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projects > linking land, air and water management in the southern everglades and coastal zone to water quality and ecosystem restoration: task 2, sulfur and nutrient contamination, biogeochemical cycling, and effects
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U.S. Geological Survey Greater Everglades Science Initiative (Place-Based Studies)
Fiscal Year 2004 Project Work Plan
A. GENERAL INFORMATION:
Project Title: Integrated Biogeochemical Studies in the Everglades: Nutrients, Sulfur, and Organics
This project is an integration of individual but interrelated tasks that address environmental impacts in the South Florida ecosystem using geochemical approaches. Externally derived nutrients, mercury and sulfur are three of the most important contaminants currently affecting this ecosystem. The scientific focus of this project is to examine contaminant sources, the complex interactions of these contaminants (synergistic and antagonistic), ecosystem responses to variations in contaminant loading (time and space dimensions), and how imminent ecosystem restoration steps may affect existing contaminant pools. The Everglades restoration program is prescribing ecosystem-wide changes to some of the physical, hydrological and chemical components of this ecosystem. It remains uncertain, however, what overall effects will occur as these components react to the perturbations (especially the biological and chemical components) and toward what type of "new ecosystem" the Everglades will evolve. The approaches used will be extensions of previous field efforts by the lead investigators (Orem, Krabbenhoft, Aiken, and collaborators), whereby we will enhance our abilities to address land management and ecosystem restoration questions. New methodologies implemented in this project will include the use of environmental chambers (mesocosums), controlled laboratory microcosm experiments, and isotopic tracers to provide a more definitive means for addressing specific management questions, such as "What reductions in toxicity (methylation and bioaccumulation) would be realized if atmospheric mercury emissions were reduced by 75%?" or, "Over what time scales could we expect to see improvements to the ecosystem if nutrient and sulfur loading were reduced by implementation of agricultural best management practices (BMP's) and the storm water treatment (STA) program?" Results of these biogeochemical investigations will provide critical elements for building ecosystem models and screening-level risk assessment for contaminants in the ecosystem, and this project will be closely linked with projects addressing ecosystem modelling (Reed Harris).
Project Objectives and Strategy:
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 co-location 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. The needs of ecsosytem land and water managers to understand the sources of contamination, the ecosystem response to contamination, and the likely effects of restoration on water chemistry are the principal driving forces behind the work plan proposed in this study.
We propose to carry out work in the following areas: (1) water quality studies; (2) Field-scale and laboratory-scale experimental studies; and (3) coordinating input of geochemical results into ecosystem models and risk assessment studies being conducted by others. Our work tasks in these areas will be framed within the context of the Everglades restoration effort, and needs of ecosystem land and water managers to understand how the restoration may affect water chemistry, biology, and contaminant toxicity. The overall question we are addressing with this effort is, "Near term changes to the Everglades are certain, but what will be the ecosystem-level result of these changes and over what time scales can we expect these changes to occur?" Our previous work has answered many key questions regarding mercury, sulfur, and nutrient cycling in the Everglades, and redefined several previously existing paradigms about the general environmental chemistry of mercury. At the same time, however, our work has revealed several critical information gaps that we propose to address with this proposal.
This project is designed to meet the needs of state and federal natural resource managers who need information on environmental pollutants in the Everglades, and what can be done to mitigate problems resulting from these pollutants. Toxicity from sulfur and organic compounds are two of the newer pollutants entering the ecosystem addressed by this project. Many actions related to the Everglades Restoration project could potentially affect the expression of mercury loading in terms of its toxicity, including water levels, flushing rates, STA implementation for sulfur and nutrient reductions and the use of periphyton-based treatment cells, dissolved organic carbon releases, etc. Our field and lab experiments are designed to address many of the questions that surround how restoration plans may affect mercury toxicity. Mercury emissions reduction is an enforcement decision facing not only the State of Florida, but our Nation. Currently, we cannot say with great confidence whether the mercury levels observed in the Everglades are limited by the amount of mercury continually entering the system, or some other substrate (e.g. sulfur). Although the existing data from ACME suggest that seasonal Hg loading from the atmosphere is concomitant with higher observed methylmercury levels, there are many other co-factors that could be causing this apparent correlation. Studies proposed herein will address this critical management decision. This project will also coordinate with efforts to perform a multi-contaminant risk assessment by providing analytical and data support as needed.
Potential Impacts and Major Products:
This project addresses the major water chemistry issues currently affecting the Everglades: (1) eutrophication from excess nutrients entering the ecosystem, (2) sulfur contamination of the Everglades, sulfur toxicity, and the relation of sulfur contamination to mercury methylation, (3) mercury loading and bioaccumulation in the Everglades food web, and (4) other contaminants of concern, including organic substances and metals. Results have been used, and will continue to be used by ecosystem managers in designing restoration efforts. Study results will provide critical elements for building ecosystem models and screening-level risk assessment for the principal contaminants impacting water quality in the ecosystem (nutrients/sulfur/mercury/organics). Results.will provide CERP (3005-1;3050-1,2,3,6,7,11;3060-1;3080 3,4,8,9,10), and GEER management with quantitative information for critical decisions regarding water quality and other competing issues (e.g. hydroperiod). Experimental studies provide quantitative estimates of the maximum sulfur, nutrient, and mercury loads producing permissable levels of methylmercury in the ecosystem and impacting biota. Biogeochemical recycling studies provide information that will assist in estimating the time required for ecosystem recovery from chemical contamination.
Mesocosm studies will provide quantitative estimates of the maximum sulfur, nutrient, and mercury loads producing permissable levels of methylmercury in the ecosystem. Biogeochemical recycling studies will provide information that will assist in estimating the time required for ecosystem recovery from chemical contamination. Results on water quality studies from ASR wells, Lake Okeechobee, and the Kissimmee River Basin will assist in plans for Aquifer Storage and Recovery. Geochemical results will also be incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem. Nutrient and S studies are focused on examining the sources of these contaminants, and determining the rates of recycling and nutrient sinks in the ecosystem. Results will assist managers in determining the fate of these contaminants stored in sediments. The sediment studies will also provide managers with information relevant to the effectiveness of planned remediation methods. For example, will the STA's be effective for long-term storage of nutrients removed from agricultural runoff water? Also, what will be the effect of increased hydrologic flow from the replumbing of the canal network in the Everglades on nutrient and S loading to the ecosystem? All of the scientific efforts on Hg and S will be directly related to management questions surrounding how toxic MeHg production and bioaccumulation will be affected by the restoration efforts. Studies of S contamination relate directly to the issue of MeHg production and bioaccumulation within the ecosystem, a threat to wildlife and people in South Florida. We will continue active participation in the South Florida Mercury Science Program, and provide our findings to relevant management agencies in verbal and written formats. We will solicit direct input from relevant management agencies on the design of our mesocosm and laboratory experiments. We will continue to be closely aligned with the Everglades Mercury Model development to assure field and laboratory studies are in concert with the model construction, coding, and the predictive questions being asked of the model. We will coordinate our studies with risk assessment studies related to mercury. Finally, we intend to integrate all the information from this project into one consistent database, and be in a Management Decision Support System that will be enabled with a GIS driver (ARC View).
Major products from the study include USGS Open-File Reports, articles in peer-reviewed international scientific journals, USGS Fact Sheets, abstracts and presentations at national and international scientific meetings and at client agencies, contributions to USGS and interagency synopsis reports, databases, and the electronic posting of reports and databases on the Web (sofia.usgs.gov). Input of geochemical data into ecosystem models and risk assessment studies will also be a principal product of this project.
B. WORK PLAN
Title of Task 1: Integrated Biogeochemical Studies in the Everglades: Nutrients, Sulfur, and Organics
Task Summary and Objectives:
This project integrates a number of individual but interrelated tasks that use geochemical approaches to address contaminant and water quality issues in the South Florida ecosystem. Task 1 of this project focuses on biogeochemical processes, and the sources and cycling of nutrients, S, and organics in the ecosystem. It coordinates with other tasks to examine the complex involvement of nutrients, organics, and especially S in MeHg production and bioaccumulation. A major focus is on ecosystem responses to variations in contaminant loading (changes in external and internal loading in time and space), and how imminent ecosystem restoration may affect existing contaminant pools. Concentrations of contaminants are determined in samples of surface water, porewater, groundwater, rain water, sediments, soils, vegetation, and biota. Externally derived nutrients, mercury and S are three of the most important contaminants currently affecting this ecosystem. Rather than a shotgun approach and massive sampling effort, sites for field studies are carefully selected to answer specific management-relevent questions and for field validation of results from mesocosm/microcosm experiments and modeling studies. Major objectives of this task include: (1) determining sources of contaminants to the ecosystem, (2) providing quantitative descriptions of the biogeochemical processes controlling the cycling of these contaminants of concern, (3) describing the major sinks, speciation, and stabilities of contaminants in the ecosystem, (4) developing geochemical budgets for contaminants of concern on a regional scale, and (5) providing quantitative information on contaminants for ecosystem models and risk assessment studies conducted by others. The needs of ecosystem land and water managers to understand the sources of contamination, the ecosystem response to contamination, and the likely effects of restoration on water chemistry are the principal driving forces behind the work plan proposed in this study. Specific questions addressed by this task include:
Integration of Task 1 with other project tasks is achieved by co-location 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.
Study results will provide critical elements for building ecosystem models and screening-level risk assessment for the principal contaminants impacting water quality in the ecosystem (nutrients/sulfur/mercury/organics). Results will provide CERP (3005-1;3050-1,2,3,6,7,11;3060-1;3080-3,4,8,9,10), and GEER management with quantitative information for critical decisions regarding water quality and other competing issues (e.g. hydroperiod). Results on water quality studies from Lake Okeechobee and the Kissimmee River Basin will assist in plans for Aquifer Storage and Recovery. Mesocosm studies will provide quantitative estimates of the maximum sulfur, nutrient, and mercury loads producing permissible levels of methylmercury in the ecosystem. Biogeochemical recycling studies will provide information that will assist in estimating the time required for ecosystem recovery from chemical contamination. Geochemical results will also be incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.
Our previous studies showed that large portions of the northern Everglades are contaminated with S and nutrients (especially P). Isotope tracer studies demonstrated that both the S and P originate from canals draining the Everglades Agricultural Area (EAA), and is consistent with a source from agricultural runoff (P fertilizer, and S-containing fertilizers and soil amendments). S entering the ecosystem from contaminated canal water plays a key role in regulating the amount and distribution of toxic MeHg production, a major contaminant issue in the Everglades. Other findings from earlier studies include: (1) Taylor Slough is not a major source of nutrients to eastern Florida Bay. (2) Phosphorus and nitrogen are enriched in post-1980's sediments from Florida Bay, about the same time as the first observations of seagrass dieoff. (3) Drought and fire play a key role in remobilizing sequestered contaminants from sediments (especially S), and stimulate MeHg production in drought/fire-affected areas. Current research efforts emphasize experimental studies to amplify and expand on earlier field results. This includes the use of environmental chambers (mesocosms), and laboratory studies (microcosms) to examine the effects of changing environmental conditions (increased contaminant loading, changes in hydroperiod, drought/fire) on contaminant concentrations and methylmercury production. Our new research also includes contaminant (nutrients, S, and organics) source, loading, sequestration, and cycling studies in portions of the ecosystem not previously targeted, including Lake Okeechobee and the Kissimmee River Basin, Big Cypress National Preserve, and Shark River Slough and the southwest coast.
Work to be undertaken during the proposal year and a description of the methods and procedures:
(1) MeHg Mesocosm Experiments - The major purpose of the mercury mesocosm studies is to examine the effects (individual and synergistic) of mercury, sulfate and carbon loading on MeHg production in the Everglades. Previous work at field sites throughout the Everglades, and mesocosm experiments conducted in 2001 and 2002 has shown that these geochemical parameters are the key factors affecting MeHg production and bioaccumulation in the Everglades. However, many details of the effects of these parameters on the methylation of Hg in the Everglades remain unknown, such as refinement of specific threshold levels of each constituent. This information is directly applicable to the effective management of the Everglades, and has important implications for planners of the Everglades restoration program.
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 µg/m2; or 14.3 µg 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 µg Hg, 12 mg/l sulfate and 40 mg/l DOC. As with out 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 for . 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 - Conventional wisdom holds that changes in macrophyte distributions in the Everglades (cattail replacing sawgrass) have resulted from excess phosphorus entering the ecosystem. However, areas of the ecosystem where these changes have occurred are also heavily contaminated with S. Sulfur enters these areas as sulfate from canal discharge (the sulfate has been shown to originate in the EAA from agricultural runoff and soil oxidation). The sulfate diffuses into the anoxic sediments, and microbial sulfate reduction reduces the sulfate to sulfide. Areas contaminated with high levels of sulfate also have very high levels of sulfide in porewater. Dissolved sulfide is highly reactive, and may also be toxic to both plants and animals. It may reduce the ability of oxygen to penetrate to macrophyte roots, can react with metals to make them unavailable for plant uptake, and can impact biochemical processes of plant metabolism, such as nutrient uptake. It is also worth noting that tree islands have largely disappeared from regions of the Everglades impacted by sulfur contamination. 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 WCA 3A. 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 (STA's) -
STA's have been and continue to be constructed across the northern Everglades, primarily for the removal of phosphorus from runoff waters discharged to the Everglades. The full utilization of these STA's is an important aspect of the overall Everglades restoration plan, and achieving its goals. However, production of MeHg within certain STA's, particularly STA-2 Cell 1, have prevented full utilization of these wetlands for their intended use and bring into question their net overall benefit. Presently, flow-through operations of STA's must legally be stopped if MeHg in outflow waters exceeds that in inflow waters. This situation has occurred repeatedly in STA-2 Cell 1, both on start-up, and each subsequent year after drying and rewetting of the Cell. The SFWMD and the State of Florida seek information that would allow management of STA's to reduce or eliminate excess MeHg production events. Studies conducted by the ACME project over the past few years have shown the importance of sediment geochemistry to MeHg production, including the impacts of sulfate, sulfide and dissolved organic carbon on MeHg production during wet conditions, and the importance of drying and rewetting cycles on sulfur chemistry. Here we propose to build on that information to generate information for the management of the STA's, and form a predictive capability to optimize locating and operating these water treatment facilities to enhance the overall benefit to the Everglades.
Our studies suggest that there are three main, manageable, controls on MeHg production in the STA's: 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 STA's 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 STA's (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.
Here we propose a set of studies conducted over two years that are designed to produce a predictive model for MeHg production in the STA's. 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 STA's, it will also be useful in site selection for any future treatment areas and for planning and operation of future water reservoirs. We seek to apply our knowledge of MeHg production gained in the Everglades to the STA's, through collection of comparative soil data for the STA's, 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 STA's of different soil types, through site selection, control of hydrology, and water quality. 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 STA's. The objective of this survey is to test our Everglades-based understanding of MeHg production in the STA's. The primary drivers of MeHg within Everglades surface soils are sulfur, Hg, organic carbon and hydrologic conditions. A survey of soil conditions within the STA's will allow us to determine if the same drivers operate in STA soils, with their different land-use and hydrologic-maintenance histories. Currently operating STA's would be examined first in summer/fall 2003, then the survey would be expanded to STA's 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 STA's 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 (should we do all these matrices?). 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 (ENR103, 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 have hypothesized 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 STA-2 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 STA-2 cores for at least 6 weeks.
This study confirmed that the high MeHg concentrations observed in STA-2 Cell 3 result from in situ production in surface soils immediately following rewetting. The soil chemistry at STA-2 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 STA-2 soils were higher than the 4-year average for the ACME sites of highest MeHg production in the Everglades. The %MeHg at STA-2 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 STA's. We propose to use the same sample design used in spring 2003 to make these measurements, using high S soils from STA's that have been constructed from agricultural lands. Two additional soil types would be examined. This work would be undertaken in winter 2004/2005, using FL FY 2005 funds. 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 STA's. These data will be used by others in the development of a diagenetic MeHg production model.
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 biogeochemistry in situ at the time of collection. Cores will be collected in 7 cm PVC barrels and in 10 cm Teflon barrels. Teflon barrels will be used for cores from which water samples will be taken. Cores will be returned to the Academy of Natural Sciences Environmental Research Center (ANSERC) and held at ambient summer temperature with sunlight spectrum lighting. Some cores will be maintained wet as controls, while most cores will be allowed to dry. After drying, cores will be rewetted with water from the appropriate inflow canal, dosed with a stable mercury isotope. The soil, surface water, and pore water from the rewetted cores and the controls will be sampled at approximately 0, 7 and 49 days after rewetting. The time course was chosen based on results in experiments to date. Solid phase samples and pore water samples will be taken by sacrificing whole cores; overlying water will be sampled repeatedly from cores in Teflon barrels. Water over cores will be replaced with canal water as need to maintain volume. The soil will be analyzed for total and methyl-mercury using ICP-quadrupole mass spectrometry. Digestion or distillation of samples for total and methylmercury analysis will be as previously described by ACME. Other soil measurements will include total sulfur, acid volatile sulfide, chromium reducible sulfur, organic sulfur, organic carbon, bulk density, and moisture content using standard wet and instrumental analytical methods. The surface water and pore water will be analyzed for filtered total mercury, methylmercury, sulfate, partially reduced sulfate species, sulfide, total iron, total manganese, and dissolved organic carbon using the previously referenced methods. Temperature and dissolved oxygen will be monitored in water overlying cores.
(4) Field Studies
A number of different field studies are being conducted to examine concentrations, sources, sinks, and biogeochemical cycling of various contaminants in the ecosystem. Task 1 focuses on nutrients, sulfur, and organics.
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 propose to continue this work in FY04.
Florida Bay - The ACME II group (Krabbenhoft/Orem/Aiken) will examine the biogeochemistry of mercury methylation in Florida Bay sediments using a multifaceted field approach. Task 1 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 has 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, conducted jointly with Task 2 of this project 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.
Results from this Task will be communicated to interested parties using a number of different mediums. We will continue to publish papers in the peer-reviewed scientific literature, and to make presentations at local and international scientific meetings. Databases (sulfur database, Florida Bay database, nutrients database) will be posted on the Sofia website. This approach supplies technical information, new scientific ideas and hypotheses, conceptual models, and data to other scientists and technical/scientific resource managers. These scientific publications and presentations (see Products List) present data and ideas useful to the restoration effort in South Florida, but also useful in a more general scientific context, and applicable to contamination problems and restoration efforts beyond South Florida.
Technology transfer is also a major part of our research effort. We provide training and advice on analytical methods, equipment, and sampling techniques to many of the state and federal agencies operating in South Florida. This often includes having individuals from cooperating agencies accompany us on field sampling trips. A recent example of this is a demonstration to the South Florida Water Management District on pore water collection and redox measurements in the Everglades.
We also recognize the need to communicate ideas and results to a non-technical audience that includes non-technical/scientific resource managers, government officials, legislators (state and national), local residents, and the general public. To address this need we will use a number of approaches. We will continue to produce Fact Sheets aimed at a general audience. We have a Fact Sheet planned for FY 2003 entitled "Sulfur Contamination in the Everglades", which will explain this issue in lay terms. We make presentations, as requested, at public forums on issues related to the Everglades, as well as to federal and state officials concerned with Everglades Restoration. We have also given interviews and provided tours of field sampling trips to representatives of regional and national publications (newspapers such as the Miami Hearld, and magazines such as Audubon). Several newspaper and magazine articles have resulted.
As researchers for a non-regulatory federal agency, we recognize the need for even-handedness, and full disclosure of scientific results (following appropriate internal review) to all interested parties. Results of our research are posted on web sites available to all interested parties, and presentations are made at meetings open to all. We have also had lengthy phone and personal discussions with representatives (technical and legal) of parties on all sides of controversial issues surrounding the Everglades restoration.
C. BRIEF DESCRIPTION ON HOW PROJECT TASKS SUPPORT THE DOI AND USGS EVERGLADES RESTORATION SCIENCE PLANS
This project primarily addresses water quality goals for Everglades Restoration. This is primarily addressed in Goal 1B, Get the Water Quality Right of the USGS Science Plan for Everglades Restoration. Nutrients, sulfur, and mercury represent the major contaminants impacting water quality within the ecosystem. This project addresses sources, cycling impact, and fate of these contaminants in the Everglades. Aspects of the project addressing individual portions of the USGS Science Plan are shown in italics below:
SO1. Understand ecosystem structure and processes (physical, chemical and biological).
SO2. Determine the historical ecological setting of the Everglades.
SO3. Establish ecosystem baselines and variations for restoration targets.
SO4. Monitor ecosystem response to change.
SO5. Predict ecosystem response to anthropogenic and natural changes.
The project also addresses the following DOI Objectives for Everglades Restoration:
A. Comprehensive Integrated Water Quality Feasibility Study
What is Needed
C. Decompartmentalization of Water Conservation Area 3
What Is Needed
D. Additional Water for the Everglades National Park and Biscayne Bay Reconnaissance Study
What Is Needed
E. Risks to Fish and Wildlife from Contaminants in Stormwater Treatment Areas (STA's)
What Is Needed
H. Arthur R. Marshall Loxahatchee NWR Internal Canal Structures
What Is Needed
B. Water Quality Including Contaminants
B. 1. Water Contaminants related to CERP Projects
What Is Needed
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/projects/workplans04/int-biogeo-nso.html
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Last updated: 04 September, 2013 @ 02:08 PM(KP)
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