|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 Priority Ecosystems Science (GE PES)
Fiscal Year 2007 Study Work Plan
Study Title: 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
Overview & Objective(s): Water quality remains one of the biggest issues facing restoration of the Everglades. However, a complete understanding of all the factors (external and internal) the regulate past and present water quality in the Everglades, and even more challenging to anticipate future water quality conditions that will occur in response to the restoration effort, is a significant challenge to both scientists and resource managers. Water quality studies in the Everglades over the past 10-20 years have largely focused on the phosphorus contamination and its ecological impacts. Concerns over phosphorus contamination have resulted in one of the most expensive aspects of the Everglades Restoration program, the establishment of over 45,000 acres of storm water treatment area (STAs). Because so much attention has been focused on phosphorus in south Florida, however, in some ways water quality and phosphorus have become synonymous, and thus a complete understanding of all the potential linkages between various pollutant sources, physical and hydrologic changes resulting from the restoration, and water quality is not being realized. While we recognize that excessive phosphorus loading has deleterious effects on the Everglades, other contaminants also warrant attention so that the overall restoration goal of "... to improve the quantity, quality, timing, and distribution of clean fresh water needed to restore the South Florida Ecosystem" can be achieved. The USGS has been assessing two other important contaminants, mercury (Hg) and sulfate, which are present at concentrations sufficient to pose a threat in larger portions of the ecosystem than phosphorus. Mercury, an atmospherically transported contaminant, affects the entire ecosystem. Sulfate, on the other hand, is dominantly derived from the same contamination source as phosphorus (runoff from the EAA), but affects a larger fraction of the Everglades presently (about 30 to 60 percent) due to its greater mobility in the environment and because the STAs in their current configuration due little or nothing to abate sulfate transport to the downstream Everglades. Sulfate alone can have profound impacts on natural redox conditions in wetlands, which can stress and/or kill native vegetation. In addition, the co-contamination of the environment with Hg and sulfate has an extremely important synergistic effect on the toxicity of Hg through the conversion of inorganic Hg (form atmospheric deposition) to methylmercury (MeHg), the most toxic and bioaccumulative form of Hg. Methylmercury comprises >95% of all the Hg in predator-level species. Wildlife toxicologists are only now determining many of the important ways that MeHg may be affecting fish and wildlife, including the new observations on White Ibis from the Everglades that population level effects may be occurring through toxicity to the unborn, or through substantial hormone disruption (Dr. Peter Frederick, U. of Florida).
Mercury methylation in the environment is dominantly the result of sulfate reducing bacteria (SRB), which utilize sulfate for natural processes, but that produce MeHg as an accidental byproduct if Hg is available. Thus any actions that increase sulfate reduction (such as sulfate loading) or increase Hg availability (such as increases in Hg deposition) may serve to exacerbate Hg toxicity on ecosystems. In addition, seemingly unrelated activities like alterations to hydrologic cycles (wetting and drying periods), flushing rates, other water quality constituents (especially dissolved organic carbon [DOC], iron and pH), can have pronounced effects on Hg methylation. For example, oxidation of soils leads to conversion of organic sulfur to sulfate, and thus subsequent stimulation of sulfate reduction and methylation upon re-inundation. In addition, substantial amounts of DOC are also derived from EAA runoff and shows about the same aerial extent as sulfate. We know DOC plays an important role in facilitating Hg availability to methylating microbes, but other important processes that may be affected by DOC increases include light penetration limitation, nutrient uptake, and cycling of other exogenous metals. Lastly, another byproduct of sulfate reduction, sulfide, is deleterious to many freshwater wetland plants and infauna that are indigenous to the Everglades through oxygen deprivation and suffocation, limiting nutrient uptake, and or direct toxicity.
To this point, the USGS studies on Hg and sulfate contamination in south Florida have largely focused on the water conservation areas (WCAs). Our studies have served as a template worldwide on how to conduct studies of Hg in the environment and why wetland-rich ecosystems are areas of heightened concern for MeHg exposure. In addition, our study demonstrated for the first time, the important linkages that exist between an air derived contaminant (Hg) and another from land-based sources (sulfate). During our period of study, we have documented a substantial (>90%) decline of MeHg concentrations in water, sediment and mosquito fish at our study site in central WCA3A-15, but that our other sites in WCA2A, WCA2B, and WCA1 showed no apparent change. Our data clearly show that the MeHg declines in WCA3A are directly related to declines in sulfate concentration. Mesocosm dosing tests at this site confirm that MeHg abundance is strongly controlled by sulfate additions, without any additional Hg added. This observation poses the question whether there have been large declines in sulfur uses in the EAA, or changes in water routing internal to the Everglades. Since sulfate levels over time at our northern canal and WCA2 sites show similar or modestly lower levels of sulfate, we hypothesize that changes to water routing within the Everglades are responsible for the dramatically reduced sulfate levels at WCA3A that in turn lead to near-detection level concentrations of MeHg. If this is true, then we might expect that the sulfate-rich waters that previously flowed through our study site are now discharging elsewhere, likely south to Everglades National Park (ENP) or west to Big Cypress, where increased water delivery is a priority for the Restoration program. Indeed, evidence for steadily increasing fish Hg concentrations in the ENP over the past 5 years is available for at least one monitoring site, North Prong Creek (Ted Lange, Florida Fish and Wildlife Conservation Comission). However, since our research has focused primarily north of the ENP, we do not have contemporaneous water quality data to support or refute the conclusion that the increasing fish Hg levels are due to increasing sulfate loads due to increasing water delivery from canals to the Shark River Sough. We hypothesize that the delivery of larger volumes of water to ENP will result in a greater load of sulfate, and increases in MeHg production and bioaccumulation. The overall objective of this next phase of our research is to extend our understanding of the interactions of Hg, sulfate, DOC contamination to areas of the Everglades that are anticipated to receive increasing water delivery from sulfate rich EAA runoff or ASR waters, including: ENP (including coastal or near coastal settings), Big Cypress, and Loxahatchee National Wildlife Refuge.
This Task (Task 2 of the overall study) focuses on sulfur and nutrient biogeochemistry in the Everglades, and in concert with the other tasks also examines the complex interactions of sulfur with mercury (synergistic and antagonistic). Emphasis is placed on ecosystem responses to variations in contaminant loading (changes in external and internal loading over time and space dimensions), and how imminent ecosystem restoration may affect existing contaminant pools and their impacts on natural resources in the ecosystem. The major objectives are to determine: (1) anthropogenic-induced changes in the water chemistry of the Everglades ecosystem, (2) biogeochemical processes within the ecosystem affecting water chemistry, (3) the predicted impacts of restoration efforts on water chemistry, and (4) the impacts of contaminants on natural resources in the ecosystem. The approach used includes a combination of field surveys, contaminant monitoring at key sites, experimental studies in the ecosystem using experimental chambers (mesocosms), and laboratory experiments using microcosms. The experimental field and laboratory studies are utilized to confirm conceptual models and hypotheses developed from field surveys. 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), and 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, such as estimates of the maximum sulfur, nutrient, and mercury loads producing permissable levels of methylmercury in the ecosystem, the toxic effects of sulfur on biotic assemblages, estimates of the time required for ecosystem recovery from chemical contamination, and the effects of restoration on contaminant loads and impacts of contaminants. Results are incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.
Specific Relevance to Major Unanswered Questions and Information Needs Identified: This study supports several of the projects and overall goals listed in the DOI science plan. The DOI science plan lists three overarching restoration questions (page 9) that this study has direct relevance and provides information toward answering, including: (1) What actions will improve the quantity, timing, and distribution of clean fresh water needed to restore the South Florida ecosystem? (2) What actions will restore, protect, and manage natural resources on DOI lands in South Florida? (3) What actions will recover South Florida's threatened and endangered species? Aquifer Storage and Recovery (ASR) has substantial potential to affect water quality everywhere recovered water is released to the south Florida ecosystem, and is an area of concern in the DOI Science Plan (page 27). This study has demonstrated links between water quality characteristics of waters to be injected (sulfate, DOC, DO, and pH), the water quality characteristics of water recovered, and the water quality characteristics of water within the receiving surface and ground waters. In addition, the Comprehensive Integrated Water Quality Feasibility Study (CIWQFS; page 84) identifies degraded water bodies, types and sources of waterborne pollution, establishing load reduction targets for pollutants, and the need to improve water quality. Findings from this study will assist the DOI in providing needed information to multiagency CIWQFS Project Delivery Team in identifying the linkages between water quality targets and ecosystem restoration. The need to understand the sources, cycling and fate of critical chemical constituents like mercury, and to quantify the types and sources of pollution is stated on page 85. Linked to cycling and fate, the Science Plan cites the need for water quality performance targets (page 85) that can be used to evaluate the progress of restoration, and to identify areas in need of adaptive management. This project has shown clear linkages between water quality, land management (siting and operation of STAs; pange 86), and restoration plans, which will be critical for evaluating the overall success of the Restoration effort. Finally, the Science Plan specifically identifies the need to predict the effects of hydroperiod alterations and soil and water chemistry on the bioavailability of mercury to methylation (Page 89). This project not only discovered these hydro-cycle mercury-methylation linkages, but continues to unravel its complexities. The intent of these studies is to help land managers to make decisions that reduce the effects of hydroperiod alterations on mercury methylation.
Status and Plans: Work conducted under Phase I and Phase II of the Aquatic Cycling of Mercury in the Everglades (ACME) project has largely come to a conclusion, with the exception of the "synthesis" component of that work that is described in a separate work plan. This three year project will seek to extend our knowledge of the controlling factors of mercury toxicity in the Everglades, with specific attention to geographical areas and land use and changes related to the restoration that may affect methylmercury production and bioaccumulation. Because work under ACME was largely conducted in the WCA's, we propose to direct our current and future efforts on the federally managed lands (Big Cypress National Preserve, Loxahatchee National Wildlife Refuge, and Everglades National Park). Three areas of work will be conducted in FY07: (1) sampling surveys in interior marshes where the ACME project sporadic or no data; (2) surveys in coastal areas, particularly the southern mangroves that interface Florida Bay, which has system-wide warning for high levels of mercury in game fish; (3) completion of the sulfur toxicity mesocosm study; and, (4) planning for a final set of FY08 mesocosm experiments in regions of the Everglades where the previous mesocosm tests may not have direct transferability, such as the marl regions of ENP, and sandy regions of BCNP. Planning considerations for the FY08 mesocosm experiments would be based on the results from the previous experiments and the results of the surveys (elements 1 and 2 above).
Work to be undertaken during the proposal year and a description of the methods and procedures:
Task 2 work will be conducted in coordination with tasks 1 and 3 of this project and will include the following activities in FY 2007:
(1) Sulfur Toxicity Mesocosm Experiment - This experiment will be completed in FY07, with the final sampling in December 2006, and a brief follow-up sampling in March 2007. The experiment tests the hypothesis that excess sulfate entering the Everglades from EAA canal water has numerous impacts on the ecosystem, including: toxicological effects on native macrophytes and other organisms, internal eutrophication with enhanced recycling of nutrients and DOC, stimulation of mercury methylation, sequestration of metals in sediments as metal sulfides, and changes in the microbial community. Sulfate entering the ecosystem diffuses into anoxic sediments and is reduced to sulfide. Sulfide toxicity has been shown in several environments to negatively impact freshwater aquatic plants. The current paradigm is that excess phosphorus entering the ecosystem in agricultural runoff accounts for the change in macrophyte species (cattails displacing sawgrass) observed in WCA 2A. However, excess sulfate and subsequent buildup of sulfide in sediment porewater may also be a factor. A total of 30 mesocosms were placed in central WCA 3A in FY03; half in sawgrass and half in cattails. Monthly dosing of these mesocosms with varying amounts of sulfate began in November 2003 and continued through November 2006. Sampling included geochemical studies of surface water, porewater, and sediments, and biological studies of macrophytes, microbial populations, and microfauna. Collaborators include D. Krabbenhoft (USGS), C. Gilmour (Smithsonian), I. Mendelssohn (LSU), P. McCormick (USGS), and G. Aiken (USGS). A presentation on preliminary results from the experiment was presented at the GEER meeting in June 2006. Results from this study are also included in the 2006 South Florida Environmental Report. Probable publication in FY07. Work is closely coordinated with PES-funded studies by Krabbenhoft, Aiken, and McCormick, and with work funded by Florida DEP. This experiment provides information supporting the Comprehensive Integrated Water Quality Feasibility Study in the Landscape Science needs of the DOI Science Plan (p. 85), by examining links between water quality and ecosystem structure and function, identifying degraded parts of the ecosystem and quantifying links to contaminants (nutrients, sulfur, organics, and mercury). It also provides CERP (3005-1;3050-1,2,3,6,7,11;3060-1;3080-3,4,8,9,10), and GEER management with quantitative information on the toxic effects of sulfur on macrophytes and other biota.
(2) Field Surveys in ENP, BCNP, and LOX - Beginning in FY07, field surveys will be conducted in the study areas (ENP, BCNP, LOX). The proposed field surveys will be similar to surveys we have conducted previously in the northern and central Everglades. Samples of surface water, pore water, sediments, and biota are collected using "clean" methods previously validated by our team in the Everglades, and now used by other researchers. Samples are analyzed for sulfur species, nutrients, and ancillary biogeochemical parameters. The work in ENP will include both the freshwater areas and the coastal zone. Survey work in the freshwater area of ENP will focus on how restoration is impacting sulfur loads to ENP, and how the sulfur loads impact mercury methylation and bioaccumulation, sulfur toxicity to native flora and fauna, and internal eutrophication of the system from excess sulfate. Sampling will be conducted at sites specifically selected to answer the question. Sites where canal water is discharged into ENP (sites P33 and P34) will be targeted. Field surveys conducted in BCNP will examine potential impacts of the planned diversion of sulfate contaminated water from the L28 feeder canal. This diversion has not yet been implemented, but is likely to result in increased MeHg production in BCNP. Proposed field surveys would establish present conditions within BCNP, and examine areas where water with elevated sulfate levels is currently entering the Preserve. The threat of sulfate contaminated canal water infiltrating LOX from the new STA-1E and associated drainage canals bordering LOX is also of concern, with regard to increased sulfate loads and stimulation of MeHg production. We plan field surveys here in coordination with Paul McCormack (USGS-BRD). McCormack has been working with LOX staff to establish sites where contaminated canal water is infiltrating the Refuge, and sites chosen for our field survey would be established after consultation. The surveys provide information supporting the Comprehensive Integrated Water Quality Feasibility Study in the Landscape Science needs of the DOI Science Plan (p. 85), by examining links between water quality and ecosystem structure and function, identifying degraded parts of the ecosystem and quantifying links to contaminants (nutrients, sulfur, organics, and mercury). It also provides CERP (3005-1;3050-1,2,3,6,7,11;3060-1;3080-3,4,8,9,10), and GEER management with quantitative information on the effects of restoration on the movement of toxic substances (sulfur, mercury) into pristine parts of the ecosystem, especially protected federal lands. This work also addresses the Combined Structural and Operational Plan (CSOP) and the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement by addressing the potential for increases in toxic contaminant loads (especially sulfur) and its ecological impact, p. 71. We will continue collaboration with Paul McCormick on water quality in LOX (WCA 1), specifically focused on sulfur geochemistry and the paleoenvironmental chemical conditions in WCA 1. This supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structure Project by addressing the impacts of water quality (sulfur/nutrients/mercury) and water management practices on refuge resources, p. 40.
(3) MeHg Production in the Coastal Zone - The coastal zone of ENP and the southwest coast will receive increased freshwater flow from restoration activities, but the impacts on MeHg production and bioaccumulation are unknown. Results of research conducted by this project in the Everglades, including field surveys, mesocosm studies, and laboratory experiments have provided a working model for MeHg production and bioaccumulation in the freshwater Everglades and similar environments. This model, however, does not appear to apply to coastal marine systems. An important goal of the field studies in the coastal zone will be to determine the relative importance of MeHg flux from the freshwater Everglades, compared to in situ production of MeHg in coastal sediments. It is also unclear how the coastal system differs from the freshwater Everglades in the complex biogeochemical interactions between Hg, sulfur, and DOC in MeHg production. The proposed field studies would examine the key factors promoting MeHg formation in coastal areas. This Task will specifically focus on the role of sulfur species in MeHg production in coastal environments, and how the process differs from the freshwater environment. Work on this will be closely coordinated with activities conducted by other tasks (Krabbenhoft-Hg and Aiken-DOC). Field work will be coordinated with Eduardo Patino (USGS-WRD), who is conducting monitoring of water flux through tidal creeks in the coastal zone. His data will be important in establishing MeHg fluxes, as well as sulfur dynamics, from the increased freshwater flux accompanying restoration. Field surveys will be conducted using an approach similar to that used by this team in the freshwater Everglades. Surface water, and porewater will be collected for analysis of sulfur species, nutrients, anions, and other biogeochemical parameters by this task. Sediments will be analyzed for sulfur species, nutrient elements, and other chemical species important in regulating mercury methylation. Field surveys will be followed by experimental work )microcosms and/or mesocosms) in later years. The project 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, such as estimates of the maximum sulfur, nutrient, and mercury loads producing permissable levels of methylmercury in the ecosystem and the impacts of these contaminants. Investigations aimed at understanding MeHg production and bioaccumulation in the coastal marine environment has been identified as a principal objective of future Hg research at a recent USGS mercury Workshop for DOI scientists and land managers.
(4) Canal Water Addition Mesocosm Studies - We will use environmental chambers (~ 1 m. wide mesocosms) to examine the effects of the discharge of high ionic strength/high sulfate/high DOC canal water on the ecosystem. Anticipated impacts of contaminated canal water in the mesocosm experiments include: stimulation of methylmercury production and bioaccumulation, internal eutrophication of the system (release of nutrients and DOC from peat), and changes in the microbial, faunal, and floral assemblages. The mesocosm work is intended to validate field observations, and to provide data for the prediction of the response of the environment to future conditions. We have previously used mesocosms to examine the effects of various contaminants (sulfur, phosphorus, Hg) on MeHg production and bioaccumulation in the central Everglades (WCA's). This work provided experimental validation of the effects of Hg and sulfur loading, and DOC complexation on MeHg production and bioaccumulation in this portion of the Everglades. Different environmental conditions in the target areas for this project (ENP, BCNP) requires additional mesocosm work. For example, the marl prarie area in ENP, and the cypress swamp of BCNP are ecologically and environmentally different from the ridge and slough environment of the central WCA's. Planned mesocosm studies will examine how these environments respond to changing freshwater inputs with variable water quality characteristics, with respect to MeHg production and bioaccumulation. Another difference from our previous studies is that this experiment will use canal water to dose mesocosms instead of specific chemical amendments. It is anticipated that this will better simulate the actual effects of canal discharge on the ecosystem.
Mesocosms are left open to the outside environment until experiments are to be run. During experiments, mesocosms are closed off and addition of specific canal water doses are made to sets of mesocosms to test the effects of contaminants in the canal water on: methylmercury production and bioaccumulation, internal eutrophication, and changes in the microbial, faunal, and floral assemblages. Each canal water addition (variable) is tested at multiple concentration levels. Following the additions, changes in chemical species (MeHg and other Hg species, sulfur species, DOC, nutrients, anions, cations, Fe and Mn, redox, conductivity, pH) and microbial activity (Hg methylation) are determined in surface water, porewater, and sediments over time (6-12 months. Results of mesocosm experiments will allow prediction of how the environment in different ecotones in the Greater Everglades Ecosystem will respond to changes in water flux, and increased flux of chemical contaminants (notably sulfur). Of particular importance will be changes in MeHg production and bioaccumulation, redox conditions (from sulfide buildup in anoxic soils), and DOC and nutrient recycling (from increases in sulfate reduction rates). This experiment provides information supporting the Comprehensive Integrated Water Quality Feasibility Study in the Landscape Science needs of the DOI Science Plan (p. 85), by examining links between water quality and ecosystem structure and function, identifying degraded parts of the ecosystem and quantifying links to contaminants (nutrients, sulfur, organics, and mercury). It also provides CERP (3005-1;3050-1,2,3,6,7,11;3060-1;3080-3,4,8,9,10), and GEER management with quantitative information on the toxic effects of sulfur on macrophytes and other biota.
(1) Swarzenski P., Orem W., McPherson B., and Baskaran M. (2005) Biogeochemical transport in the Loxahatchee River estuary, Florida: The role of submarine groundwater discharge. American Geophysical Union Meeting, New Orleans, LA, May 2005, Program and Abstracts.
(2) Swarzenski P.W., Campbell P.L., Rosenbauer R., and Orem W. (2004) On the world-wide riverine transport of sediment-hosted contaminants to the ocean. AOGS, Singapore, July, 2004, Program and Abstracts.
(3) McPherson B.F., Orem W.H., and Swarzenski P.W. (2006) Assessment of ground-water input and water-quality changes impacting natural vegetation in the Loxahatchee River and floodplain ecosystem, Florida. Third Loxahatchee River Science Symposium, April 2006, Jupiter, Florida, Program and Abstracts.
(4) Orem W.H., Newman S., Gawlik D.E., Willard D., Lerch H.E., Bates A.L., and Corum M.D., 2006, Preliminary Results from Studies of Organic Biomarkers of Wading Birds: Potential for Reconstruction of Historical Trends in Wading Bird Populations. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts.
(5) Orem W.H., Wingard G.L., Holmes C.W., Lerch H.E., Bates A.L., Corum M.D., Beck M.C., and Marot M., 2006, Historical Changes in Carbon, Nitrogen, and Phosphorus in Sediments from Biscayne Bay and Florida Bay. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts.
(6) Orem W.H., Krabbenhoft D.P., Gilmour C.C., Aiken G.R., Lerch H.E., Bates A.L., and Corum M.D., 2006, Sulfur Contamination of the Everglades: Why Land and Water Managers Should be Concerned. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts.
(7) Krabbenhoft D.P., Orem W.H., Aiken G.R., and Gilmour C.C., 2006, Unraveling the Complexities of Mercury Methylation in the Everglades: The Use of Mesocosms to Test the Effects of "New" Mercury, Sulfate, and Dissolved Organic Carbon. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts.
(8) Aiken G., Krabbenhoft D.P., Orem W.H., and Gilmour C.C., 2006, Dissolved Organic Matter and Mercury in the Everglades: Implications for Ecosystem Restoration. Greater Everglades Ecosystem Restoration Meeting, Lake Buena Vista, FL, June 2006, Program and Abstracts.
(9) Swarzenski P.W., Orem W.H., McPherson B.F., Baskaran M., and Wan Y., 2006, Biogeochemical transport in the Loxahatchee River estuary, Florida - the role of submarine groundwater discharge. Third Loxahatchee River Science Symposium, April 2006, Jupiter, Florida, Program and Abstracts.
(10) Harvey J.W., McCormick P.V., and Orem W.H., 2006, Detecting pre-drainage baseline conditions of water flow, hydrologic connectivity, and water quality in the Everglades. Geological Society of America Annual Meeting, Philadelphia, PA, October 2006, Program and Abstracts.
(11) Krabbenhoft D., Gilmour C., Orem W., and Aiken G. (2006) Unraveling the Complexities of Mercury Methylation in the Everglades: The Use of Mesocosms to Test the Effects of "New" Mercury, Sulfate, and Dissolved Organic Carbon. CSA/ASCE Abstracts online.
(12) Aiken G., Krabbenhoft D., Orem W., and Gilmour C. (2007) Dissolved Organic Matter and Mercury in the Everglades: Implications for Ecosystem Restoration. Second National Conference on Ecosystem Restoration, Kansas City, April 2007, Program and Abstracts.
(13) Swarzenski P.W., Orem W.H., McPherson B.F., Baskaran M., and Wan Y., 2006, Biogeochemical transport in the Loxahatchee River estuary, Florida: The role of submarine groundwater discharge. Mar. Chem. 101: 248-265.
(14) Gilmour C., Krabbenhoft D., Orem W., Aiken G., and Roden E. (2006) Status Report on ACME Studies on the Control of Hg Methylation and Bioaccumulation in the Everglades. 2006 South Florida Environmental Report, Appendix 3B-2, South Florida Water Management District, West Palm Beach, FL, 37 pp.
(15) Krabbenhoft D., Gilmour C., Orem W., and Aiken G. (2004) Unraveling the Complexities of Mercury Methylation in the Everglades: The Use of Mesocosms to Test the Effects of "New" Mercury, Sulfate, and Dissolved Organic Carbon. Materials and Geoenvironment. 51: 1150-1151.
(16) Gilmour C., Orem W., Krabbenhoft D., Roy S., and Mendelssohn I. (2006) Preliminary assessment of sulfur sources, trends and effects in the Everglades. 2006 South Florida Environmental Report, Appendix 3B-3, South Florida Water Management District, West Palm Beach, FL, 46 pp.
(17) Zielinski R.A. , Orem W.H., Simmons K.R., and Bohlen P.J. (2006) Fertilizer-Derived Uranium and Sulfur in Rangeland Soil and Runoff: A Case Study in Central Florida. Water, Air, and Soil Poll. 176: 163-183.
(1) Orem, W.H. et al. - Synopsis Report: Sulfur Contamination in the Everglades and Sulfur Controls on Methylmercury Production, USGS Publication (July 07),
(2) Orem, W.H. et al. - Sulfate controls on mercury methylation in the central Everglades, Florida, journal publication (June 2007).
(3) Orem, W.H. et al. - Contaminant issues in Big Cypress National Preserve, Florida: mercury, sulfur and nutrients, journal publication (August 2007).
(4) Orem, W.H. et al. - Sulfate Impacts on the Everglades, Florida: Growing Concern for an Underappreciated Contaminant , National Conference on Ecosystem Restoration Meeting, Kansas City, April 2007.
U.S. Department of the Interior, U.S. Geological Survey
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