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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 1, Mercury Cycling, Fate and Bioaccumulation
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 Commission). 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.
Specific Relevance to Major Unanswered Questions and Information Needs Identified: (Page numbers below refer to DOI Science Plan.)
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; page 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).
Recent and Planned Products: See Contaminant Synthesis Work Plan
Work Plan to be undertaken during the proposal year and a description of the methods and procedures: Task 1, Mercury Cycling, Fate and Bioaccumulation. To ensure comparability and interpretation of our results, the surveys will be conducted using the same sampling and analytical protocols developed under the ACME program. These include many mercury-free methods developed by the USGS and adopted world wide. The data string for water, sediment and gambusia presently available for site 3A15 (from March 1995 through December 2006) is one of the longest and most well document data trend lines for mercury and methylmercury any where in the world. The fact that the data have been all derived from the same field crews and analytical lab adds considerable reliability and interpretability of the data, and have been the central data upon which many of our conclusions regarding the relative importance of the components of the mercury axis of evil (mercury, sulfate and carbon). We believe continuity of this data string is critical to infer how the restoration will affect the biogeochemistry of the Everglades. In addition, with the passage of national laws to reduce mercury emissions by 70%, trend lines like those at site 3A15 will be critical for providing direct evidence and quantifying the environmental benefits of such laws. Surveys conducted in portions of the Everglades not well covered by the ACME project will serve to provide an initial assessment of mercury/methylmercury contamination levels. Samples will be taken during early spring (February) and summer (July), when generally the annual low and high methylmercury levels are observed, respectively. All sampling efforts will include the collection of water, sediment, and gambusia, and will be analyzed using the low-level, mercury-speciation techniques applied by the USGS, Mercury Research Lab in Middleton, Wisconsin.
A limited number of coastal mangrove areas sampled in the summer of 2006 revealed some of the highest methylmercury levels ever seen by the USGS Mercury Research Lab (25 ng/L compared to Everglades typical interior marsh levels of about 0.05 to 0.50 ng/L). As of yet, no one has conducted a systematic study of the reasons underlying the very high levels of sport fish and commercial fish in Florida Bay, but the high levels observed in this initial survey would suggest the coastal, or near coastal zone, aquatic ecosystems could be a driving factor. For this part of our work plan, we will resample the locations sampled under the 2006 survey and add additional sites to our network to determine how generally applicable the initial observations are.
During FY05 and FY06, we participated in a multi-agency sponsored effort to evaluate the possible toxicological significance of sulfate loading on indigenous plants of the Everglades. Although this experiment was specifically designed to examine sulfate cycling and toxicity, it presented a good opportunity to extend our observations to assess the sulfur-dose methylmercury-production response curve. In December 2006, a final sampling effort was conducted, and in which we sampled all 32 mesocosms plus two additional ambient control sites. Samples for sediment, water and gambusia were collected, and presently in the sample queue at the USGS Mercury Research Lab.
The mesocosm experiments conducted under ACME Phase II were very useful for testing our overall hypotheses related to the controlling influence of sulfate, carbon and mercury in the methylmercury generation process. These experiments also provided quantitative estimates of the relative importance of each of these controlling components - the first time this has been done anywhere. However, we do not know how different our results may have been if the underlying substrate (peat in all our previous experiments) vary. For example, the marl prairies of ENP are largely refractory carbon and not as useable by microbial communities such as sulfate reducing bacteria. As such, ENP settings may have a greater response to added carbon that what we observed in the peat marshes of WCA 2 and WCA 3. The same could be true for the sandy substrate regions of BCNP. As part of the Contaminant Synthesis project, we will be compiling and publishing results from the previous mesocosm experiments. During this compilation and interpretation process, we will identify any critical needs or unanswered questions that those experiments generated. In addition, results from the surveys conducted in the FY07 will be available and used in combination with the previous mesocosm experiments to design a final round of mesocosm experiment that will likely be conducted ENP, BCNP or LNWR.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:09 PM(KP)
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