Title: Design and Operational Results for a Large Scale Wetland Treatment System: Figure 1: Distribution of Created Plant Communities and Sampling Station Location at the Iron Bridge Wetland System
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Title: Design and Operational Results for a Large Scale Wetland Treatment System: Figure 1: Distribution of Created Plant Communities and Sampling Station Location at the Iron Bridge Wetland System
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Language: English
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Spatial Coverage: North America -- United States of America -- Florida
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Abstract: Design and Operational Results for a Large Scale Wetland Treatment System: Figure 1: Distribution of Created Plant Communities and Sampling Station Location at the Iron Bridge Wetland System
General Note: Box 8, Folder 3 ( Vail Conference, 1993 - 1993 ), Item 13
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
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Bibliographic ID: WL00001299
Volume ID: VID00001
Source Institution: Levin College of Law, University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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MONITORING METHODS


Water quality monitoring was conducted on a monthly basis at the stations shown in Figure
1. The ten stations represent influent and effluent stations, and five internal strata as
defined below:


Stratum 1 is
Stratum 2 is
Stratum 3 is
Stratum 4 is
Stratum 5 is


represented
represented
represented
represented
represented


by station WP3;
by stations WP4 and WP5;
by station WP6;
by station MM8; and
by HS10.


Influent (WP1) and effluent (HS10) samples at the IBWTS were collected daily as 24 hour
composite samples, while the eight internal stations were collected as grab samples over a
three consecutive day period.


LAKE SHORELINE
HERPETOFAUNAL PITFALLS 7 Tm
FISH SIENING SITES
VERTEBRATE SITES
BERM


Figure 1. Distribution of created
the Iron Bridge Wetland Treatment


plant communities and sampling station locations at
System.


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RESULTS AND DISCUSSION


A summary of the IBWTS compliance data for the first four years of operation and the state
(FDER) permit criteria for the IBWTS effluent are shown in Table 1. This table shows the
TN and TP concentrations have been well below the permit limits during the first four years
of operation. The average annual TP concentrations have remained relatively stable since
start-up, with the average TP concentration of the four years shown in Table 1 being 0.087
mg/L The stability of the IBWTS TP concentrations contrast the results or opinions of
several studies in the literature, and this may be attributed to the operational procedures
employed at the IBWTS, and/or the comparative loading rates to the IBWTS. The average
annual TN concentration of 0.8 mg/L for 1991 was the lowest annual average concentration
since start-up of the IBWTS system. Lower TN loading rates to the IBWTS could be the
primary reason for the observed TN concentrations, however, there has been a general
downward trend in the TN concentrations at the IBWTS discharge station since October
1990, several months prior to the start-up of Phase III of the wastewater treatment plant
facility.

A comparison of the TN and TP concentrations for the IBWTS discharge and the upstream
(R1) and downstream (R5) stations in the St. Johns River (SJR) are shown in Table 2. The
data in this table shows a slight (insignificant) change in the upstream TN concentration for
1991 as compared to the 1990 value. The 1991 upstream and downstream TN
concentrations are statistically equal, while for the previous year there was a decrease in TN
concentration from the upstream to the downstream stations. A comparison of the data in
S Table 3 shows overall there was very little change in TN concentration from the upstream
station at the State Road 50 bridge to the downstream station on the north side of Puzzle
Lake over the period of 1985 to 1991.


Table 1. Comparison of the first four years of compliance data with the current permit
criteria. Flows shown represent influent discharges to the IBWTS.


Flow TN TP
(MGD) (mg/L) (mg/L)

FDER 13.00 2.31 0.200
1988 10.00 0.84 0.095
1989 13.33 0.92 0.076
1990 13.28 0.93 0.090
1991 12.90 0.80 0.087



In general, the TN characteristics of the IBWTS discharge have been equal to, or slightly
better than, the TN concentrations in the river. The seven year (1985-91) average TN
S concentration in the river calculated from the data in Table 3 is 1.15 mg/L, while the


.2.2








average TN concentration in the river for 1988-91 was 0.97 mg/L This compares to a 0.87
^ mg/L average TN concentration in the IBWTS discharge during the period of 1988-91,
making it very difficult to infer that the IBWTS discharge has negatively influenced water
quality conditions in the river. As an example, the discharge of IBWTS waters directly into
the river in 1991 would have resulted in a 0.0028 mg/L decrease in TN concentrations in
the river, assuming average conditions for both systems. Water from the IBWTS, however,
was not discharged directly to the river and consequently had no measurable effect on TN
concentrations in the SJR.


Table 2. Comparison of the annual average TN and TP discharge concentrations with the
annual averages of the receiving waters.


TN TP
Station' (mg/L) (mg/L)

1988 1989 1990 1991 1988 1989 1990 1991

HS10 0.84 0.92 0.93 0.80 0.095 0.076 0.090 0.087
SJR1 0.87 0.88 1.08 1.05 0.137 0.074 0.098 0.053
SJR5 0.87 0.89 0.89 1.09 0.149 0.071 0.084 0.116
SR 0.95 1.00 1.09 1.06 0.117 0.070 0.080 0.067

HS10 = IBWTS Discharge
SJR1 = Station in the St. Johns Upstream of HS10
SJR5 = Station in the St. Johns River Downstream of HS10
SR = Average Annual Concentration for Seminole Ranch



The TP concentrations shown in Table 3 follow the same general pattern as described for
TN above. The upstream average annual TP concentration for 1991 was the lowest annual
average measured since this study began in 1985. This observation may be partially
attributed to changes in management practices taking place in the flood plain upstream of
State Road 50, and most probably to the stage levels of the river throughout 1991. Calendar
year 1991 was the only year during this study where the average monthly gage heights
exceeded 5.0 ft. for the entire twelve month period. Each of the preceding six years had at
least three consecutive months where average monthly gage heights were below 5.0 ft.
Maintenance of the higher water levels in the flood plain during 1991 may have reduced
releases of TP from the sediments relative to previous years, in addition to providing greater
dilution of non-point discharges of TP to the basin and river.

The effects of the IBWTS TP discharge on the water quality conditions in the river are
basically unmeasurable, as shown for TN. If, however, the IBWTS discharged directly to
the river in 1991 near the upstream station, then the net effect on the TP concentrations in


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the river would have been a 0.0038 mg/L increase in TP concentration, assuming average
conditions prevailed throughout the year. This increase would have little effect on the
apparent net loading that occurred between stations R1 and R5 in 1991.

Table 3. Comparison of the average annual TN and TP concentrations, and average flow
rates for the upstream and downstream stations in the river.


TN TP
(mg/L) (mg/L)
Flow
Year (cfs) R1 R5 R1 R5

1985 1256 1.67 1.38 0.084 0.056
1986 724 1.61 1.70 0.162 0.150
1987 1335 0.90 0.86 0.133 0.121
1988 866 0.87 0.87 0.137 0.149
1989 638 0.88 0.89 0.074 0.071
1990 786 1.08 0.89 0.098 0.084
1991 1835 1.05 1.09 0.053 0.116
Average 1063 1.15 1.10 0.106 0.107



As shown in Table 3, 1991 was the first year where a significant increase in TP
concentrations occurred between the two river stations. The net TP loading from the
drainage basin to the portion of the river between stations R1 and R5 was 623 lb/day,
assuming no change in flow from station R1 to R5. The IBWTS TP loading, assuming direct
discharge to the main channel of the river, during 1991 would have accounted for 1.6
percent of the total loading in this reach of the river. In comparison, the IBWTS flow at
most accounted for 1.1 percent of the flow in the same reach (see Table 4), assuming no
other hydrologic inputs occurred between the stations R1 and R5. The effect of the IBWTS
TP inputs to the river decreases slightly when averaged over the four years since start-up.
In this case, the IBWTS TP load still accounts for about 1.6 percent of the annual load to
the reach between stations R1 and R5, however, the IBWTS flow now accounts for a
maximum of 1.9 percent of the total flow in the same reach, assuming no other hydrologic
inputs.

Water quality data related to the nitrogen analyses for the five strata are summarized in
Table 5. The data in Table 5 show three interesting changes from the previous year's
results. The first is the continued decrease in the IBWTS influent TN concentration from
4-5 mg/L initially, to the 1991 average annual concentration of 2.44 mg/L. This can be
directly attributed to the Phase II and III facilities going on-line at the Iron Bridge Regional
Water Pollution Control Facility (IBRWPCF). The decreasing TN concentration has
reduced the TN loading to the IBWTS from a high of 612 lb/day in 1989 to 262 lb/day in
^ 1991.








Table 4. Comparison of the average annual gage height and discharge rates at Station R1
( with IBWTS average annual discharge rate.


Discharge Rate (MGD)
Gage Height
Year (ft) Station R1 IBWTS

1985 5.22 812 0
1986 4.27 468 0
1987 5.35 863 0
1988 5.02 560 10.63
1989 4.34 412 13.91
1990 4.77 508 10.68
1991 6.70 1186 13.40
Average 5.10 687 12.16


A second noticeable change in the 1991 TN data set is the apparent decrease in the TN
uptake capacity for Stratum 1, as represented by station WP3. The 1991 average annual TN
concentration at station WP3 was the first since the IBWTS start-up that exceeded 2.0
mg/L, as shown in Table 5. This observation theoretically may be attributed to a saturation
of Stratum 1 to a point where TN input equals TN output (moving front concept), or to a
f" structural change in Stratum 1, or to a shift in management practices for this area. The first
postulate seems unreasonable since TN is not a conservative part of the nutrient cycle in
wetlands, and the system is only four years old. The second also seems unreasonable at this
point, since the 1992 TN data collected through October 1992 indicates a 1.1 mg/L average
annual TN concentration at station WP3.

Table 5. Comparison of the TN annual averages through the IBWTS for the first four years
of operation.


Nitrogen
Station (mg/L) Area'

1988 1989 1990 1991

WP1 4.18 5.52 2.83 2.44 0
WP3 1.53 1.92 0.98 2.20 11
WP4,5 1.51 1.74 1.00 1.02 16
WP6 1.27 1.59 1.09 1.11 32
MM8 0.96 1.22 1.19 1.25 67
HS10 0.84 0.92 0.93 0.80 100

1 Area equals the percent of wetland area upstream of the listed sample station.


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The final observation for the 1991 data set relates to the observed TN uptake rate for
S Stratum 2. The 1991 average loading rates of 3.57 lb/acre/day to Stratum 2 were the
highest since start-up of the IBWTS. The resultant 1991 average annual TN uptake rate for
Stratum 2 was within the range of the rates for Stratum 1 during the previous three years.
The rate of change for TN concentration in Stratum 2, however, appeared to be much
higher than the rates for Stratum 1.

Water quality data related to the TP analyses for the five strata are summarized in Table
6. The data in Table 6 shows similar changes from the previous years results as those
described for TN. Table 6 shows relatively consistent results for the annual average TP
concentrations leaving the five strata, with the exception of Stratum 1. As for TN, there was
a continued decrease in the IBWTS influent TP concentration from 0.6-0.7 mg/L initially
to the 1991 average annual concentration of 0.23 mg/L Once again, this can be directly
attributed to the Phase II and III facilities going on-line at the IBRWPCF.

Table 6. Comparison of the TP annual averages through the IBWTS for the first four years
of operation.


Phosphorus
Station (mg/L) Area1

1988 1989 1990 1991

WP1 0.572 0.720 0.410 0.230 0
WP3 0.103 0.080 0.160 0.370 11
WP4,5 0.102 0.065 0.140 0.120 16
WP6 0.106 0.070 0.110 0.110 32
MM8 0.091 0.050 0.050 0.060 67
HS10 0.095 0.076 0.090 0.087 100

1 Area equals the percent of wetland area upstream of the listed sample station.


The apparent decrease in the TP uptake capacity, and concurrent increase in TP
concentration releases, for Stratum 1 as represented by station WP3, was a more significant
event than for TN. Previous studies have discussed the implications of TP being essentially
a conservative element within a wetland system. This makes the concept of a moving TP
front more of a management concern than would have been expected for TN.

The 1991 average TP uptake rate for Stratum 1 was the first since the IBWTS start-up that
showed a net discharge of TP, as shown in Table 6. This observation theoretically may be
attributed to a saturation of the TP storage sites in Stratum 1, or to a shift in management
practices for this area, or potentially to a structural change in the structure of Stratum 1 that
increased the release of TP to a greater level than the uptake rates.


I~lo








The 1992 data collected through October, however, does not support the theory of a moving
front, or that the TP storage capacity of Stratum 1 was exhausted in 1991. The ten month
average annual TP concentration of 0.11 mg/L for Stratum 1 is statistically similar to the
average TP concentrations seen prior to 1991. This indicates that Stratum 1 had a net
uptake and storage of TP through the first ten months of 1992. This contradicts the moving
front theory or the assumption that the TP storage capacity of Stratum 1 was exhausted at
some point in 1991. Instead, the 1992 data indicates that the apparent TP uptake rate in
Stratum 1 was related to the distribution, density, and type of vegetation (including
associated micro-organisms) within the treatment cell.




CONCLUSIONS

The results observed for the IBWTS indicate that wetlands can function as part of the
wastewater treatment process. The IBWTS provides a cost effective mechanism that has
consistently reduced nutrient concentrations in the wetland discharge to background levels.
The IBWTS also has produced a relatively consistent TN and TP output concentration
during the first four years of operation. The IBWTS discharge has had no measurable effect
on the SJR, and most likely would not affect water quality in the river even with a direct
discharge to the main channel. The current discharge practice of routing water from the
IBWTS across an adjacent natural wetland, and then into back water areas of the SJR,
serves as a form of reuse. Similar uses of wetland systems that allow for surface discharge
offer one of the most cost effective disposal options for entities operating wastewater
treatment facilities.

Management procedures may be one of the most important factors controlling long term
nutrient uptake and storage by a wetland. The changes in the nutrient uptake capacities
observed for the first cell of the IBWTS during 1991 were attributed to altered management
practices for this cell. Increased water depths led to changes in the vegetative community
in the first cell that correlated to the changes in nutrient uptake. Restoration of the original
vegetative community in early 1992 reestablished the nutrient uptake rates. These patterns
indicate that operation and management practices may significantly affect both the
instantaneous and long term nutrient uptake rates for wetland treatment systems.

A secondary benefit of using wetlands for wastewater treatment was their ability to provide
wildlife habitat. The IBWTS has expanded the available habitat for many wetland
dependent wildlife species in east Orange County. As an example, the number of bird
species that have been observed on the IBWTS site was over 140 through the summer of
1992. At least 12 state and/or federally listed wildlife species utilize the IBWTS as foraging
or nesting habitat. This makes the IBWTS a form of large scale wetland restoration which
is extremely desirable considering the acreage of wetlands that have been lost to
development during the past 100 years.



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