Ca concentration was also documented in nearby Round Lake, which has been augmented with











Appendix A-2. Continued


Sample Corrected Mean
Depth Ra-226 Activity
(cm) (dpm E 1)


Corrected o
Ra-226
Activity

1.7

1.2

0.9

1.3

0.1

0.2

0.4

0.3

0.4

0.2


Pb-210
(dpm g ')

19.1

18.5

10.2

7.5

4.2

1.8

1.4

1.3

1.8

0.8


Pb-210 Cs-137 Cs-137
Error (dpm g') Error

0.6 1.7 0.1

0.6 1.7 0.1

0.3 2.2 0.1

0.4 2.6 0.1

0.2 1.8 0.1

0.2 1.7 0.1

0.2 1.2 0.1

0.1 1.0 0.1

0.1 1.0 0.0

0.1 0.8 0.0


Lake

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback









Floridan Aquifer water since 1966 (Brenner et al. 2000). Strong stratigraphic correlation

between Ca concentration and 226Ra activity (r = 0.80) suggests that both ions are delivered via

the same process, namely groundwater input. Though Ca concentration and 226Ra activity

correlate, some radium may make its way to the sediment bound in carbonate. High amounts of

226Ra were shown to have been incorporated into the calcium carbonate shells of snails and

mussels that inhabit augmented lakes (Brenner et al. 2000, 2007).

There is no significant correlation between TP and 226Ra in the Lake Charles sediment

core, contrary to findings in several Florida lakes. In 12 cores from eight other Florida lakes, TP

and 226Ra showed strong stratigraphic correlation (Brenner et al. 1997). It was suggested that the

two elements were delivered to the lakes with erosional or aeolian particulate material.

Groundwater entering Lake Charles has a 226Ra activity of 3 dpm L-1, well below the

drinking water standard. The dissolved radionuclide adsorbs to organic matter particles that

accumulate on the lake bottom. Consequently, 226Ra activity in recent sediments can be high.

Previous investigations show that input of dissolved 226Ra to lakes has biological implications.

For instance, bivalves from Round Lake were shown to accumulate high levels of 226Ra in their

tissues (Brenner et al. 2000). A mussel sample (Elliptio buckleyi) from Lake Charles yielded the

highest 226Ra activity yet measured from pelecypods in a Florida lake (619 dpm g-l) (Brenner et

al. 2007). Other infaunal organisms, such as chironomid larvae and oligochaetes, may also be

exposed to high 226Ra activities in surface deposits and may bioaccumulate the radionuclide.

Sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal all show recent

enrichment with 226Ra. Radium-226 activities in surface sediments are about an order of

magnitude greater than "baseline" activities in the deepest levels of the cores. Topmost (0-4 cm)

samples in all four cores had 226Ra activities >5 dpm g-1, and Lakes Saddleback and Charles
































I thank my parents, grandparents, siblings, and best friends Liz and Jason.











Appendix A-2. Continued






Sample Calcium Magnesium Strontium Total
Depth Concentration Concentration Concentration Phosphorus
Lake (cm) %OM (mg/g) (mg/g) (mg/g) (mg/g)


Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback

Saddleback


- standard deviation, Ra-226
Percent organic matter,


190.3

186.7

170.6

84.6

5.2

4.8

4.8

3.9

2.1

1.8

1.2

1.1

1.1

1.1

0.9

0.9

0.9

0.7

0.7

0.5

0.5

0.4

0.3

0.3


Saddleback 100 43.7 0.3 0.6
Note: cm = centimeters, dpm g-1 = decays per minute per gram, a
= Radium-226, Pb-210 = Lead-210, Cs-137 = Cesium-137, %OM
mg/g = milligrams per gram, nd = non detected
















Lake Charles Core


50


40


E 30


0 20
( I
a: In


- I


U
20


E 30

w20

0
cMu
Cu

S10o


0


25 30 35 40


45 50


Organic matter (% LOI)

Lake Charles Core



*








S= 3.368x11.543, R2 = 0.647
y = 3.368X + 11.543, R2 = 0.647 B


0 2 4 6 8 10 12
Calcium (mg/g)

Figure 4-5. Scatter plots showing the relation between: A) Organic matter concentration and
226Ra activity in the Lake Charles sediment core (r = 0.57). B) Calcium concentration
and 226Ra activity in the Lake Charles sediment core (r = 0.80).


*
Og










y = 1.600x 33.03, R2 = 0.329









G eochem ical R results ................. .................................. ...... ....... .............. 30
O organic m matter ......... .... ............. .................................................................. 30
C a lc iu m ................................................................3 0
Total phosphorus ................................................................ .. ......... 31
Ra-226 vs. Geochemical Results ............... ......... ............... 31
Dating Sediment Cores .................................................................................................. 33

5 DISCU SSION ......... ...... .. ......... ....... ....................... ........ 43

Lake Charles Surface Sedim ents ................................................. ............... 43
Study L ake Sedim ent C ores.....................................................43

A PPEN D IX : D A TA .......................................................48

LIST OF REFEREN CES ............... ........ ............................................................ 57

B IO G R A PH IC A L SK E T C H ................................................................................................... 60





































6










Mg:

mgd:

-1
mg g

mm:

n:

Na:

OM:

P:

r:

SO4:

Sr:

SWFWMD:

TP:

WACALIB:

Zmean:


Magnesium

million gallons per day

milligrams per gram

millimeters

Number of samples

Sodium

Organic Matter

Probability (p-value)

Correlation coefficient

Sulfate

Strontium

Southwest Florida Water Management District

Total Phosphorus

Weighted Averaging Calibration

mean depth









TABLE OF CONTENTS

page

A CK N O W LED G M EN T S ................................................................. ........... ............. .....

LIST O F TA B LE S ......... ..... .............. ................................................................. 7

LIST OF FIGURES .................................. .. ..... ..... ................. .8

A B S T R A C T ......... ....................... ............................................................ 1 1

CHAPTER

1 INTRODUCTION ............... .............................. ............................. 14

Previous Lim nological Studies .......................................................................... ............... 15
A ugm entation and L ake C hem istry ...................................................................... .....15
A ugm entation and L ake B iology..................................................................................15
Augm entation and Radioisotopic Studies ............................................ ............... 16
Potential Ecological and Human Health Risk Factors..........................................................17
O b j e c tiv e s ................... ............ ................................................ ................1 8
S tu d y L ak e s .........................................................................19

2 B A CK G R O U N D ...................... ..... ............................ .. .. ......... .... ...... 25

Radium Chemistry ............ ...................... ............... .. .... ...... ..25
R adium H health C concerns ......... ........................................................................... 25
R adium -226 in the Floridan A quifer ........................................................... .....................25

3 METHODS .........................................27

S a m p lin g ......... ............... .................................................................................................2 7
S u rfac e S ed im en ts ..................................................................................................... 2 7
Sedim ent Cores ............................................................................... ................ ............... 27
Determination of Radioisotope Activity .................. ...... ......... .. ........27
G eo ch em ical E v alu ation ................................................................................................... 2 8

4 R E SU L T S .............. ... ................................................................29

Lake Charles Surface Sedim ents ................................................... ............ .............. 29
R adioisotopic R esu lts ...........................................................................................2 9
G eo ch em ical R e su lts ................................................................................................. 2 9
Ra-226 vs. Geochemical Results .................. ................... .......... .............. ...29
Study L ake Sedim ent C ores........................................................................................29
R adioisotopic R results ................................................................. ............... ... ...29
R a d iu m -2 2 6 ......... .............................. .............................................. .2 9
Lead-210 .................................................. ........... ......... 30
















0 2
0


10


20


30

4o
E
S40
c-

' 50
u'

i 60
CL
70


80


90


100


Lake Charles Core
Calcium (mg/g)

4 6 8 10 12
i 1 1 i i


Figure 4-4. Continued









filled with dry, ground sediment to a height of-30 mm. Sample mass was determined and

recorded and tubes were sealed with epoxy glue and set aside for three weeks to allow 214Bi and

214Pb to equilibrate with in situ 226Ra. Radioisotope activities were measured by gamma

counting, using well-type EG & G ORTECTM Intrinsic Germanium Detectors connected to a

4096 channel, multi-channel analyzer (Schelske et al. 1994). Total 210Pb activity was obtained

from the photopeak at 46.5 keV. Radium-226 activity was estimated by averaging activities of

214Pb (295.1 keV), 214Pb (351.9 keV), and 214Bi (609.3 keV) (Moore 1984). Cesium-137 activity

was determined from the 662 keV photopeak (Krishnaswami and Lal 1978). Activities are

expressed as decays per minute per gram dry sediment (dpm g-1).

Geochemical Evaluation

Organic matter in dry sediments was measured by weight loss on ignition (LOI) at 5500C

for 1 hour (Hfkanson and Jansson 1983). Total phosphorus (TP) was measured using a

Technicon Autoanalyzer II with a single-channel colorimeter, following sediment digestion with

H2SO4 and K2S208 (Schelske et al. 1986). Calcium (Ca), magnesium (Mg), and strontium (Sr)

concentrations in sediments were determined by digesting dry, weighed sediment samples in IN

HC1 (Andersen 1976). Concentrations of Ca, Mg, and Sr in solution were read on a Perkin

Elmer 3100 Atomic Absorption Spectrophotometer. Data are expressed as amount per g dry

sediment.





































figure 1-i. An aerial view ot Lakes Cnaries (southeast comer) and Sadaleoack Lake (Just west
of center). Round Lake, also mentioned in the text, is located just west of Saddleback
Lake. The lakes are bounded by Dale Mabry Highway (C.R. 597) to the west and
Van Dyke Road to the north.




Full Text

PAGE 1

1 RADIUM-226 ACCUMULATION IN SEDI MENTS OF GROUNDWATER-AUGMENTED LAKES IN HILLSBOROUGH CO UNTY, FLORIDA, USA By BRANDY SUNSHINE DE ARMOND A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007

PAGE 2

2 2007 Brandy Sunshine DeArmond

PAGE 3

3 I thank my parents, grandparents, sibli ngs, and best friends Liz and Jason.

PAGE 4

4 ACKNOWLEDGMENTS For helping to foster the love of the worl d around me, I thank Mrs. Burwell, my grade school gifted science teacher who lived on our st reet and would let me gaze at the moon through her telescope. I thank my advisor, Dr. Mark Brenner, for his continual support and music recommendations. The Southwest Florida Water Management District and the University of Florida Land Use and Environmental Change Ins titute (LUECI) funded this project. I thank Dr. Jason Curtis for his assistance and use of his garage, William Kenney for his collaboration and encouragement, and Byron Shumate for his unfla ppable positive attitude I appreciate Doug Leeper from the Southwest Florida Water Manage ment District for his willingness to get his feet wet. I am grateful to Elizabeth Ham ilton, Amelia Evensen, Gianna Brown, and Xin Wang for making bearable the grueling task of sifting through sediments. I also have much gratitude for the support and friendship of Susan Tierne y (ne Kulp) throughout my graduate experience.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES................................................................................................................ .........8 ABSTRACT....................................................................................................................... ............11 CHAPTER 1 INTRODUCTION..................................................................................................................14 Previous Limnological Studies...............................................................................................15 Augmentation and Lake Chemistry.................................................................................15 Augmentation and Lake Biology.....................................................................................15 Augmentation and Radioisotopic Studies.......................................................................16 Potential Ecological and Huma n Health Risk Factors............................................................17 Objectives..................................................................................................................... ..........18 Study Lakes.................................................................................................................... ........19 2 BACKGROUND....................................................................................................................25 Radium Chemistry............................................................................................................... ...25 Radium Health Concerns........................................................................................................25 Radium-226 in the Floridan Aquifer......................................................................................25 3 METHODS........................................................................................................................ .....27 Sampling....................................................................................................................... ..........27 Surface Sediments...........................................................................................................27 Sediment Cores................................................................................................................27 Determination of Radioisotope Activity.................................................................................27 Geochemical Evaluation.........................................................................................................28 4 RESULTS........................................................................................................................ .......29 Lake Charles Surface Sediments............................................................................................29 Radioisotopic Results......................................................................................................29 Geochemical Results.......................................................................................................29 Ra-226 vs. Geochemical Results..............................................................................29 Study Lake Sediment Cores....................................................................................................29 Radioisotopic Results......................................................................................................29 Radium-226..............................................................................................................29 Lead-210...................................................................................................................30

PAGE 6

6 Geochemical Results.......................................................................................................30 Organic matter..........................................................................................................30 Calcium....................................................................................................................30 Total phosphorus......................................................................................................31 Ra-226 vs. Geochemical Results.....................................................................................31 Dating Sediment Cores....................................................................................................33 5 DISCUSSION..................................................................................................................... ....43 Lake Charles Surface Sediments............................................................................................43 Study Lake Sediment Cores....................................................................................................43 APPENDIX: DATA.......................................................................................................................48 LIST OF REFERENCES............................................................................................................. ..57 BIOGRAPHICAL SKETCH.........................................................................................................60

PAGE 7

7 LIST OF TABLES Table page 4-1. Correlation coefficients (r) of stratigraphic correlation between 226Ra activity and concentrations of calcium (Ca), magnes ium (Mg), total phosphorus (P), strontium (Sr), and organic matter (OM) in sediment cores from Lake Charles, Saddleback, Little Hobbs, and Crystal...................................................................................................33 A-1. Data from Lake Ch arles Sediment Samples.........................................................................48 A-2. Data from sediment cores taken in La kes Charles, Crystal, Little Hobbs, and Saddleback..................................................................................................................... ....49

PAGE 8

8 LIST OF FIGURES Figure page 1-1. Map of the state of Flor ida with the star showing the approximate location of the study lakes, northwestern Hillsborough County..........................................................................20 1-2. An aerial image of Hillsborough County, Florida.................................................................21 1-3. An aerial view of Lakes Charles (southeas t corner) and Saddleback Lake (just west of center). Round Lake, also mentioned in the text, is located just west of Saddleback Lake. The lakes are bounded by Dale Mabr y Highway (C.R. 597) to the west and Van Dyke Road to the north..............................................................................................22 1-4. An aerial image of Crystal Lake (north and south), with U.S. 41 to the east........................23 1-5. An aerial image of Little Hobbs (Lutz) Lake, just west of U.S. 41.......................................24 2-1. The decay of Uraniu m-238 to stable Lead-206.....................................................................26 4-1. Scatter plot showing the relation between organic matter concentration and 226Ra activity in surface sediments fr om Lake Charles (r = 0.77)...............................................34 4-3. Radionuclide (226Ra, 210Pb, 137Cs) activities (in dpm g-1) in sediment cores from groundwater augmented study lakes. A) Lake Charles. B) Lake Saddleback. C) Little Hobbs Lake. D) Crystal Lake............................................................................................35 4-4. Concentrations in the Lake Charles sedi ment core of: A) Organic matter versus depth. B) Total phosphorus versus depth. C) Calcium concentration versus depth.....................39 4-5. Scatter plots showing th e relation between: A) Orga nic matter concentration and 226Ra activity in the Lake Charles sediment core (r = 0.57). B) Calcium concentration and 226Ra activity in the Lake Charles sediment core (r = 0.80)..............................................42

PAGE 9

9 LIST OF ABBREVIATIONS 1N HCl: 1 Normal Hydrochloric Acid 137Cs: Cesium-137 210Pb: Lead-210 210Po: Polonium-210 214Bi: Bismuth-214 214Pb: Lead-214 222Rn: Radon-222 226Ra: Radium-226 238U: Uranium-238 A: Area Ba: Barium C: Degrees Celsius Ca: Calcium Cl-: Chloride cm: centimeters dpm g-1: decays per minute per gram H2SO4: Sulfuric Acid ha: hectares HCO3 -1: Bicarbonate IC: Inorganic Carbon K2S2O8: Potassium Persulfate keV: kiloelectron volt LOI: Loss On Ignition m: meters

PAGE 10

10 Mg: Magnesium mgd: million gallons per day mg g-1: milligrams per gram mm: millimeters n: Number of samples Na: Sodium OM: Organic Matter P: Probability (p-value) r: Correlation coefficient SO4: Sulfate Sr: Strontium SWFWMD: Southwest Florida Water Management District TP: Total Phosphorus WACALIB: Weighted Averaging Calibration zmean: mean depth

PAGE 11

11 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science RADIUM-226 ACCUMULATION IN SEDI MENTS OF GROUNDWATER-AUGMENTED LAKES IN HILLSBOROUGH COUNTY, FLORIDA, USA By Brandy Sunshine DeArmond December 2007 Chair: Mark Brenner Major: Geology I analyzed 226Ra activities in surface sediment samples from Lake Charles, and in sediment cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal, Hillsborough County, Florida (USA). The four lakes have received groundwater input from the deep Floridan Aquifer since as early as the 1960s in order to maintain lake le vels. Surface sediments from Lake Charles were analyzed for organic matter and radionuclide (Radium-226, Lead-210, Cesium-137) activities. Cores from the four study lakes were analyzed for stratigraphic changes of organic matter, phosphorus, radionuclides (226Ra, 210Pb, 137Cs), and cations (Calcium, Magnesium, and Strontium). Organic matter concentration in 30 surface sedi ment samples from Lake Charles ranged from 0.0% (i.e. pure quartz sand) to 38.4%. Organic matter content was positively correlated with water depth (r = 0.44, n = 30, P<0.05). Radium-226 activities in surface sediments ranged from 0.6 dpm g-1 to 23.9 dpm g-1. Activities in surface deposits increased with greater water depth (r = 0.72, n = 30, P<0.01). Radium-226 activit y was positively correlated with organic matter content (r = 0.77, n = 30, P<0.001). Surface sediment samples from Lake Charles represent material deposited recently, probably si nce the initiation of hydrologic augmentation. Radium-226 in these topmost deposits is associated primarily with organic matter. Sediments in

PAGE 12

12 most Florida lakes are composed principally of quartz sands and organic matter, but possess little inorganic silt and clay. A study of surface sedi ments from 34 Florida lakes demonstrated that both calcium and magnesium were positively correla ted with OM content. Radium-226, another divalent cation, evidently behaves in a similar fa shion, adsorbing to the OM fraction in the Lake Charles surface sediments. Higher 226Ra activities in sediments from deeper-water sites in Lake Charles may reflect the high concentration of fine organic particles at these deep locations. Top samples (0 cm) from sediment cores ta ken in Lakes Charles, Saddleback, Little Hobbs, and Crystal had 226Ra activities of 44.9, 17.5, 7.6, and 8.5 dpm g-1, respectively, about an order of magnitude greater than values in deep er, older deposits. The surface sample from Lake Charles yielded the highest 226Ra activity yet reported from a Fl orida lake core. Several lines of evidence suggest that gr oundwater augmentation is responsible for the high 226Ra activities in recent sediments: (1) 226Ra activity in cores increased recently, (2) the Charles, Crystal, and Saddleback cores display 226Ra /210Pb disequilibrium at several shallow depths, suggesting 226Ra entered the lakes in dissolved form, (3) co res show recent increases in Ca, which, like 226Ra, is abundant in augmentation groundwater, and (4) great er Sr concentrations are associated with higher 226Ra activities in recent Charles and Saddleback sediments. Sr concentrations in Eocene limestones of the deep Floridan Aquifer are high re lative to Sr concentrations in surficial quartz sands around the lakes. Sediment cores from Lakes Charles, Saddl eback, Little Hobbs, and Crystal display geochemical changes in their uppermost deposits. Cores from all four lakes show upcore increases in 226Ra activity, Ca, and Mg c ontent. The Charles and Saddleback cores display a general increase in Sr concentr ation. The recent geochemical and biological changes in the sediment records are consistent with shifts that might be expected as a consequence of deliberate

PAGE 13

13 groundwater augmentation. Inadvertent addition of deep groundwater associated with past agriculture and residential devel opment in the watershed also might have contributed to changes that are evident in the sediment record.

PAGE 14

14 CHAPTER 1 INTRODUCTION Florida is one of the fastestgrowing states in the United St ates, with the Tampa Bay Area a top contender for population growth. From the year 2000 to 2006, the United States Census Bureau reported an estimated increase in popula tion of 13.2% in the State of Florida, and from 2000 to 2005, Hillsborough County experienced a 12% population increase (U.S. Census Bureau 2006). The new construction of infrastructur e, residential developments, schools, and commercial businesses that accompanies rapid p opulation growth places a strain on aquifers (Stewart and Hughes 1974). The deep Floridan Aquifer, which consists of Eocene to Miocene limestones (Scott 1997), is the major source for human use in west-central Florida, and groundwater from it is withdrawn at well-fields in Hillsborough C ounty, Florida, USA (Figure 1-1). During the year 2000, total fresh groundwater withdrawals from Hillsbor ough County ranged from 100 to 200 million gallons per day (mgd), with 194.86 mgd of that removed from the Floridan Aquifer (USGS 2004). Only five years prior, during 1995, the total groundwater withdrawals were 169.22 mgd, which included withdrawals from the Intermediate and Surficial Aquifers (Marella 1995). Since 1965, public supply groundwater use has increas ed from 18.80 mgd to 61.79 mgd in 1990 and 85.51 mgd in 2000 (Marella 1995 & 2004; SWFWMD 2002 & 2004). The population served by the public water supply in Hillsborough County grew from 370,000 in 1970 to 816,641 in 1990 and 854,750 in 2000 (Marella 2004; SWFWMD 2002). The removal of deep groundwater has increased downward seepage of both shallow gro undwater and surface water, causing local lake level declines. Along with anthr opogenic effects, natura l occurrences play a part in the decline of lake levels. Lake stage decreases were ex acerbated by droughts as well (Stewart and Hughes 1974), and Hillsborough County experienced a major drought in 2000. Some lakeside

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15 homeowners found their lakefront property was steadily increasing as the lake shore retreated. Since the 1960s, some lakefront homeowners have been installing single deep groundwater wells on the shoreline of their lakes to allow them to add groundwater to the lakes, i.e., augmentation. The Southwest Florida Water Management Dist rict (SWFWMD), which was formed during the 1970s, is currently in charge of Hillsborough Countys water resources, and has maintained water levels in some of these augmented lakes with these wells. Previous Limnological Studies Augmentation and Lake Chemistry During the 1970s, a few studies evaluated the effects of augmentation on lake hydrologic budgets and water chemistry (Stewart and Hughes 1974; Martin et al. 1976a; Dooris and Martin 1979). Groundwater inputs altered th e chemistry of lake waters (M artin et al. 1976a; Dooris and Martin 1979). Prior to augmentation, most ar ea lakes were soft and dominated by sodium (Na+), sulfate (SO4 2-), and chloride (Cl-), receiving most of their hydrologic input from rainfall and surface runoff. Augmentation with deep gr oundwater converted water bodies into calcium (Ca2+) bicarbonate (HCO3 -1) systems. Augmented lakes have water column ion concentrations with relative proportions sim ilar to groundwater, and displa y high hardness, bicarbonate concentration, and pH (Martin et al. 1976a). Augmentation and Lake Biology Other investigations explored the biological consequences of augmentation (Dooris et al. 1982; Martin et al. 1976b). Phytoplankton diversity is greater in augmented lakes and positively correlated with water-column inorga nic carbon (IC) concentration (Door is et al. 1982). Martin et al. (1976b) suggested groundwater augmenta tion might promote growth of exotic Hydrilla verticillata The Round Lake study also showed that the radionuclide apparently substitutes for calcium in plant tissues and the shells, bones, and flesh of animals. Accumulation of 226Ra in

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16 sediments and food webs of groundwater-augmente d Florida lakes may prove to be common. Likewise, groundwater pumping for other purposes such as agricu ltural irrigation, residential, and industrial uses, may also contribute 226Ra to Floridas aquatic ecosystems (Brenner et al. 2004). Diatom analysis from a core in Round Lake suggested groundwater augmentation contributed to higher dissolved i on concentrations, slightly incr eased pH, and higher trophic state conditions (Brenner and Whitmore 1999). Diatom studies on the four lakes in this study indicate recent alkalization occurred in all four (Brenner et al. 2006). Lake waters apparently change from pH values in the range of 5-5.8 to pH values in the range of 7.2-8. Ionic content also increased in all four study lakes, as indicated by diatom salinity aut ecological (species ecological) da ta. Both of these changes are consistent with what might be expected from th e addition of groundwaters that are high in base cation content. Trophic state appe ars to have increased in all f our lakes, as demonstrated by weighted-averaging calibration (WACALIB) derived estimates for total limn etic total P based on diatom counts in cores (Brenner et al. 2006). Declines in dystrophic diatoms are probably, in part, a result of augmen tation with clear groundwater (Brenner et al. 2006). Augmentation and Radioisotopic Studies Several factors determine dissolved 226Ra concentrations in Flor ida lake waters and the amount of 226Ra adsorbed to recent sediments: (1) 226Ra activity in pumped groundwater, which is influenced by local geology, (2) rate of groun dwater pumping, (3) propor tional contribution of groundwater to the lakes annual hydrologic budg et, (4) lake water residence time, and (5) mixing of augmented water throughout the lake. Sediment composition, particle size, deposition rate, and the through-flow of 226Ra-rich water may also influence the stratigraphic distribution of 226Ra activity in sediments.

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17 Previous paleolimnological study of groundw ater-augmented Round Lake (A = 5 ha, zmean = 2.4 m) near Tampa, Florida indicated a ugmentation, which began in 1966, increased 226Ra input to the water body (Brenner et al. 2000). The lake receives a bout half its annual hydrologic budget from pumped groundwater. Surface sediment s (0-4 cm) from two Round Lake cores had 226Ra activities of 26.9.0 and 26.8.3 dpm g-1 dry (Brenner et al 2000), the highest 226Ra activities that had been measur ed in Florida lake sediments (Brenner et al. 1994, 1997). These high activities were attributed to inputs of groundwater that is rich in dissolved 226Ra, which adsorbs to near-surface sediments (Brenner et al. 2004). Previous experiments at Saddleback Lake demonstrated that pumped groundwater was the principal source of Ra-226 to the lake (Smoak and Krest 2006). Radium-226 activity in topmost Round Lake sediment samples exceeded total 210Pb activity, indicating disequilibrium between 226Ra and supported 210Pb. This phenomenon had been reported for only one other Florida waterbo dy, Lake Rowell (Brenner et al. 1994). Isotopic disequilibrium in Round Lake was linked to augmentation groundwater that passed through 238Urich carbonate-fluorapatite deposits in th e underlying bedrock (Kaufmann and Bliss 1977; Upchurch and Randazzo 1997). The upper Floridan Aquifer can have 226Ra activities that exceed the drinking water standard of 11 dpm g-1 (Kaufmann and Bliss 19 77). Coastal surface waters off west central Florida that re ceive groundwater inputs display high 226Ra activities (Fanning et al. 1982; Miller et al. 1990). High activities of 210Po, a decay product of 226Ra, have been measured in Florida groundwater (Harada et al. 1989) and some of the highest values have been measured in Hillsborough County (Upchurch and Randazzo 1997). Potential Ecological and Hu man Health Risk Factors Previous studies showed groundwater in Hi llsborough County can contain high levels of dissolved 226Ra. Groundwater augmentation of local la kes was also shown to have ecological

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18 impacts, including the accumulation of 226Ra in sediments and aquatic food webs, and the alteration of diatom communities. Preliminary findings also suggested potential human health risks. Analysis of data from the Round Lake study indicated regular consumption of Unionid mussels from that basin would likely raise can cer mortality and morbidity risk above the acceptable range (Hazardous Substance and Waste Management Research, Inc. 2000). Cancer risk might also increase if augmented lakes we re allowed to desiccate and sediments became exposed, thereby increasing the probability of in gestion, inhalation, and external exposure to alpha emitters (Hazardous Substance and Waste Management Research, Inc. 2004). Objectives Population growth in Hillsborough County is st eadily increasing. La ke augmentation will probably be maintained to avoid water body desic cation and to prevent human exposure to alpha emitters. Given the potential environmental effe cts of groundwater augmentation, I decided to analyze surface sediments and sediment cores from four groundwater-augmented lakes in Hillsborough County, Florida, USA (Charles, Saddl eback, Little Hobbs, and Crystal) (Figures 11 through 1-5). My objectives were to: assess the geochemical effects of longterm augmentation on lake sediments identify the sediment frac tion that binds dissolved 226Ra in groundwater af ter it enters the lake evaluate the areal and st ratigraphic distribution of 226Ra and other constituents in surface sediments and sediment profiles to better unde rstand the mechanism of Radium delivery to the lakes determine if radium in sediments had entered the lake in particulat es, indicating erosional input, as had previously been sp eculated (Brenner et al 1997), or if it had been delivered to lakes in soluble form with augmentation water

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19 I evaluated surface sediments from Lake Char les, and sediment core profiles in Lakes Charles, Saddleback, Crystal, and Little Hobbs (Lake Lutz). The surface sediments were analyzed for organic matter and radionuclide cont ent. The cores from the four lakes were analyzed for stratigraphic changes of or ganic matter, phosphorus, radionuclides (210Pb, 226Ra, 137Cs), and cations (Ca, Mg, Sr). Study Lakes All of the lakes in this st udy are located in northwestern Hillsborough County, in a region of neutral to slightly alkalin e, oligotrophic (lacking in plan t nutrients, with a high oxygen content) to mesotrophic (lakes with an intermedia te level of productivity), clear-water lakes, and on a moderately thick plain of silty sand that overlies Tampa Limestone (Figures 1-1 through 15). Recent analyses by the Florida Department of Health showed 226Ra enters all four basins with groundwater input. Trip licate samples run on augmentation water at Lake Charles, Saddleback, Little Hobbs, and Crystal yielded mean 226Ra concentrations of 3.11, 3.26, 0.82, and 1.41 dpm l-1, respectively. Location (latitude/long itude), surface area, maximum depth, augmentation history, and hydrol ogic setting for the study lakes are summarized below: Lake Charles: 28N, 82W, small (6 ha), shallow (zmax = 5.5 m), augmented since summer 1968, part of the Rocky/Bushy Creek watershed Lake Saddleback: 28, 82, small (12.55 ha), shallow (zmax = 6.71 m), augmented since summer 1968, part of the Rocky/Bushy Creek watershed Crystal Lake: 28, 82 small (6.5 ha), shallow (zmax = 7.9 m), augmented since 1973, part of the Rocky/Bushy Creek watershed Little Hobbs Lake (Lutz Lake): 28 11, 82, small (2.8 ha), shallow (zmax = 5.5m), augmented since the early 1970s, part of the Cypress Creek watershed

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20 Figure 1-1. Map of the state of Florida with th e star showing the appr oximate location of the study lakes, northwestern Hillsborough County.

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21 Figure 1-2. An aerial image of Hillsborough County, Florida.

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22 Figure 1-3. An aerial view of Lakes Charles (sou theast corner) and Saddle back Lake (just west of center). Round Lake, also mentioned in th e text, is located just west of Saddleback Lake. The lakes are bounded by Dale Mabr y Highway (C.R. 597) to the west and Van Dyke Road to the north.

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23 Figure 1-4. An aerial image of Crystal Lake (n orth and south), with U.S. 41 to the east.

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24 Figure 1-5. An aerial image of Little Hobbs (Lutz) Lake, just west of U.S. 41.

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25 CHAPTER 2 BACKGROUND Radium Chemistry Radium, one of the elements discovered by th e Curies in 1898, is an alkaline-earth element, and the heaviest natural Rare Ea rth Element (Vdovenko and Dubasov 1975). A 2+ cation, Ra behaves much like Barium (Ba) (V dovenko and Dubasov 1975), and Ca (Mirka et al. 1996). There are 13 known radium isotopes, non e of which are stable (Vdovenko and Dubasov 1975). The isotope 226Ra is a product of the 238U decay chain (Figure 2-1) and 222Rn gas is a daughter product of 226Ra (Kaufmann and Bliss 1977; Vdovenko and Dubasov 1975). Radium226 is an alpha emitter with accompanying gamma radiation and a long half life (1620 years) (Vdovenko and Dubasov 1975; Scott 1997). Radium Health Concerns Radium-226 is cause for concern because it has a long half life, it can substitute for calcium in bone tissue and it emits alpha and gamma radiation (Mirka et al 1996). Alpha particles are generally only harmful if emitte d inside the body (i.e., through ingestion or inhalation), while both internal and external exposure to gamma radiation is harmful (USEPA 2007). Both types of radiation may cause damage to tissues, and could result in bone tumors (osteosarcoma), leukemia, and ot her carcinomas (Mirka et al 1996; Scott 1997). Ninety-five to ninety-nine percent of the 226Ra that enters bone tissue will remain in the tissue (Vdovenko and Dubasov 1975). Radon-222 gas, also a know n carcinogen, is a daughter product of 226Ra. Radium-226 in the Floridan Aquifer The waters of the Floridan aquifer, the main source of drinking water for Hillsborough County, Florida, can contain Radium-226. It is the product of the weathering of 238U-rich carbonate-fluorapatite deposits in the bedrock (Kaufmann a nd Bliss 1977; Upchurch and

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26 Randazzo 1997). The upper Floridan Aquifer can have 226Ra activities that exceed the drinking water standard of 11 dpm g-1 (Kaufmann and Bliss 1977). Coastal surface waters off west central Florida, south of the Tampa area, that receive groundwater inputs from the surficial and Upper Floridan aquifers, and pass thr ough Hawthorn group sediments, display high 226Ra activities (Fanning et al. 1982; Miller et al. 1990). High 210Po activities have been measured in Florida groundwater (Harada et al. 1989) and some of the highest values have been measured in Hillsborough County (Upchurch and Randazzo 1997). Figure 2-1. The decay of Uranium-238 to stable Lead-206.

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27 CHAPTER 3 METHODS Sampling Surface Sediments Shoreline and shallow-water samples from Lake Charles were collected by hand. Sediments from deeper water were obtained w ith an Ekman dredge. Surface sediments were collected from 30 sites throughout Lake Charles, from the shoreline to a maximum water depth of ~4.7 m. Sediment samples were placed in pre-weighed, pre-labeled plastic containers for transport to the laboratory. In the laborato ry, wet sediment was we ighed, freeze-dried, reweighed and ground with a mortar and pestle fo r radionuclide, nutrient, and cation analyses. Sediment Cores Sediment cores were collected in 2003 from Lake Charles, Saddleback, Little Hobbs, and Crystal from the deepest part of the lakes usi ng a sediment-water interface piston corer designed to collect undisturbed sediment/water interface prof iles (Fisher et al. 1992). Cores were taken in areas with substantial sediment accumulation and mi nimal sand content. They were sectioned in the field at 4-cm intervals in a vertical posit ion. Sediments were extruded into a tray and samples were placed in pre-weighed, pre-labele d plastic containers for transport to the laboratory. In the laboratory, wet sediment was weighed, fre eze-dried, re-w eighed and ground with a mortar and pestle for radionuc lide, nutrient, and cation analyses. Determination of Radioisotope Activity Total 210Pb, 226Ra, and 137Cs activities were measured in contiguous samples from the mud/water interface to depths where total 210Pb and 226Ra activities were low and similar to one another. Core samples in Lake Charles were analyzed to a depth of 96 cm. Radium-226 was also measured in surface sediment samples from Lake Charles. Tared Sarstedt tubes were

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28 filled with dry, ground sediment to a height of ~30 mm. Sample mass was determined and recorded and tubes were seal ed with epoxy glue and set as ide for three weeks to allow 214Bi and 214Pb to equilibrate with in situ 226Ra. Radioisotope activities were measured by gamma counting, using well-type EG & G ORTEC Intr insic Germanium Detectors connected to a 4096 channel, multi-channel analyzer (Schelske et al. 1994). Total 210Pb activity was obtained from the photopeak at 46.5 keV. Radium-226 ac tivity was estimated by av eraging activities of 214Pb (295.1 keV), 214Pb (351.9 keV), and 214Bi (609.3 keV) (Moore 1984). Cesium-137 activity was determined from the 662 keV photopeak (K rishnaswami and Lal 197 8). Activities are expressed as decays per minute per gram dry sediment (dpm g-1). Geochemical Evaluation Organic matter in dry sediments was measured by weight loss on ignition (LOI) at 550C for 1 hour (Hkanson and Jansson 1983). To tal phosphorus (TP) was measured using a Technicon Autoanalyzer II with a single-channel colorimeter, fo llowing sediment digestion with H2SO4 and K2S2O8 (Schelske et al. 1986). Calcium (C a), magnesium (Mg), and strontium (Sr) concentrations in sediments were determined by digesting dry, weighed sediment samples in 1N HCl (Andersen 1976). Concentrations of Ca, M g, and Sr in solution were read on a Perkin Elmer 3100 Atomic Absorption Spectrophotometer. Data are expressed as amount per g dry sediment.

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29 CHAPTER 4 RESULTS Lake Charles Surface Sediments Radioisotopic Results Radium-226 activities in surface sediments in Lake Charles range from 0.6 dpm g-1 to 23.9 dpm g-1. Activities in surface deposits increase with greater water depth (r = 0.72, n = 30, P>0.001) (Appendix A). Geochemical Results Organic matter concentration in 30 surface sedi ment samples from Lake Charles ranged from 0.0% (i.e. pure quartz sand) to 38.4%. OM content is positively correlated with water depth (r = 0.44, n = 30, P<0.05) (Appendix A). Ra-226 vs. Geochemical Results Radium-226 activity in surface sediments from Lake Charles is posi tively correlated with organic matter content (r = 0.77, n = 30, P>0.001) (Figure 4-1). Study Lake Sediment Cores Radioisotopic Results Radium-226 Cores from the groundwater-augmented lake s all display upco re increases in 226Ra activity (Figure 4-2). Surface sediments (0-4 cm) possess about an order of magnitude more 226Ra activity than do deeper sediment s. Topmost samples range in 226Ra activity from 7.6 dpm g-1 in Little Hobbs Lake to 44.9 dpm g-1 in Lake Charles. Surface sediments exceed 5 dpm g-1, a value suggested by Brenner et al. (2004) as indicative of anthropogenic 226Ra enrichment. Stratigraphic distribution of 226Ra in the cores indicates that enrichment occurred recently. Several depths in the Lake Charles core possess 226Ra activities >30 dpm g-1 and are the highest values yet reported for a Florida lake sedi ment core. Radium-226 activity in the Lake

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30 Charles core varies from 7.2 dpm g-1 in the 88-92 cm sample to 44.9 dpm g-1 in the topmost sample (0-4 cm). Lead-210 Total 210Pb activity in the Lake Charles core ranges from 8.7 to 39.2 dpm g-1, with higher values recorded in the upper portion of the core (Figure 4-2 A). Isotopic disequilibrium (226Ra/210Pb) is apparent at depths in the Charles, Saddleback, and Crystal cores where 226Ra activity exceeds total 210Pb activity (Figure 4-2 A, B, D). This suggests the lakes r eceived dissolved 226Ra that separated from its parent isotopes (e.g., 238U) and did not yet equilibrate with its daughters (e.g., 210Pb). Disequilibrium is most obvious in shallow deposits of the Charles and Saddleback cores where 226Ra is greater than total 210Pb. In these recent sediments, 226Ra activity exceeds the combined act ivities of supported and unsupported (excess) 210Pb, indicating the presence of significant 226Ra without its daughters. Geochemical Results Organic matter The organic matter concentration in the Lake Charles sediment core ranges from 25.8% to 43.3%. Organic content is inversel y correlated with depth in the sediment core (r = -0.58, n = 24, P<0.01) (Figure 4-3 A). The organic matter concentra tions in Lakes Saddleback, Cr ystal, and Little Hobbs sediment cores range from 29.4% to 66.4%, 0% to 45.9%, and 2.76% to 59.3%, respectively (Appendix A). Calcium The calcium concentrations in all four lake sediment cores were generally greater in the upper half of the cores (Figure 4-3 B). Calcium c oncentration in the Lake Charles sediment core ranges from 0.54 mg g-1 to 10.06 mg g-1 (Appendix A). Calcium c oncentration in the Lake

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31 Saddleback sediment core ranges from 0.25 mg g-1 to 190.3 mg g-1, and sharply decreases below the 16 cm sample (84.6 mg g-1) (Appendix A). Lake Crystals ca lcium concentration exhibits a narrow range, from 0.0 mg g-1 to 0.59 mg g-1 (Appendix A). Calcium concentration in Little Hobbs Lake ranges from 0.0 mg g-1 to 2.3 mg g-1 (Appendix A). Total phosphorus Total P concentration in the Lake Ch arles core varies from 0.51 mg g-1 in the 20-24 cm sample to 0.82 mg g-1 in the surface sediment sample (0 4 cm) (Figure 4-3 C). The sediment core from Lake Saddleback has a Total P concentration rangi ng from 0.33 mg g-1 to 0.67 mg g-1 (Appendix A). Total P concentration in the Lake Crystal core varies from 0.03 mg g-1 to 1.12 mg g-1 (Appendix A). Total P concentration in Little Hobbs Lake ranges from 0.05 mg g-1 to 1.91 mg g-1 (Appendix A). Ra-226 vs. Geochemical Results Radium-226 stratigraphy in each core was co mpared with the stratigraphic distribution of other geochemical variables (organic matter [O M], calcium [Ca], magn esium [Mg], and total phosphorus [P]) to explore the mode of radium deliv ery to the lakes. Prev ious studies of Florida lakes showed a strong correlation between sediment total P and 226Ra, suggesting both were delivered by a common mechanism. It was prop osed that colluvial or aeolian processes had delivered phosphate-rich, Ra-containing particle s to the lakes (Brenner et al. 1994, 1997). Study of groundwater-augmented Round Lake, however showed a strong correlation between 226Ra activity and both inorganic (carbona te) carbon and Ca in sediment cores. This suggested that bicarbonate-rich groundwa ter was the source of 226Ra entering Round Lake (Brenner et al. 2000). High levels of 226Ra in Round Lake biota also pointed to a dissolved source of the radionuclide. Sediment cores from Lakes Charles, Saddleb ack, Little Hobbs, and Crystal show a strong stratigraphic correlation between 226Ra and Ca concentrations (Tab le 4-1, Figure 4-4 A). Among

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32 lakes, the correlation is weakest in Lake Char les (r = 0.82), but is nonetheless strong (p<0.001). The Lake Charles core does not disp lay a significant correlation between 226Ra and total P over its entire length, but 226Ra and total P are highly correlated in the top 52 cm (r = 0.68, p<0.01), where 226Ra activity increases abrupt ly. Radium-226 activity and OM content are positively correlated throughout the Charles core and this correlation is stronger (r = 0.89, p<0.001) when only the topmost sediments (0-52 cm ) are considered (Figure 4-4 B). In the Crystal Lake core, the only vari able significantly correlated with 226Ra activity was Ca (r = 0.94, p<0.001) (Table 4-1). In the Little Hobbs core, Ca, Mg, P, and OM were positively correlated with 226Ra at p<0.01 or p<0.001 (Table 4-1). Th e Saddleback core displays a very strong positive correlation between Ca and 226Ra (r = 0.99, p<0.001), as well as between Mg and 226Ra (r = 0.95, p<0.001) (Table 41). The correlation between 226Ra and P is weaker, but significant (r = 0.69, p<0.05). Radium-226 activity in the Saddleback core shows a strong negative correlation with organic matter. St rontium was measurable in the Charles and Saddleback sediments. In the Saddleback deposits Sr concentrations we re highest in nearsurface sediments and highly correlated with 226Ra (r = 0.98, p<0.001). In the Lake Charles core, highest Sr concentrations were associated with recent sediments, with the exception of a single peak at 104-108 cm. Excluding this sample, Sr concentrations and 226Ra activities are strongly correlated (r = 0.68, p<0.001). Radium-226 activity is positively correlated with OM content in the core (r = 0.57, n = 24, P<0.1). Radium-226 activity is also positively co rrelated with calcium concentration in the sediment core (r = 0.80, n = 24, p<0.001), but is not significantly correlated with TP concentration.

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33 Dating Sediment Cores Attempts to date the cores using gamma coun ting proved problematic. None of the cores showed a distinct 137Cs peak (Figure 4-2). The 1963 bomb fallout peak is commonly blurred in Florida lake sediments that la ck 2:1 layer clays and bind cesiu m poorly (Brenner et al. 2004). Soluble 137Cs is prone to transport within sedime nts and probably moves downward through the sediment lens in these hydrologically leaky lakes. High and variable 226Ra activities in the cores from Lakes Charles, Saddleback, Little Hobbs, and Crystal create difficulties for 210Pb dating. Disequilibrium between 226Ra and supported 210Pb makes it impossible to estimate unsupported 210Pb activity accurately and confounds da ting (Brenner et al. 2004). The large amount of dissolved 226Ra introduced into the lakes will equilibrate with (supported) 210Pb only after ~110 years, i.e., about 5 half-lives (22.3 yr) of 210Pb. Deeper sediments in the cores, where 226Ra and 210Pb activities are low and similar, are proba bly >100 years old, as they apparently possess no unsupported 210Pb. Another line of evidence that these are recent deposits is that there is no 137Cs at great depth in the cores. In all four cores, it appe ars that more than a century of accumulated sediment was retrieved (Figure 4-2). Table 4-1. Correlation coefficients (r) of stratigraphic correlation between 226Ra activity and concentrations of calcium (Ca), magnes ium (Mg), total phosphorus (P), strontium (Sr), and organic matter (OM) in sediment cores from Lake Charles, Saddleback, Little Hobbs, and Crystal. Lake Name Ca Mg P Sr OM (%LOI) Charles (226Ra) 0.82*** 0.03ns 0.03ns 0.68*** 0.61*** Saddleback (226Ra) 0.99*** 0.95*** 0.69* 0.98*** -0.96*** Little Hobbs (226Ra) 0.94*** 0.68*** 0.89***NM 0.56** Crystal (226Ra) 0.94*** 0.44ns 0.03ns NM -0.08ns Note: *p<0.05, **p<0.01, ***p<0.001, ns = not significan t (p>0.05), n values for Charles = 29 (Ca, Mg) and 26 (P, OM), Crystal = 12, L ittle Hobbs = 22, Saddleback = 10, NM = Not Measurable

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34 Figure 4-1. Scatter plot show ing the relation between orga nic matter concentration and 226Ra activity in surface sediments fr om Lake Charles (r = 0.77).

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35 Figure 4-3. Radionuclide (226Ra, 210Pb, 137Cs) activities (in dpm g-1) in sediment cores from groundwater augmented study lakes. A) Lake Charles. B) Lake Saddleback. C) Little Hobbs Lake. D) Crystal Lake. A

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36 Figure 4-3. Continued B

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37 Figure 4-3. Continued C

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38 Figure 4-3. Continued D

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39 Figure 4-4. Concentrations in the Lake Charle s sediment core of: A) Organic matter versus depth. B) Total phosphorus versus depth. C) Calcium concentration versus depth. A

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40 Figure 4-4. Continued B

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41 Figure 4-4. Continued C

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42 50 45 40 35 30 25 20 0 10 20 30 40 50 Lake Charles Core Organic matter (% LOI)Ra-226 (dpm/g)y = 1.600x 33.03, R2 = 0.329a. 12 10 8 6 4 2 0 0 10 20 30 40 50 Lake Charles Core Calcium (mg/g)Ra-226 (dpm/g)y = 3.368x + 11.543, R2 = 0.647b. Figure 4-5. Scatter plots show ing the relation between: A) Organic matter concentration and 226Ra activity in the Lake Charles sediment core (r = 0.57). B) Calcium concentration and 226Ra activity in the Lake Char les sediment core (r = 0.80). A B

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43 CHAPTER 5 DISCUSSION Lake Charles Surface Sediments Surface sediment samples from Lake Charle s represent material deposited recently, probably since the initiation of hydrologic augmentation. Radium-226 in these topmost deposits is associated primarily with organic matter. Sediments in most Flor ida lakes are composed principally of quartz sands and organic matter, bu t possess little inorgani c silt and clay. A study of surface sediments from 34 Florida lakes demons trated that both calcium and magnesium were positively correlated with OM content (Bre nner and Binford 1986). Radium-226, another divalent cation, evidently behaves in a similar fa shion, adsorbing to the OM fraction in the Lake Charles surface sediments. Higher 226Ra activities in sediments from deeper-water sites in Lake Charles may reflect the high concentration of fi ne organic particles at these deep locations. Study Lake Sediment Cores High 226Ra activities (>40 dpm g-1) near the top of the Lake Charles core indicate substantial delivery of the radi onuclide during the lakes 35 y ears of hydrologic augmentation. The activity measured in the topmost sample (44.9 dpm g-1) is the highest yet measured in a Florida lake. Radium-226 activities exceed total 210Pb activities at several depths in the core, indicating there is disequilibrium between the tw o radionuclides. Lake Charles is one of only three Florida lakes in which radioisotopic disequilibrium has been demonstrated definitively (Brenner et al. 2004). Calcium concentration is relatively low (<2.0 mg g-1) below 44 cm depth in the Lake Charles core, but increases above that depth. The higher calcium concentrations in uppermost sediments reflect the recent deli very of Ca in bicarbonate-rich gr oundwater. Up-core increase in Ca concentration was also documented in nearby Round Lake, which has been augmented with

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44 Floridan Aquifer water since 1966 (Brenner et al. 2000). Strong stra tigraphic correlation between Ca concentration and 226Ra activity (r = 0.80) suggests that both ions are delivered via the same process, namely groundwater input. Though Ca concentration and 226Ra activity correlate, some radium may make its way to the sediment bound in carbonate. High amounts of 226Ra were shown to have been incorporated in to the calcium carbonate shells of snails and mussels that inhabit augmented lakes (Brenner et al. 2000, 2007). There is no significant correlation between TP and 226Ra in the Lake Charles sediment core, contrary to findings in several Florida lakes. In 12 cores from eight other Florida lakes, TP and 226Ra showed strong stra tigraphic correlation (Bre nner et al. 1997). It wa s suggested that the two elements were delivered to the lakes with erosional or aeolian particulate material. Groundwater entering Lake Charles has a 226Ra activity of ~3 dpm L-1, well below the drinking water standard. The di ssolved radionuclide adsorbs to organic matter particles that accumulate on the lake bottom. Consequently, 226Ra activity in recent sediments can be high. Previous investigations show that input of dissolved 226Ra to lakes has biological implications. For instance, bivalves from Round Lake we re shown to accumulate high levels of 226Ra in their tissues (Brenner et al. 2 000). A mussel sample ( Elliptio buckleyi ) from Lake Charles yielded the highest 226Ra activity yet measured from pelecypods in a Florida lake (619 dpm g-1) (Brenner et al. 2007). Other infaunal organisms, such as ch ironomid larvae and oligochaetes, may also be exposed to high 226Ra activities in surface de posits and may bioaccumulate the radionuclide. Sediment cores from Lakes Charles, Saddleback Little Hobbs, and Crystal all show recent enrichment with 226Ra. Radium-226 activities in surf ace sediments are about an order of magnitude greater than baseline ac tivities in the deepest levels of the cores. Topmost (0-4 cm) samples in all four cores had 226Ra activities >5 dpm g-1, and Lakes Saddleback and Charles

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45 displayed values of 17.5 and 44.9 dpm g-1, respectively. The 226Ra values are much greater than those measured in lakes and wetlands that receiv e most of their hydrolog ic input from surface waters (Brenner et al. 1999, 2001, 2004). High activities were meas ured previously in surface deposits of groundwater-augmented Round Lake (26.9 and 26.8 dpm g-1) (Brenner et al. 2000), and in topmost sediments from Lake Rowell (18.4 dpm g-1). Although Lake Rowell is not deliberately augmented, it is now suspected that it, too, may receive substantial 226Ra in groundwater inputs from water pumped for mining and domestic use. Pumped Floridan Aquifer water is probably the source of much 226Ra activity in sediment cores from the study lakes. Several lines of ev idence implicate augmentation water. First, the 210Pb and 226Ra stratigraphies show the increase in 226Ra occurred recently, probably within the last few decades. Second, deep groundw aters in the region contain appreciable 226Ra. Augmentation water entering the stu dy lakes ranges from 0.82 dpm l-1 (Little Hobbs) to 3.26 dpm l-1 (Saddleback). Third, there is 226Ra/210Pb disequilibrium at depths in the Charles, Crystal, and Saddleback cores. This suggests that 226Ra enters the lakes in dissolved form, separated from its precursors and not yet equilibrated with its daughters. Fourth, all four cores show a strong stratigraphic correlation between 226Ra and Ca, and both elements are recent additions to the sediment. Groundwater is rich in calcium bicarbonate a nd was added to the lakes in substantial quantity only with th e onset of augmentation. Fifth, gr eater Sr in the recent deposits of Charles and Saddleback lakes also indicates groundwater input. Strontium concentrations in limestone are high compared to concentrations in the surficial quartz sands that surround the lakes. Although augmentation wa ter is the probable source of 226Ra that reaches the lake sediments, recent increases in 226Ra have also been detected in cores from Florida lakes that do not receive deliberate augmentation (Brenner et al. 2004). Groundwater input may also be the

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46 source for 226Ra in these lakes, but may be pumped to the surface for other reasons, including crop irrigation, residential, mining, and industrial uses, after which it runs off into local water bodies. In most Florida lake sediment core s that display an upcore increase in 226Ra activity, the change is rather continuous over the uppermost de posits, reaching highest ac tivities in surface or near-surface layers. There are se veral possible explanations for th is smooth trend. First, since the onset of groundwater input, there may have been a steady increase in the amount of groundwater reaching the lakes. This may be true for Florida lakes with watersheds that have been subject to increasing development over th e last century, such as those in Hillsborough County, but it is an unlikely explan ation for this trend in groundw ater-augmented systems. The latter group of lakes has receiv ed groundwater supplements at varying rates over the years, depending on rainfall amount and the n eed for augmentation. The pattern of 226Ra distribution in the sediments of groundwater-augmented lakes ma y reflect, in part, downward transport and adsorption of dissolved 226Ra on the sediment lens, with most 226Ra adhering to near-surface deposits. Florida lakes can lose a substantia l amount of water to dow nward leakage (Deevey 1988) and augmented lakes are especially leaky (Metz and Sacks 2002), hence their need for groundwater supplements. This downward transport of 226Ra may also explai n why the initial rise of 226Ra activity in cores may appear in se diments deposited prior to the onset of groundwater augmentation. Sediment cores from Lakes Charles, Saddl eback, Little Hobbs, and Crystal display geochemical changes in their uppermost deposits. Cores from all four lakes show upcore increases in 226Ra activity, Ca, and Mg c ontent. The Charles and Saddleback cores display a general increase in Sr concentr ation. The recent geochemical and biological changes in the

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47 sediment records are consistent with shifts that might be expected as a consequence of deliberate groundwater augmentation. Inadvertent addition of deep groundwater associated with past agriculture and residential devel opment in the watershed also might have contributed to changes that are evident in the sediment record.

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48 APPENDIX DATA Appendix A-1. Data from Lake Charles Sediment Samples. Water Depth (m) TYPE Ra-226 Activity (dpm g-1) Ra-226 Activity %OM 0.00 Transect 1 7.51.4 14.3 0.31 Transect 1 2.90.5 9.1 0.91 Transect 1 10.72.0 38.4 1.83 Transect 1 8.90.9 25.6 0.00 Transect 2 0.60.8 0.0 0.31 Transect 2 0.60.4 1.3 0.91 Transect 2 10.51.2 28.9 1.83 Transect 2 15.81.2 16.8 0.00 Transect 3 4.60.6 19.0 0.31 Transect 3 1.50.7 6.9 0.91 Transect 3 2.30.3 4.7 1.83 Transect 3 10.60.9 16.8 0.00 Transect 4 3.00.1 6.4 0.31 Transect 4 3.50.5 0.0 0.91 Transect 4 12.30.9 25.7 1.83 Transect 4 7.81.4 9.4 0.00 Transect 5 2.80.2 4.6 0.31 Transect 5 3.00.2 3.5 0.91 Transect 5 8.10.3 19.8 1.83 Transect 5 8.53.4 25.5 2.40 Deep Surface Grab 11.32.1 21.4 4.70 Deep Surface Grab 14.70.9 15.5 2.60 Deep Surface Grab 12.911.7 28.6 3.00 Deep Surface Grab 8.82.5 11.0 1.20 Deep Surface Grab 12.81.6 27.1 2.00 Deep Surface Grab 16.51.0 22.3 1.30 Deep Surface Grab 11.30.2 24.3 1.85 Deep Surface Grab 11.90.7 25.2 2.55 Deep Surface Grab 15.60.6 23.8 2.50 Deep Surface Grab 23.90.9 32.1 Note: m = meters, dpm g-1 = decays per minute per gram, = standard deviation, %OM = percent organic matter, Ra-226 Co rrected Mean Activity and Correct ed Standard Deviations are given.

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49 Appendix A-2. Data from sediment cores taken in Lakes Charles, Crystal, Little Hobbs, and Saddleback. Lake Sample Depth (cm) Corrected Mean Ra-226 Activity (dpm g-1) Corrected Ra-226 Activity Pb-210 (dpm g-1) Pb-210 Error Cs-137 (dpm g-1) Cs-137 Error Charles 4 44.9 3.1 34.2 0.9 1.1 0.1 Charles 8 42.6 2.1 35.4 0.9 1.0 0.1 Charles 12 42.1 2.9 39.2 0.8 1.0 0.1 Charles 16 39.1 2.2 34.0 0.9 0.9 0.1 Charles 20 37.1 3.9 38.3 0.9 1.3 0.1 Charles 24 22.1 0.4 18.0 0.5 1.3 0.1 Charles 28 29.7 1.7 28.0 0.6 2.5 0.1 Charles 32 34.9 2.4 32.1 0.7 2.6 0.1 Charles 36 31.3 2.2 28.2 0.4 2.7 0.1 Charles 40 30.2 1.6 22.7 0.5 3.2 0.1 Charles 44 31.2 1.4 25.4 0.8 4.0 0.2 Charles 48 29.7 1.2 21.5 0.6 3.9 0.1 Charles 52 25.2 1.2 17.5 0.5 4.4 0.1 Charles 56 17.2 2.0 15.9 0.5 3.9 0.1 Charles 60 17.9 0.4 14.0 0.4 5.6 0.1 Charles 64 13.8 0.4 11.9 0.3 7.1 0.1 Charles 68 11.6 0.9 12.5 0.5 7.3 0.2 Charles 72 11.4 0.2 13.6 0.4 8.1 0.2 Charles 76 10.9 0.3 12.5 0.4 8.2 0.2 Charles 80 10.5 1.0 15.4 0.4 9.0 0.2 Charles 84 9.6 0.6 13.1 0.4 9.1 0.2 Charles 88 7.9 0.6 11.9 0.2 9.5 0.1 Charles 92 7.2 0.2 8.7 0.3 9.6 0.2 Charles 96 7.3 0.4 9.5 0.2 9.1 0.1 Charles 100 6.7 0.2 10.3 0.3 6.7 0.1 Charles 104 6.6 0.3 8.8 0.3 5.1 0.1 Charles 108 10.0 0.2 10.6 0.3 5.0 0.1 Charles 112 5.1 0.4 1.4 0.1 1.6 0.0 Charles 114 3.7 0.2 2.2 0.1 1.1 0.1

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50 Appendix A-2. Continued Lake Sample Depth (cm) %OM Calcium Concentration (mg/g) Magnesium Concentration (mg/g) Strontium Concentration (mg/g) Total Phosphorus (mg/g) Charles 4 42.7 4.4 0.5 0.0 0.8 Charles 8 42.3 7.1 0.5 0.0 0.7 Charles 12 43.3 7.4 0.6 0.0 0.8 Charles 16 40.8 10.1 0.5 0.0 0.6 Charles 20 42.3 10.1 0.5 0.0 0.7 Charles 24 33.2 5.0 0.3 0.0 0.5 Charles 28 36.9 5.1 0.5 0.0 0.8 Charles 32 36.0 5.7 0.5 0.0 0.6 Charles 36 33.8 7.6 0.5 0.0 0.6 Charles 40 32.9 4.6 0.5 0.0 0.6 Charles 44 32.5 2.9 0.5 0.0 0.6 Charles 48 31.9 1.8 0.5 0.0 0.6 Charles 52 30.6 1.3 0.4 0.0 0.6 Charles 56 25.8 0.5 0.3 0.0 0.6 Charles 60 32.9 1.0 0.4 0.0 0.7 Charles 64 35.3 1.4 0.5 0.0 0.8 Charles 68 35.0 1.4 0.5 0.0 0.8 Charles 72 36.1 1.3 0.6 0.0 0.8 Charles 76 38.0 1.3 0.6 0.0 0.8 Charles 80 37.0 1.2 0.6 0.0 0.8 Charles 84 36.9 1.2 0.6 0.0 0.8 Charles 88 32.8 1.0 0.6 0.0 0.8 Charles 92 30.9 1.0 0.6 0.0 0.8 Charles 96 29.0 0.5 0.5 0.0 0.7 Charles 100 0.0 0.5 0.5 0.0 0.7 Charles 104 24.2 0.3 0.4 0.0 Charles 108 0.0 3.7 0.7 0.0 Charles 112 11.7 0.4 0.4 0.0 0.3 Charles 114 0.0 0.2 0.3 0.0

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51 Appendix A-2. Continued Lake Sample Depth (cm) Corrected Mean Ra-226 Activity (dpm g-1) Corrected Ra-226 Activity Pb-210 (dpm g-1) Pb-210 Error Cs-137 (dpm g-1) Cs-137 Error Crystal 4 8.5 0.6 16.1 0.3 3.2 0.1 Crystal 8 6.8 0.4 16.6 0.4 3.7 0.1 Crystal 12 6.7 0.7 14.6 0.4 4.0 0.1 Crystal 16 4.6 0.3 10.3 0.3 2.1 0.1 Crystal 20 2.9 0.1 1.9 0.1 0.8 0.0 Crystal 24 2.0 0.3 2.3 0.2 0.7 0.0 Crystal 28 1.9 0.3 1.2 0.1 0.4 0.0 Crystal 32 1.7 0.1 -0.5 0.0 0.3 0.0 Crystal 36 1.7 0.3 1.7 0.1 0.2 0.0 Crystal 40 1.2 0.1 0.5 0.1 0.1 0.0 Crystal 44 1.3 0.2 1.6 0.1 0.0 0.0 Crystal 48 1.8 0.1 1.5 0.1 0.0 0.0

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52 Appendix A-2. Continued Lake Sample Depth (cm) %OM Calcium Concentration (mg/g) Magnesium Concentration (mg/g) Strontium Concentration (mg/g) Total Phosphorus (mg/g) Crystal 4 26.9 0.6 0.6 0.0 0.7 Crystal 8 26.0 0.4 0.6 0.0 0.7 Crystal 12 29.4 0.6 0.7 0.0 0.8 Crystal 16 38.8 0.4 0.7 0.0 1.0 Crystal 20 41.3 0.3 0.6 0.0 1.0 Crystal 24 45.9 0.2 0.7 0.0 1.1 Crystal 28 45.6 0.2 0.7 0.0 1.0 Crystal 32 34.7 0.1 0.6 0.0 0.7 Crystal 36 24.9 0.1 0.5 0.0 0.6 Crystal 40 24.9 0.0 0.5 0.0 0.7 Crystal 44 18.9 0.0 0.4 0.0 0.5 Crystal 48 19.8 0.0 0.4 0.0 0.6 Crystal 52 32.5 0.0 0.5 0.0 0.5 Crystal 56 34.5 0.0 0.5 0.0 0.5 Crystal 60 35.6 0.0 0.5 0.0 0.5 Crystal 64 20.4 0.0 0.4 0.0 0.5 Crystal 68 9.2 0.0 0.2 0.0 0.3 Crystal 72 7.9 0.0 0.1 0.0 0.3 Crystal 76 5.0 0.0 0.1 0.0 0.2 Crystal 80 3.6 0.0 0.1 0.0 0.1 Crystal 84 3.0 0.0 0.1 0.0 0.1 Crystal 88 2.9 0.0 0.1 0.0 0.0 Crystal 92 8.1 0.0 0.2 0.0 0.2 Crystal 96 0.0 0.0 0.6 0.0 0.2 Crystal 100 0.0 0.0 0.4 0.0 0.2 Crystal 104 0.0 0.0 0.3 0.0 0.1 Crystal 106 0.0 0.0 0.4 0.0 0.2

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53 Appendix A-2. Continued Lake Sample Depth (cm) Corrected Mean Ra-226 Activity (dpm g-1) Corrected Ra-226 Activity Pb-210 (dpm g-1) Pb-210 Error Cs-137 (dpm g-1) Cs-137 Error Little Hobbs 4 7.6 0.3 25.9 0.4 3.0 0.1 Little Hobbs 8 7.5 0.4 26.0 0.3 3.4 0.1 Little Hobbs 12 7.8 0.4 24.4 0.4 3.5 0.1 Little Hobbs 16 8.0 0.1 20.7 0.5 4.3 0.1 Little Hobbs 20 8.5 0.9 21.1 0.5 4.7 0.1 Little Hobbs 24 7.7 0.4 18.5 0.3 4.9 0.1 Little Hobbs 28 6.7 0.6 16.7 0.4 4.4 0.1 Little Hobbs 32 6.7 0.7 13.5 0.4 2.2 0.1 Little Hobbs 36 6.4 0.9 13.3 0.4 1.9 0.1 Little Hobbs 40 5.3 0.6 13.3 0.5 1.0 0.1 Little Hobbs 44 4.9 0.1 11.0 0.3 1.3 0.0 Little Hobbs 48 4.5 0.2 10.0 0.4 1.4 0.1 Little Hobbs 52 3.5 0.2 11.0 0.3 1.0 0.0 Little Hobbs 56 3.2 0.1 9.1 0.2 0.7 0.0 Little Hobbs 60 2.5 0.3 6.3 0.2 0.6 0.0 Little Hobbs 64 2.1 0.4 4.2 0.2 0.5 0.0 Little Hobbs 68 1.2 0.3 4.3 0.2 0.4 0.0 Little Hobbs 72 1.2 0.3 0.3 0.1 0.2 0.0 Little Hobbs 76 0.4 0.0 0.4 0.0 0.1 0.0 Little Hobbs 80 0.4 0.0 1.0 0.1 0.0 0.0 Little Hobbs 84 0.5 0.2 0.4 0.0 0.0 0.0 Little Hobbs 88 0.3 0.2 -0.3 0.0 0.0 0.0

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54 Appendix A-2. Continued Lake Sample Depth (cm) %OM Calcium Concentration (mg/g) Magnesium Concentration (mg/g) Sr Concentration (mg/g) Total Phosphorus (mg/g) Little Hobbs 4 38.1 2.0 0.7 0.0 1.6 Little Hobbs 8 38.7 2.1 0.7 0.0 1.7 Little Hobbs 12 38.8 2.2 0.7 0.0 1.8 Little Hobbs 16 38.8 2.3 0.8 0.0 1.9 Little Hobbs 20 38.3 2.0 0.7 0.0 1.8 Little Hobbs 24 36.9 2.0 0.7 0.0 1.9 Little Hobbs 28 34.4 1.7 0.7 0.0 1.7 Little Hobbs 32 43.5 1.5 0.7 0.0 1.9 Little Hobbs 36 52.9 1.0 0.8 0.0 1.9 Little Hobbs 40 56.4 0.8 0.8 0.0 1.9 Little Hobbs 44 58.5 0.6 0.9 0.0 1.9 Little Hobbs 48 59.3 0.4 0.9 0.0 1.8 Little Hobbs 52 58.9 0.3 0.9 0.0 1.5 Little Hobbs 56 57.7 0.2 0.9 0.0 1.4 Little Hobbs 60 48.0 0.1 0.8 0.0 1.1 Little Hobbs 64 37.3 0.1 0.7 0.0 0.8 Little Hobbs 68 26.8 0.0 0.5 0.0 0.8 Little Hobbs 72 20.4 0.0 0.4 0.0 0.7 Little Hobbs 76 5.0 0.0 0.2 0.0 0.1 Little Hobbs 80 4.0 0.0 0.1 0.0 0.1 Little Hobbs 84 3.2 0.0 0.1 0.0 0.0 Little Hobbs 88 3.3 0.0 0.1 0.0 0.1 Little Hobbs 92 2.8 0.0 0.1 0.0 0.0 Little Hobbs 96 3.0 0.0 0.1 0.0 0.1

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55 Appendix A-2. Continued Lake Sample Depth (cm) Corrected Mean Ra-226 Activity (dpm g-1) Corrected Ra-226 Activity Pb-210 (dpm g-1) Pb-210 Error Cs-137 (dpm g-1) Cs-137 Error Saddleback 4 17.5 1. 7 19.1 0.6 1.7 0.1 Saddleback 8 15.3 1. 2 18.5 0.6 1.7 0.1 Saddleback 12 12.8 0. 9 10.2 0.3 2.2 0.1 Saddleback 16 9.2 1. 3 7.5 0.4 2.6 0.1 Saddleback 20 3.1 0. 1 4.2 0.2 1.8 0.1 Saddleback 24 2.6 0. 2 1.8 0.2 1.7 0.1 Saddleback 28 2.3 0. 4 1.4 0.2 1.2 0.1 Saddleback 32 1.9 0. 3 1.3 0.1 1.0 0.1 Saddleback 36 1.6 0. 4 1.8 0.1 1.0 0.0 Saddleback 40 2.2 0. 2 0.8 0.1 0.8 0.0

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56 Appendix A-2. Continued Lake Sample Depth (cm) %OM Calcium Concentration (mg/g) Magnesium Concentration (mg/g) Strontium Concentration (mg/g) Total Phosphorus (mg/g) Saddleback 4 31.0 190.3 0.8 0.1 0.6 Saddleback 8 29.4 186.7 0.8 0.1 0.5 Saddleback 12 30.5 170.6 0.8 0.1 0.4 Saddleback 16 39.0 84.6 0.6 0.1 0.4 Saddleback 20 53.9 5.2 0.4 0.0 0.5 Saddleback 24 60.8 4.8 0.5 0.0 0.4 Saddleback 28 61.0 4.8 0.5 0.0 0.4 Saddleback 32 59.2 3.9 0.5 0.0 0.4 Saddleback 36 57.8 2.1 0.5 0.0 0.4 Saddleback 40 54.0 1.8 0.5 0.0 0.3 Saddleback 44 59.2 1.2 0.6 0.0 0.4 Saddleback 48 62.4 1.1 0.6 0.0 0.4 Saddleback 52 65.6 1.1 0.6 0.0 0.4 Saddleback 56 65.6 1.1 0.6 0.0 0.5 Saddleback 60 66.4 0.9 0.6 0.0 0.5 Saddleback 64 66.2 0.9 0.6 0.0 0.5 Saddleback 68 0.0 0.9 0.6 0.0 0.5 Saddleback 72 66.0 0.7 0.6 0.0 0.6 Saddleback 76 62.7 0.7 0.6 0.0 0.6 Saddleback 80 61.0 0.5 0.6 0.0 0.7 Saddleback 84 59.1 0.5 0.6 0.0 0.7 Saddleback 88 53.4 0.4 0.6 0.0 0.6 Saddleback 92 49.7 0.3 0.6 0.0 0.6 Saddleback 96 47.1 0.3 0.6 0.0 0.6 Saddleback 100 43.7 0.3 0.6 0.0 0.6 Note: cm = centimeters, dpm g-1 = decays per minute per gram, = standard deviation, Ra-226 = Radium-226, Pb-210 = Lead-210, Cs-137 = Ce sium-137, %OM = Percent organic matter, mg/g = milligrams per gram, nd = non detected

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57 LIST OF REFERENCES Andersen JM (1976) An ignition method for determination of total phosphorus in lake sediments. Water Res 10: 329-331. Brenner M, Binford MW (1986) Ma terial transfer from water to sediment in Florida lakes. Hydrobiologia 143: 55-61. Brenner M, Peplow AJ, Schelske CL (1994) Disequilibrium between Ra-226 and supported Pb210 in a sediment core from a shallow Florida lake. Limnol Oceanogr 39: 1222-1227. Brenner M, Schelske CL, Kenney WF (2004) Inputs of dissolved and particulate Ra-226 to lakes and implications for Pb-210 dating recent sediments. J Paleolimnol 32: 53-66. Brenner M, Schelske CL, Whitmore TJ (1997) Radium-226 stratigraphy in Florida lake sediments as an indicator of human disturba nce. Verh Internat Verein Limnol 26: 809-813. Brenner M, Smoak JS, Allen MS, Schelske CL Leeper DA (2000) Biol ogical accumulation of 226 Ra in a groundwater-augmented Florid a lake. Limnol Oceanogr 45: 710-715. Brenner M, Smoak JM, Leeper DA, Streubert M, Baker SM (2007) Radium-226 accumulation in Florida freshwater mussels. Limnol Oceanogr 52: 1614-1623. Brenner M, Whitmore TJ (1999) Paleolimnological reconstruction of water quality for Lakes Dosson, Halfmoon, and Round in Hillsborough C ounty, Florida. Final Report to the Southwest Florida Water Manageme nt District, Br ooksville, FL. Deevey ES (1988) Estimation of downward leak age from Florida lakes. Limnol Oceanogr 33:1308. Dooris PM, Dooris GM, Martin DF (1982) Phyt oplankton responses to ground water addition in central Florida lakes. Water Res Bull 18:335. Dooris PM, Martin DF (1979) Ground-water indu ced changes in lake chemistry. Ground Water 17:324. Fanning KA, Breland JA II, Byrne RH (1982) Ra dium-226 and radon-222 in the coastal waters of west Florida: high concentrations and atmospheric degassing. Science 215:667. Fisher MM, Brenner M, Reddy KR (1992) A simple, inexpensive piston corer for collecting undisturbed sediment/water interface profiles. J Paleolimnol 7: 157-161. Hkanson L, Jansson M (1983) Principles of lake sedimentology. Sp ringer-Verlag, New York, 316 p.

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58 Harada K, Burnett WC, Larock PA, Cowart JB (1989) Polonium in Florida groundwater and its possible relationship to the sulfur cycle and bacteria. Geochim Cosmochim Acta 53:143 150. Hazardous Substance and Waste Management Research, Inc. (2000) Human health risk assessment and preliminary ecological evaluati on regarding potential exposure to Radium226 in several central Florida lakes ecosyste ms. Report to the Southwest Florida Water Management District, Brooksville, FL, 21 pp. + appendices Hazardous Substance and Waste Management Research, Inc. (2004) Human health risk assessment regarding potential exposure to Radium-226 in two central Florida lake systems. Report to the Southwest Florida Wa ter Management District, Brooksville, FL, 15 pp. + appendices Kaufmann RF, Bliss JD (1977) Effects of phospha te mineralization and the phosphate industry on radium-226 in ground water of central Flor ida. US Environmental Protection Agency Final Report EPA/520-6-77-010. EPA Office of Radiation Programs, Las Vegas, NV Krishnaswami S, Lal D (1978) Radionuclide lim nochronology. In: Lerman A (ed) Lakes: chemistry, geology, physics. Springer-Verlag, New York, pp 153 Martin DF, Victor DM, Dooris PM (1976a) Effect s of artificially intr oduced ground water on the chemical and biochemical characteristics of six Hillsborough County (Florida) lakes. Water Res 10:65 Martin DF, Victor DM, Dooris PM (1976b) Imp lications of lake augmentation on growth of Hydrilla. J Environ Sci Health 3:245 Metz PA, Sacks LA (2002) Comparison of the hydrogeology and water quality of a groundwater augmented lake with two non-augmented lakes in northwest Hillsborough County, Florida. US Geological Survey Water Resources Investigation Report 02-4032. Tallahassee, FL, 74 pp Miller RL, Kraemer TF, McPher son BF (1990) Radium and radon in Charlotte Harbor Estuary, Florida. Estuarine, Coastal Shelf Sci 31:439 Moore WS (1984) Radium isotope measurements using germanium detectors. Nucl. Inst. Methods 223: 407-411. Schelske CL, Conley DJ, Stoermer EF, Newbe rry TL, Campbell CD (1986) Biogenic silica and phosphorus accumulation in sediments as indices of eutrophication in the Laurentian Great Lakes. Hydrobiologia 143: 79-86. Schelske CL, Peplow AJ, Brenner M, Spen cer CN (1994) Low-background gamma counting: applications for 210 Pb dating of sediments. J Paleolimnol 10: 115-128.

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59 Scott TM (1997) Miocene to Holocene history of Florida. In: Randazzo, AF & Jones, DS (eds.): The geology of Florida: pp 57-67. Univer sity Press of Florida, Gainesville. Stewart JW, Hughes GH (1974) Hydrologic conse quences of using ground water to maintain lake levels affected by water wells near Tampa, Florida. USGS Survey Report of Investigations No 74. Florida DNR, Tallahassee. Smoak JM, Krest JM (2006) Source of radium in a well-water-augmented Florida Lake. J. Environmental Radioactivity. 89:102-114. Upchurch SB, Randazzo AF (1997) Environmenta l geology of Florida. In: Randazzo AF, Jones DS (eds) The geology of Florida: pp 217. Univer sity Press of Florida, Gainesville FL. United States Census Bureau, P opulation Division: Tabl e 1: Annual Estimates of the Population for Counties of Florida: April 1, 2000 to July 1, 2005 (CO-EST2005-01-12), March 16, 2006.

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60 BIOGRAPHICAL SKETCH Brandy Sunshine DeArmond was born on January 10, 1978, in Leesburg, Florida. Relocating to the Tampa area when she was a toddle r, Brandy, the oldest of seven brothers and sisters, graduated from Hillsborough High School in 1996, where she was part of the swim team, French Club, and other extra-curric ular activities. She traveled to France in 1995 as part of an exchange program, and held an af ter-school job at a na tural foods store so she could buy her first car, a bright orange AMC Gremlin. While attending the Univer sity of South Florida, where she graduated in 2001 with a bachelo rs degree in geology, she held an internship w ith the Water Resources Division of the United States Geologic al Survey in Tampa. After graduating, she moved to Gainesville, Florida, wh ere she attended graduate school at the University of Florida, as part of the Department of Geological Scienc es. While in Gainesville, she also attended many concerts at local venues, dabbled in art and playing the drums, consorted and cavorted with her best friend Liz, and rode her clunky old bicycle as much as she could. In July 2004, she moved back to Tampa to work for an environmental consulting company, where she has performed field work in Florida and Georgia, completed contam inant delineation and remediation, and has also served as support for expert witnesses in litiga tion cases. In June 2007, her company transferred her to Golden, Colorado, where she and her boyfriend, Jason, enjoy camping in the beautiful Rocky mountains, fossil hunting, collecting rock s, listening to records, and exploring the multitude of local microbrews. She is currentl y looking forward to her first real winter and learning how to snowboard.