William H. Orem, George R. Aiken, Cindy Gilmour (Academy of Natural Sciences)
Presently, we are addressing several major questions surrounding the mercury research field, and the Everglades Restoration program: (l) What, if any, ecological benefit to the Everglades would be realized if mercury emissions reductions would be enacted, and over what time scales (years or tens of years) would improvements be realized? (2) What is the role of old mercury (previously deposited and residing in soils and sediment) versus new mercury (recent deposition) in fueling the mercury problem? (3) In the present condition, is controlling sulfur or mercury inputs more important for reducing the mercury problem in the Everglades? (4) Does sulfur loading have any additional ecological impacts that have not been realized previously (e.g., toxicity to plant and animals) that may be contributing to an overall decreased ecological health? (5) Commercial fisheries in the Florida Bay are contaminated with mercury, is this mercury derived from Everglades runoff or atmospheric runoff? (6) What is the precise role of carbon (the third member of the 'methylmercury axis of evil', along with sulfur and mercury), and do we have to be concerned with high levels of natural carbon mobilization from agricultural runoff as well? (7) Hundreds of millions of dollars are being, or have been spent, on STA construction to reduce phosphorus loading to the Everglades, however, recently constructed STAs have yielded the highest known concentration of toxic methylmercury; can STA operations be altered to reduce methylmercury production and maintain a high level of phosphorus retention over extended periods of time? The centerpiece of our research continues to be the use of environmental chambers (enclosures or mesocosms), inside which we conduct dosing experiments using sulfate, dissolved organic carbon and mercury isotopic tracers. The goal of the mesocosm experiments is to quantify the in situ ecological response to our chemical dosing, and to also determine the ecosystem recovery time to the doses.
Aiken, G. R., Ryan, J. N.
Orem, W. H., Harvey, J.. W., Spiker, E. C.
Lerch, Harry E., Rawlik, Peter
Orem, William H., Harvey. Judson W., Spiker, Elliot C.
Cox, T., Spencer, R.
Kotra, R. K., Holmes, C. W., Orem, W. H., Hageman, P. L., Briggs, P. H., Meier, A. L., Brown, Z. A.
Hurley, J. P., Olson, M. L., Cleckner, L. B.
Began dual sulfur-DOC controlled laboratory experiment to help design field-enclosure scale deployment of these tests. Tests were to be carried out by another investigator in collaboration with Orem, Krabbenhoft, Aiken, Hurley and Gilmour. All of these primary investigators have agreed to make facilities and materials available for these studies, such as Hg isotopes and analysis (Krabbenhoft), methylating bacteria (Gilmour), DOC fractions (Aiken) and laboratory space (Orem). To bring these tests from the laboratory scale the field scale, large quantities of the various DOC fractions will need to be isolated in a trace-metal clean manner to provide enough material for testing. Preliminary work wasplanned for 5/00 and 7/00 in collaboration with Krabbenhoft, Gilmour, and Aiken.
Examined rates of mercury methylation and release of P, N and S from fire events. This followed up on preliminary work conducted in FY 99 on fires in the northern part of WCA 3. We plan to conduct laboratory simulations of fire and rewetting events to examine remobilization of nutrients following fire or extended dry periods when peat oxidation may occur. Field studies of nutrient remobilization following fire or drying events and rewetting were conducted in field enclosures, and in actual burned or dried natural areas as circumstances permited
Examine sulfur concentrations, speciation, and distribution in field-enclosure studies (coordination with mercury field-enclosure studies). The purpose of the field-enclosure work will be to examine how changes in environmental parameters accompanying the restoration effort will affect sulfur geochemistry. Field-enclosure sites were selected to represent various types of environments in the Everglades, such as eutrophic sites, oligotrophic (background) slough/marsh sites, and marl prairies.
Initial installation of small enclosures (USGS) and initial experiments in large (SFWMD enclosures) planned for 5/00, with follow up work in 7/00 and 9/00. Enclosure experiments expected to continue into FY01.
We are currently using environmental enclosures placed in the ecosystem (mesocosms) to examine the effects of changing water quality variables on methylmercury production and bioaccumulation. These experiments are designed to examine the effects of individual variables and multivariable interaction effects on methylmercury production. Variables of interest with regard to methylmercury production include: inorganic mercury (added in isotopic form), sulfur, nutrients (especially phosphorus), DOC, and iron.
Our experimental mesocosms have “breathing holes” that are left open to the outside environment during the intervening time between experiments so that the enclosed areas can equilibrate with the native environment. Our observations (direct measurements of pH, dissolved oxygen, temperature, and observations of general visual health) have shown that the leaving the mesocosms enclosed for 2-4 months does not produce an artificial “mesocosm effect” and bias our results. During experiments, the breathing holes are closed with silicone stoppers 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. For example, 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 addition, during each experiment we establish at least two control mesocosms to check for enclosure effects, and we take samples from the native environment near the mesocosms to assure that the mesocosms are tracking the overall season changes that are observed annually in the ecosystem. Results of mesocosm studies from FY01 and 02 show that: (1) introduced or “new” inorganic mercury is methylated preferentially over “old” mercury bound in the sediments, and this new mercury is bioaccumulated up to native fish preferentially as well; (2) Sulfate addition stimulates methylmercury production, but sulfate and inorganic mercury additions stimulate even higher methylmercury production; (3) Sulfide appears to inhibit methylmercury production to some extent. (4) DOC addition enhances methylmercury concentrations in surface water in two ways: first by enhancing availability of new mercury to methylating bacteria (directly or indirectly), and second, by increasing the net overall solubility of the produced methylmercury into the water column.
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. The Everglades Mercury Cycling Model has a major information gap in that it does not directly simulate sulfur cycling and linkages to methylation, primarily due to a lack of previous research on sulfur cycling rates, fate and speciation. Our previous mesocosm experiments were focused in the northern Everglades. In FY03 we propose 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.
Phase I ACME showed a very dramatic (about a 10-100X increase) effect of drying and rewetting cycles on methylmercury production bioaccumulation in fish in the Everglades. Detailed geochemical examinations showed that one reason for this pronounced effect is likely due to oxidation of reduced previously existing sulfur pools in the peat and sediment. However, it remains unresolved where the Hg in the MeHg is derived from, with likely sources from either the rainfall during the rewetting period or from liberation of previously bound mercury in sediment and peat. In FY02, we initiated a laboratory experiment to see if we could reproduce the drying and rewetting effect on mercury methylation in Everglades peat, and to provide more mechanistic information on the geochemical mechanisms. That experiment is currently ongoing and is expected to be completed by the end of FY02. It is likely follow-up experiments will be needed, given that we only used peat samples from one site, and the complexity of this phenomenon will likely need further evaluation.
The experimental approach involves: (1) collection of a series of small cores and transport to a controlled clean laboratory environment in Reston, Virginia, or St. Leonard, Maryland, (2) allowing the cores to dry completely for varying lengths of time under controlled conditions, (3) rewetting the cores with water collected from the original field sites, and is some cases spiked with stable mercury isotopes, 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 scheduled to end in September 2002.
The experiment results from each of the participating groups will be coalesced into a single database, and a series of manuscripts on the results will be drafted for publication. A follow-up experiment will be conducted in FY03 (continuing into FY04) using a larger core approach and additional sites (a high sulfur and low sulfur site in the northern Everglades). The larger cores will slow down the drying process in the lab, more closely simulate conditions in the ecosystem, and allow for larger sample sizes to ease the analysis step. Additional changes to the follow-up experiment will include shorter dry times and extended sampling times following rewet.
In FY02 we collaborated with Darren Rumbold (SFWMD) and David Evans (NOAA) to execute a preliminary examination of mercury methylation rates in Florida Bay. The extremely scant literature currently available on mercury methylation in marine sediments (one published paper) suggested very low or now methylation) had persuaded us not to prioritize the Florida Bay ecosystem previously. However, our initial evaluations indicate that in fact moderate to high levels of methylation can occur in Florida Bay sediments, and may represent a primary source of methylmercury to commercial and sport fisheries. These results are were quite surprising, giving the very high levels of sulfide (100 ppm and higher) that are known to exist in Florida Bay sediments generally, and the previously identified inhibition effect of sulfide on mercury methylation. The objective of this task will be to determine a spatially complete assay of mercury methylation rates in Florida Bay, and to ascertain how the process proceeds in such sulfidic and carbon-poor sediments.
Krabbenhoft/Orem/Aiken will conduct a synoptic sampling of Florida Bay sub-ecosystems (mud flats, embayments, tidally influenced streams, etc…) to examine the biogeochemistry of mercury methylation in Florida Bay sediments. These investigations will include a complete examination of the biogeochemistry of sulfur, dissolved organic carbon, and mercury speciation and methylation rates in Florida sediments and porewater. Sediment and porewater samples will be taken and analyzed for sulfur speciation and concentrations in sediments and sediment porewater. The same overall procedures used in the Everglades marshes will be employed in Florida Bay (with some modifications to account for the oozing sediments present there), which will allow for direct comparison of our results between these contrasting but effacing ecosystems.
Preliminary efforts done in collaboration with Rumbold and Evans in Florida Bay during FY02 will greatly aid our site selection process and interpretation. Sites will be chosen to represent the majority of the east-to-west transitioning environments present in Florida Bay, as well and the near versus off shore variations. Sampling would be conducted in collaboration with Orem and Aiken.
The Placed Based Studies program has supported the development of two major hydrologic investigations and model developments in south Florida: TIME and SICS. These efforts have lead to a greatly improved understanding of the hydrologic transport processes (spatially and temporally) within Everglades National Park and the Water Conservation Areas. However, the investigators of these projects have not explicitly interfaced with biogeochemical investigations to extend the use of these hydrologic models or the power of marrying the geochemistry databases to the water flow information to yield mass flux rates. These types of calculations are important because the Everglades are a dynamic ecosystem and current modeling exercises to predict the future Everglades have primarily focused on static water level estimates, and have not considered dynamic properties like water and constituent mass fluxes. During FY03, we will initiate collaborations with the lead investigators of these two projects (Schffranek and Swain) to combine the strengths of the biogeochemistry and hydrologic research efforts to develop mass fluxes of nutrients, sulfur and mercury for the marshes.
Lead investigators (Krabbenhoft, Orem and Aiken) will first conduct exploratory conversations with the TIME and SICS research teams to develop a strategy for marrying the two research efforts more closely. From these discussions, we will identify any data gaps that may currently exist between these studies (e.g., diffusion rate estimates) and formalize field plans to acquire the needed information. Members from each research team will participate in assembling the necessary databases to derive the mass flux estimates.
This effort will be initiated in FY03, but will probably require additional follow up in FY04. Many of the ecosystem types where the TIME and SICS researchers are most active in Everglades National Park and near the coastal margins have not been evaluated at all by the ACME team. Therefore, some initial sampling of these environments will be necessary to support the completion of this sub task. Sampling efforts will be focused on those areas or specific locations where the TIME and SICS teams have monitoring instillations, which should expedite the mass flux calculations.
The ACME Phase I researchers necessarily had to focus their intensive, process oriented research in fewer locations due to the extremely time intensive nature of this work. Because of this, many sub ecosystem types have remained largely uninvestigated with respect to mercury contamination and bioaccumulation. One notable example is Big Cypress National Preserve, where Orem and McPherson have recently showed the existence of unnaturally high levels of nutrients and sulfate (compared to southern WCA 3 and Shark River Slough). In other sub ecosystems where the ACME team has worked, slight to modest levels of nutrient and sulfate contamination have generally co-existed with the highest levels of methylmercury, such as central WCA-3A.
Synoptic sampling efforts will be initiated in the fall/winter of FY03 to identify whether high levels of methylmercury exist in Big Cypress Preserve, and whether there are any spatial trends similar to what has been observed in other locations of the Everglades. Surface water, porewater, sediment and biological (e.g., periphyton, Gambusia, etc.) samples 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. Samples will be analyzed for total mercury, gaseous elemental mercury, and methylmercury species. Sampling efforts will be conducted in concert with Orem and Aiken to derive a complete geochemical data set to evaluate the similarities and/or differences between Big Cypress Preserve and the Conservation Areas. In the summer of FY03, a sampling trip will be conducted to make process specific measurements of methylation, demethylation, photo reduction, and gaseous mercury evasion.
Work in FY03 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. Results from FY03 will be compiled and prepared for publication in FY04. The study will be the first to explore mercury speciation, cycling and bioaccumulation in Big Cypress Preserve, and to assess if sulfur and methylmercury production is an issue of concern. Results will assist managers in assessing potential threats to the Big Cypress Preserve and the Ten Thousand Islands Area from nutrient and sulfur inputs.
1. 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. In total, we will have over 60 mesocosm at site 3A15 involved in our research, and in essence each mesocosm is the equivalent of a sampling site. 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 our 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. In addition, we will conduct a diel sampling study of a least 4 mesocosms (a control, g+sulfate, Hg+DOC, and Hg+sulfate+DOC) in which scientists remain on site for approximately 30-36 hours and sampling each mesocosm approximately every three hours. After the initial doses, subsequent sulfate dosing is scheduled for days 14, 28, 42, 63, 78, 91, and 105. 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 water, suspended particulates 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 pa
(2) Developing a predictive model for methylation and sulfur cycling
Methodology - Our studies suggest that there are three main, manageable, controls on MeHg production in the STAs: antecedent soil chemistry, inflowing water chemistry, and interior water level maintenance. Since MeHg production is substantially dependant on the amount and type of sulfur present in soils, and on the mercury content of soils agricultural and non-agricultural soils may have very different sulfur and mercury levels because of land-use history, although to our knowledge little information is available on soil sulfur and mercury chemistry in the STAs except for research sites in ENR and STA 2 Cell 1. Inflowing water contains three critical constituents that strongly relate to methylmercury formation, transport and bioaccumulation: sulfate, organic carbon and Hg. In addition, these constiutents may change the character of soils in the long run. Last, the timing and duration of flow-through of water of the STAs (i.e., (hydroperiod) can dramatically affect MeHg production through the initiation of drying/rewetting cycles that have been shown to dramatically increase MeHg in Everglades soil. 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. The proposed study has several linked components: (1) Survey of soil geochemistry, Hg and MeHg in STA soils; (2) Follow up examination of soil geochemistry, Hg and MeHg at ACME Everglades sites; (3) Examination of the influence of drying and wetting cycles across a wider range of soil types.
STA soil geochemistry - The Survey of soil geochemistry in STA’s is an examination of STA soil geochemistry, especially sulfur, iron, and Hg/MeHg content. This component consists primarily of a field survey of soil geochemistry 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 roduction 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.
(3) Sulfur Biogeochemistry and Toxicity Experiments
Our hypothesis is 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. To test this hypothesis, 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.
(4) Mass Balance Studies of Methylmercury in Tidal Marshes of Shark River Slough The goal of this work element is to collaborate with coastal zone researchers in the USGS (Eduardo Patino) to make use of the ongoing data gathering, sampling and instrumentation to determine if tides do serve to “pump” methylmercury from coastal environments to the oceans. To initiate this research, we will conduct a sampling effort at an instrumented (gauge height, flow rate and direction, pH, salinity, DO, and temperature) over an entire tidal cycle during the summer and winter periods to construct mass flux estimates for tidal creeks in Shark River Slough. Samples will be taken at hourly intervals over the 8-12 hour tidal cycle. Samples will include surface water, suspended particulates, and porewater, which will be analyzed for total mercury, methylmercury, sulfate, sulfide, DOC, chloride, and major cations.
U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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