David P. Krabbenhoft, George R. Aiken
The major objectives of this project are to use an integrated biogeochemical approach to examine: (1) anthropogenic-induced changes in the water chemistry of the Everglades ecosystem, (2) biogeochemical processes within the ecosystem affecting water chemistry, and (3) the predicted impacts of restoration efforts on water chemistry. The project uses a combination of field investigations, experimental approaches (mesocosm experiments in the ecosystem, and controlled laboratory experiments), and modeling to achieve these objectives. Contaminants of concern will include nutrients, sulfur, mercury, organic compounds, and other metals. Protocols for the collection of samples and chemical analyses developed during earlier studies will be employed in these efforts. Integration of the individual tasks within the project is achieved by colocation of field sampling sites, and cooperative planning and execution of laboratory and mesocosm experiments. Results from all tasks within the project are archived within a single database for use in Decision Management GIS systems and ecosystem models.
Spiker, Elliott C., Holmes, Charles W.
Aiken, G. R., Ryan, J. N.
The entire paper is available from the Environmental Science and Technology Journal web site; however, a journal subscription is required.
Orem, W. H., Harvey, J.. W., Spiker, E. C.
Lerch, Harry E., Rawlik, Peter
Holmes, C. W., Kendall. C., Lerch, H. E., Bates, A. L., Silva, S. R., Boylan, A., Corum, M., Marot, M., Hedgman, C.
Orem, William H., Harvey. Judson W., Spiker, Elliot C.
Kotra, R. K., Holmes, C. W., Orem, W. H., Hageman, P. L., Briggs, P. H., Meier, A. L., Brown, Z. A.
During FY02, mesocosm experiments were conducted at several sites in the Everglades to test the effects of sulfate addition (3 concentration levels), inorganic mercury (3 concentration levels), DOC (2 concentration levels), inorganic mercury plus sulfate (3 concentration levels), and inorganic mercury plus DOC. Following the additions, changes in chemical species (methylmercury and other mercury species, sulfur species, DOC, nutrients, anions, cations, Fe and Mn, redox, conductivity, pH) and microbial activity (sulfate reduction and mercury methylation rates) are determined in surface water, porewater, and sediments in the mesocosms over time (usually followed for several months following the start of the experiment).
In FY02, we conducted laboratory microcosm experiments to examine the effects of drying and rewetting of Everglades’ peats on methylmercury production, mercury geochemistry, sulfur geochemistry, and nutrients.
The experimental approach to drought/burn and rewet experiments involves: (1) collection of a series of small cores from two sites (WCA 3A-15, and STA-2), (2) drying of these cores for different times in a laboratory under controlled conditions, (3) rewetting of these cores with water collected at the two core collection sites, and (4) analysis of surface water, porewater, and sediments in the rewetted cores at intervals of time following rewetting. Analytes measured in the samples included methylmercury and other mercury species, sulfur species, nutrients, anions, cations, DOC, and sediment parameters (organic carbon, total N, total P, total S, S species). Biological parameters measured included methylmercury production and sulfate reduction rates. The initial experiment was begun in March 2002 and is scheduled to end in September 2002.
1. Mesocosm Studies Mesocosms are left open to the outside environment until experiments are to be run. During experiments, mesocosms are closed off and chemical additions are made to sets of mesocosms to test the effects of the chemical additions on methylmercury production. Each chemical addition (variable) is tested at multiple concentration levels. In some sets of mesocosms, multiple chemical species are added to examine interactive effects.
We also propose to follow-up on our previous mesocosm studies on methylmercury production. Experiments will be repeated in order to verify and expand on results from FY02. A new feature in FY03 will be the use of isotopically labeled sulfate in the chemical additions to follow changes in sulfur geochemistry and its effects on methylmercury production. Our previous mesocosm experiments were focused in the northern Everglades. In FY03 we plan to add another mesocosm site in an STA (probably STA-2). These constructed wetlands can behave as zones of low methymercury production (such as ENR), but also can produce very high levels of methylmercury (STA-2). The reasons for this are not fully understood, and mesocosm experiments in the STA’s will be designed to provide managers with information on how best to operate the STA’s to minimize methylmercury production. Completed 2003
2. ) Drought/Burn and Rewet Experiments We will continue to analyze samples from the first drought/rewet experiment that ended in September 2002. Results from all experiment PI’s will be combined in a database, and a series of publications on the results will be written up for publication. A follow-up experiment will be conducted in FY03 (continuing into FY04) using a larger core approach at two new sites (a high sulfur and low sulfur site in the northern Everglades). The larger cores will slow down the drying process in the lab, and more closely simulate conditions in the ecosystem. Additional changes to the follow-up experiment will include shorter dry times and extended sampling times following rewet. Results will provide ecosystem managers, and CERP/GEER planners with information on how to limit the effects of drought and rewet cycles on methylmercury production. Results will be especially useful for managing STA’s and northern WCA 3, areas that experience more frequent drought/rewet cycles.
3. Nutrient and Sulfur Sources in Big Cypress Surface water, groundwater, porewater, and sediment cores will be collected from sites throughout the Big Cypress Preserve. Although much of Big Cypress is a sandy soil, there are areas where peat or peaty muck is present and shallow cores and porewater can be obtained. Groundwater will be obtained from existing wells in the Preserve. Samples will be analyzed for nutrients (carbon, nitrogen, and phosphorus), sulfur species, sulfur isotopic composition, uranium, and uranium activity ratio. The uranium and uranium activity ratio is used as a tracer for phosphorus sources. Orem, Zielinski, and Simmons have used this approach successfully to examine the sources of phosphorus to the northern Everglades, and to the rivers north of Lake Okeechobee. This approach can differentiate uranium (and phosphate) originating from agriculture, groundwater, and background. Similarly, sulfur isotopes will be used to trace the sources of sulfur entering Big Cypress. Orem/Bates/Lerch previously used sulfur isotopes to trace the sources of excess sulfate entering the northern Everglades.
In FY03 work will focus on sampling at selected sites throughout the Preserve, and chemical analysis of the samples. The study area will extend from the agricultural region north of the Big Cypress Preserve to the Ten Thousand Islands Area in the south. Sites will be primarily accessed by ground vehicle, but we will also explore possible helicopter support from the Big Cypress National Preserve for accessing more remote sites. Preliminary studies completed in 2003.
4.Aquifer Storage and Recovery (ASR) Water Quality Sampling of ASR experimental sites will be done in collaboration with the ASR science team, and with other members of this project looking at mercury (Krabbenhoft) and DOC (Aiken) water quality issues related to ASR. Sulfur species will be collected using a standard sampling protocol and analytical scheme, similar to that used in our work on sulfur contamination from canal discharge. In addition to sulfur species (sulfate, sulfide, thiosulfate, sulfite, total S), we will also examine the isotopic composition of the sulfur in the ASR water. This could then potentially be used to examine the fate of sulfur released from ASR water into the ecosystem. Sulfur isotope analysis delta 34S will involve isolation of the sulfate or sulfide using a precipitation approach, and measurement of the isotopic composition of the sulfur using isotope ratio mass spectrometry. We have used this approach previously to trace the sources of sulfur entering the Everglades.
Work on sulfur in ASR water in FY03 involves collaborative sampling with Krabbenhoft, Aiken, and others at selected ASR test sites. A series of preliminary samples will examine the range of sulfur concentration and speciation in ASR water, and the isotopic composition of this water.
5.Florida Bay Mercury Methylation and Sulfur Biogeochemistry The ACME II group (Krabbenhoft/Orem/Aiken) will examine the biogeochemistry of mercury methylation in Florida Bay sediments using a multifaceted field approach. This task will concentrate on evaluating the biogeochemistry of sulfur in Florida sediments and porewater. We will examine sulfur speciation and concentrations in sediments and sediment porewater. We have previously sampled in Florida Bay (1996-2001) and are familiar with the problems of coring and porewater extraction in the carbonate ooze underlying much of the bay. We will use an analytical scheme for sulfur speciation and quantification of sulfur species that we used previously in the Everglades and Florida Bay.
FY03 Work - Preliminary coring and porewater sampling to be conducted at selected sites nearshore and offshore in Florida Bay. Sampling to be conducted in collaboration with Krabbenhoft and Aiken.
1. MeHg mesocosm studies
The proposed 2003 mesocosm experiments will be conducted at the 3A-15 site in the central Everglades, that provided the highest MeHg response in the 2002 experiments, and also provides an ideal location for the DOC and sulfate addition experiments, and for the sulfur toxicity experiments described later. MeHg mesocosm experiments will be conducted between mid June and the end of October 2003. Conducting the experiment during this wet season/summer period should produce the maximum MeHg production signal, due to overall higher microbial activity in summer months. Mesocosms used in the experiment will either be newly purchased or previously used mesocosms that have never had mercury isotopes added (such as controls, sulfate only, or DOC only additions). All previously used mesocosms will be relocated at the 3A-15 site for this experiment. Installation of the new mesocosms and relocation of existing mesocosms (some moved from other sites in the Everglades) took place during mid-April 2003 to allow time for reequilibration of the sediment and water prior to initiating the experiment in June. After installation, mesocosms are left open (six two-inch breather holes drilled on the perimeter of each mesocosm) to its surroundings, which allows for free exchange of water. At the start of experiments, the holes are plugged with silicone stoppers to isolate the interior environment of the mesocosm from the surroundings and maintain the presence inside the mesocosm of the chemical.
Ten mesocosms will be used for sulfate plus mercury additions. The ten mesocosms will be grouped in sets of two for addition of sulfate at five different dosing (i.e. concentration) levels and a single mercury level of 1X ambient atmospheric (22 ug/m2; or 14.3 ug Hg). Experiments performed in 2000-2002 have adequately defined the mercury-only addition response over a range of 0 to 2X ambient dosing level. The sulfate dosing levels are 4, 8, 12, 16, and 20 mg/l, based on the results of our 2002 mesocoms. The sulfate is added to the mesocosms as sodium sulfate dissolved in site water. The appropriate amount to be added to each mesocosm to reach the target concentration is calculated based on the volume of water in each mesocosm. Each dosing level has a duplicate mesocosm for quantifying natural variability in the response, which is epically high for sediment-based measurements (e.g., net methylation rates). A group of 6 mesocosms (three sets of duplicates for each dosing level) will be used to examine the effects of DOC and mercury isotope dosing at 3 different dosing levels. DOC isolated from eutrophied sites near canal discharge in Water Conservation Area 2A will be used for the experimental dosing. Target addition levels for DOC will be about 30, 40 and 50 mg/l. The DOC is added to the mesocosms as a concentrated solution and mixed by gentle stirring of the surface water. Finally, a group of two mesocosms will have DOC, sulfate, and mercury isotope added. These mesocosms are intended to evaluate the synergistic effects of sulfate, DOC, and mercury on MeHg production. The dosing level to be used in this mesocosm pair will likely be about 14.3 ug Hg, 12 mg/l sulfate and 40 mg/l DOC. As with previous mesocosm experiments, we will employ control mesocosms to monitor the natural variability in the system and to evaluate whether there are any unnatural 'mesocosm' effects. To establish natural variability and to control for mesocosm effects, two mesocosms will be set aside as controls, and in addition two sites will be established in the marsh near the control mesocosms as ambient controls. The mesocosm controls will be plugged with silicone stoppers and treated in a fashion similar to the experimental mesocosms, but no dosing of any kind will be added.
The experiment will commence on June 23, 2003. Samples of surface water, porewater, Gambusia and sediments will be collected at the mesocosm and outside controls to define the initial conditions of the site. After sampling, all mesocosms will be plugged, and appropriate chemical doses will be added. Follow-up sampling of the experimental mesocosms, mesocosm controls, and outside controls for surface water, porewater, Gambusia, and sediments will continue on days 1, 61, and 119. After the initial doses, subsequent sulfate dosing is scheduled for days 14, 28, 42, 63, 78, 91, and 105. Surface water is collected by a peristaltic pump, and porewater (5 cm sediment depth) using a pump and a micropiezometer. In-line filtering is used for all porewater and surface water collections. Mercury-clean procedures are followed for all sampling, which provides minimal contamination acceptable for all analytes. Sediments are collected using a small push core to minimize disturbance of the mesocosm interior. Analytes measured in surface and porewater include: total mercury and MeHg (ambient pools and isotope spikes), anions, cations, sulfur species (sulfate, thiosulfate, sulfite, sulfide), nutrients (nitrate, ammonium, and phosphate), DOC, iron and manganese, redox, dissolved oxygen, and pH. Sediment geochemical analyses include: total mercury and methylmercury (ambient pools and isotope spikes), total sulfur, sulfur species (AVS, sulfate, disulfides, and organic sulfur), total and organic carbon, total nitrogen, total phosphorus, and metals. Sediments are also measured for various microbial parameters, including mercury methylation rate, and sulfate reduction rates. Time-sensitive parameters are measured in motel-room laboratories within hours of sample collection. Samples for later analyses are stored in an appropriate fashion (frozen, cool, etc.) and shipped back to laboratory facilities at the various PI’s labs (Middleton, WI; St. Leonard, MD; Reston, VA; Boulder, CO). At the termination of the experiment (currently scheduled for October 14, 2003), the silicone stopper plugs are removed from the mesocosms, and all equipment is removed from the site, with the exception of mesocosms, which are left in place for potential future studies.
2. Sulfur toxicity mesocosm experiments
To test the hypothesis that high sulfide levels have played an important, yet previously unrecognized, role in the proliferation of cattail in heavily S and P contaminated areas of the Everglades we propose to employ mesocosms and sulfate dosing in sawgrass and cattail dominated sites of WCA3A. The sites will be in relatively close proximity to each other, probably near tree islands where cattails are often found. Mesocosms would be installed at these sites and allowed to equilibrate for a period of couple months. As with the other mesocoms (described above), holes in the sides of the mesocosms would allow exchange of water with the outside during this equilibration period. The experiment would involve addition of sulfate at three levels: 100 mg/l, 50 mg/l, and 20 mg/l; each level run in triplicate. A pair of control mesocosms would also be run at each site (no sulfate addition). A pair of external control sites (no mesocosm, monitoring of external environment) would also be employed at each location (cattail and sawgrass). Sulfate added to each mesocosm would be calculated based on the volume of water at the time of the experiment, and the amount needed to bring the mesocosms up to the desired concentrations. Sulfate additions would initially be conducted biweekly, and sulfate concentrations monitored to determine future addition needs. Surface water in each mesocosm and in controls (mesocosm and external controls) would be routinely collected (biweekly to monthly) and analyzed for anions, cations, and nutrients. More intensive sampling of surface water, and pore water, and biological sampling would be conducted at least 4 times per year during the initial period of the experiment. Surface and pore water will be analyzed for sulfur species, anions, cations, and nutrients. Biological studies to be conducted would include rates of respiration and photosynthesis in macrophytes, abundance and types of periphyton on submerged periphytometers, and numbers and types of macroinvertibrates. We anticipate that the toxicological effects to plants may require many months to be detectable, and therefore we are planning for this experiment to run for two years. At the end of the study, intensive surface water, pore water, sediment, and biological analyses will be conducted. Coring and removal of plants from the mesocosms for further study will be conducted at this time.
3. Developing a predictive model for MeHg production in the Everglades and Stormwater Treatment Areas (STAs)
We propose a set of studies conducted over two years that are designed to produce a predictive model for MeHg production in the STAs. The study will be carried out via agreements with USGS researchers and with the Academy of Natural Sciences Environmental Research Center (ANSERC) in St. Leonard, Maryland. The objective of this study is to develop a predictive capability based on soil geochemistry, quality of inflowing water, and hydrologic conditions. Although this research arises from the need to manage existing STAS, it will also be useful in site selection for any future treatment areas and for planning and operation of future water reservoirs. We intend to apply our knowledge of MeHg production gained in the Everglades to the STAs, through collection of comparative soil data for the STAs, and by additional study of the influence of drying and wetting cycles across a wider range of soil types. This new work will provide information toward management of MeHg production in existing and planned STAs of different soil types, through site selection, control of hydrology, and water quality. The proposed study has the following components:
STA soil geochemistry - This component consists primarily of a field survey of soil geochemistry, especially sulfur, iron, and Hg/MeHg content, across the STAs. The objective of this survey is to test our Everglades-based understanding of MeHg production in the STAs. The primary drivers of MeHg within Everglades surface soils are sulfur, Hg, organic carbon and hydrologic conditions. A survey of soil conditions within the STAs will allow us to determine if the same drivers operate in STA soils, with their different land-use and hydrologic-maintenance histories. Currently operating STAs would be examined first in summer/fall 2003, then the survey would be expanded to STAs under construction and planned for construction in spring 2004. Site-selection criteria would include examination of a wide variety of soil and land-use types, and the management needs of the agencies responsible for Everglades restoration planning and operation. Specific objectives of this component are to provide baseline data for geochemistry and Hg/MeHg content of STA soils, and to evaluate the ACME conceptual model for control of MeHg production in Everglades soils for STA soils. Six sites within the STAs will be examined in fall 2003 and six more in 2004. Site access will be via helicopter. Mercury and MeHg will be measured in surface soils, interstitial waters, surface waters, periphyton and gambusia. Other standard ACME analytes to be measured include for bulk sediment: total sulfur, acid volatile sulfide, chromium reducible sulfur, organic sulfur, organic carbon, bulk density, and moisture content. Surface waters and pore waters will be analyzed for sulfate, partially reduced sulfate species, sulfide, total iron, total manganese, and dissolved organic carbon using the previously referenced methods.
Soil biogeochemistry at ACME Everglades sites - The ACME project examined eight discrete Everglades sites (ENR 103, F1, U3, 2BS, 3A15, 3A33, TS7, and TS9) in detail, 2-3 times per year from 1995 through 1998, and that covered most of the north-to-south extent of the ecosystem. These data have been used to generate a general conceptual model for control of MeHg production in the Everglades. There are a number of reasons to look at the sites again in 2003. First, decreases in MeHg in fish and wading birds have been observed in many areas of the central Everglades during that time period, but there is no information on any changes in MeHg in soils and water from the ACME sites. Second, additional data density, especially during a different hydrologic period, will provide a more robust data set for comparison with STA soils, and diagenetic modeling. Last, there are some additional parameters that are needed for the diagenetic model that were not collected during 1995-1998, particularly solid-phase Fe speciation, which is needed to model microbial Fe reduction. Periodic resampling of the ACME sites is relatively inexpensive, and will provide valuable long-term data on changes in Hg cycling in the Everglades ecosystem. Sampling conducted at site ENR103 will provide valuable insights into STA biogeochemistry after several years of operation, particularly how long-term sulfate loading has impacted geochemistry and MeHg production in this soil. ENR soils were agricultural prior to conversion, and the high S content of these soils has minimized MeHg production at this site since start-up. Specific objectives of this component are: (1) measure Hg/MeHg concentrations in soils, soil interstitial waters, surface waters and gambusia at the eight main ACME sties; (2) examine potential changes in MeHg concentrations at ACME sites, in comparison with declines in MeHg in wading bird and largemouth bass in the central Everglades; (3) examine changes in soil geochemistry and MeHg in response to changing flow patterns and sulfate loading, particularly in 2BS where substantially increased sulfate loading has occurred since 2000; and, (4) collect information on iron cycling that is needed for construction of the diagenetic MeHg model. Six to eight ACME sites in the Everglades will be revisited in June or July of 2003. Sites will include ENR103, F1, U3, 2BS, 3A33, 3A15, TS7 and TS9. Site access will be via helicopter. Mercury and MeHg will be measured in surface soils, interstitial waters, surface waters, periphyton and gambusia. Other standard ACME analytes to be measured include for bulk sediment: total sulfur, acid volatile sulfide, chromium reducible sulfur, organic sulfur, organic carbon, bulk density, and moisture content. Surface waters and pore waters will be analyzed for sulfate, partially reduced sulfate species, sulfide, total iron, total manganese, and dissolved organic carbon using the previously referenced methods.
Examination of the influence of drying and wetting cycles across a wider range of soil type - This work will be an extension of successful studies of the effects of drying and rewetting in STA 2 Cell 1, where substantial MeHg production following rewetting was documented. We hypothesize that the pulse of methylation activity after rewetting of Everglades and STA soils is fueled by sulfate generated from the oxidation of reduced sulfur in soils during the dry period. In order to follow up on this finding, we conducted controlled drying and rewetting studies in the laboratory with soils from STA2 Cell 1 in spring 2002 and again in winter 2002/2003. Results from the spring 2002 experiment support the hypothesis, whereby large increases in sulfate concentrations in dried and rewet cores from both sites were observed. Analysis of samples from the spring 2003 experiment is underway. During the spring 2002 experiment, MeHg increased significantly in soils from both sites within 5 days of rewetting dried cores, and stayed roughly the same over the next six weeks. Water column MeHg concentrations lagged a bit behind soil, as MeHg in water derived from production in and flux from soils. The pulse of MeHg production following rewetting was rapid, but MeHg concentrations in surface soils remained high for at least six weeks following rewet. MeHg concentrations in water over cores were maximal in 3A15 cores 3-4 weeks after rewetting, but continued to increase in STA2 cores for at least 6 weeks. This study confirmed that the high MeHg concentrations observed in STA2 Cell 3 result from in situ production in surface soils immediately following rewetting. The soil chemistry at STA2 Cell 3 is ideal for MeHg production, which is further fueled by the addition of high sulfate canal waters to the STA. In situ MeHg concentrations in the STA2 soils were higher than the 4-year average for the ACME sites of highest MeHg production in the Everglades. The % MeHg at STA2 cores after drying and rewetting substantially exceeded the the average %MeHg for the high MeHg sites in the WCAs. However, both soils examined in these experiments were relatively low S soils. Some of the largest responses in MeHg to drying and rewetting cycles in the Everglades have been in the high S northern Everglades. We believe that it is important to quantify experimentally the response of higher S soils to drying and rewetting in order to adequately model MeHg production within the STAs. We propose to use the same sample design used in spring 2003 to make these measurements, using high S soils from STAs that have been constructed from agricultural lands. Two additional soil types would be examined. This work is to be undertaken in winter 2004/2005. Sites will be chosen after completion of the STA soil survey and in consultation with SFWMD. Specific objectives of this component are: (1) examine the magnitude and timing of MeHg production in response to drying and rewetting cycles across a wider range of STA soil types, particularly high S-content soils; and (2) compare the response of high and low S soils to drying and rewetting, and apply this understanding to management questions for the STAs. Experimental studies of the influence of soil drying and rewetting on MeHg production will be done using the same design and facilities used in for spring 2003 experiments. Cores will be collected in Florida and driven to ANSERC, where they will be dried in a temperature and light-controlled environment. The amount of drying time will be determined after final analysis of the spring 2003 experiments, in which cores were dried for months before rewetting, in order to provide a comparison with cores that had been dried for a few weeks (spring 2002 experiments). Replicate soils cores (~40) will be collected intact from each of chosen sites. In addition to cores collected for laboratory experiments, additional samples will be taken to assess mercury and sulfur biogeoch
4. Field studies
Big Cypress National Preserve(BCNP) - A preliminary surveys in BCNP in FY03 was conducted to examine concentrations and sources of nutrients and sulfur. Results showed levels of nutrients, sulfur, and MeHg to be generally low, except in the area around the L-27 feeder canal. This canal had relatively high S and P levels. Plans to divert water from this canal into BCNP could, therefore have significant consequences with respect to eutrophication and MeHg production in this currently pristine area. We propose to follow up on this preliminary work in FY04 with more detailed studies, especially in the region of the L27 feeder canal. We will collect surface water, groundwater, porewater, and sediment samples from selected sites in BCNP, and analyze them for nutrients, sulfur species, sulfur isotopic composition, uranium, and uranium activity ratio. Uranium and uranium activity ratio is used as a tracer for phosphorus sources (agriculture, groundwater, background). Similarly, sulfur isotopes will be used to trace the sources of sulfur entering Big Cypress.
Canals - Canals draining the EAA and entering the Everglades are the principal conduit for many of the important contaminants entering the ecosystem. Although the SFWMD monitors the canal system for P and other constituents, monitoring of the canal system for S is lacking. Since 1998 we have been conducting routine monitoring of the canal systems for S concentrations and isotopic composition. This will provide background data for models of S entering the ecosystem. We plan to continue this work.
Florida Bay - This task will examine sulfur speciation and concentrations in sediments and sediment porewater. We will use an analytical scheme for sulfur speciation and quantification of sulfur species that we used previously in the Everglades and Florida Bay. The range of concentrations and biogeochemical processes involved in MeHg production in the bay may be quite different from those in the freshwater Everglades. This study will provide baseline data for developing a conceptual model of the mechanism og MeHg production in Florida bay sediments.
Transect studies in Everglades National Park (ENP) and Loxahatchee National Wildlife Refuge (LOX) - These studies will examine changes in water quality along selected transects in both ENP and LOX. The ENP studies will focus on transects near the area where water from the L67 canal is discharged into the Park. Preliminary studies conducted by the South Florida Water Management District have identified another MeHg 'hot spot' near this zone of discharge. Previous USGS work has shown that the L67 canal has significant sulfate levels, possibly originating from the Miami Canal. This sulfate could be stimulating sulfate reduction and MeHg production at the L67 discharge site. This work will examine the distribution of MeHg production, and sulfur geochemistry in the targeted area, and determine the causes of the MeHg 'hot spot'. We will also explore ways to mitigate MeHg production in the target area of ENP. The studies in LOX will focus on transect work from the edges of LOX near newly established STA’s, to the center of the refuge. Preliminary studies suggest that leakage of contaminated water across the levees bounding LOX is occurring. Contaminants entering the refuge include major cations, sulfur, Hg, anions, and nutrients. These contaminants may have significant impacts on water quality within LOX, with largely unknown impacts on biotic assemblages within the refuge. This study will provide basic information on changes in water quality parameters in the refuge. Work is planned to be coordinated with Paul McCormick, USGS, BRD.
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