This research is relevant because of the high natural production of organic carbon in the peat soils and wetlands, the relatively high carbon content of shallow ground water systems in the region, the interactions of organic matter with other chemical species, such as trace metals, divalent cations, mercury, and anthropogenic compounds, the accumulation of organic carbon in corals and carbonate precipitates, and the potential changes in the quality and reactivity of DOC resulting from land use and water management practices. Proposed attempts to return the Everglades to more natural flow conditions will result in changes to the current transport of organic matter from the Everglades Agricultural Area and the northern conservation areas to Florida Bay. The results of this research are critical for the design of effective management strategies for the ecological restoration of the Everglades and for mitigating mercury contamination of game fish in South Florida.
Aiken, G. R.; Ryan, J. N.
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The abstract, tables, figures, and bibliography are available at <http://sofia.usgs.gov/publications/papers/hg_dom_binding/>
Haitzer, Markus; Ryan, Joseph N.; Aiken, George R.; Nagy, Kathlyn L.
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The abstract, figures, tables and literature cited are available at <http://sofia.usgs.gov/publications/papers/merc_peat/index.html>
Orem, W. H.; Harvey, J.. W.; Spiker, E. C.
Aiken, George R.; Ryan, Joseph N.
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Abstract, tables, figures, and literature cited are also available at <http://sofia.usgs.gov/publications/papers/bind_hg_humic/>
Jackson, Jonah M.; Mooney, Robert H.; Choi, Jungyill
accessed online as of 11/8/2010
Lerch, H. E.; Rawlik, P.
Nagy, Kathryn L.; Aiken, George A.; Ryan, Joseph N.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the ScienceDirect website by selecting the volume and issue number.
Aiken, G. A.; Ryan, J.. N.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the ScienceDirect website by selecting the volume and issue number.
Haitzer, M.; Ryan, J. N.' Nagy, K.
The abstract is available online. The full article is available via journal subscription or single article purchase.
Aiken, G. R.; Anderson, M. P.
Aiken, G. R.; Ranville, J. F.; Bauer, M.; MacCalady, D. L.
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Atkeson, T. D.; Lange, T.; Gilmour, C. C.; Pollman, C. D.; Orem, W. H.; Mendelssohn, I. A.; Frederick, P. C.; Krabbenhoft, D. P.; Aiken, G. R.; Rumbold, D. G.; Scheidt, D. J.; Kalla, P. I.
Krabbenhoft, D. P.; Orem, W. H.; Aiken, G. R.; Roden, E.
Aiken, G. R.; Krabbenhoft, D. P.; Marvin-DiPasquale, M.; Swarzenski, C. M.
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Wentz, D. A.; Aiken, G. R.; Krabbenhoft, D. P.
Lutz, M. A.; Brigham, M. E.; Krabbenhoft, D. P.; Aiken, G. R.; Orem, W. H.; Hall, B. D.
Scudder, B. C.; Stewart, A. R.; Bell, A. H.; Aikne, G. R.
Shanley, J. B.; Driscoll, C. T.; Aiken, G. R.; Chalmers, A. T.; Towse, J. E.
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1) Field Surveys in Everglades National Park (ENP), Big Cypress National Preserve (BCNP), and Loxahatchee National Wildlife Preserve (LOX)
Beginning in FY07, field surveys were conducted in the study areas ENP, BCNP, and LOX. The proposed field surveys were similar to surveys we conducted previously in the northern and central Everglades. Samples of surface water, pore water, sediments, and biota were collected using "clean" methods previously validated by our team in the Everglades, and now used by other researchers. Samples were analyzed for Dissolved Organic Carbon (DOC) concentration and composition, sulfur species, nutrients, and ancillary biogeochemical parameters. The work in ENP included both the freshwater areas and the coastal zone. Survey work in the freshwater area of ENP focused on how restoration is impacting DOC loads, composition, and reactivity to ENP, and how DOC impacts mercury methylation and bioaccumulation. Sampling was conducted at sites specifically selected to answer the question. Sites where canal water is discharged into ENP (sites P33 and P34) were targeted. Field surveys conducted in BCNP examined potential impacts of the planned diversion of DOC 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 DOC levels is currently entering the Preserve. The threat of DOC contaminated canal water infiltrating LOX from the new Stormwater Treatment Area (STA) STA-1E and associated drainage canals bordering LOX is also of concern, with regard to increased stimulation of MeHg production and other ecological impacts associated with the transport of reactive DOC (metals, pesticides and herbicides, controls on primary productivity). We planned field surveys here in coordination with Paul McCormick (SFWMD). McCormick has been working with LOX staff to establish sites where contaminated canal water is infiltrating the Refuge, and sites chosen for our field survey were established after consultation. We continued collaboration with Paul McCormick on water quality in LOX (WCA 1), specifically focused on DOC geochemistry in Water Conservation Area (WCA) WCA1 as it 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.
(2) 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. Of particular significance are the influences of DOC on Hg reactivity. The concentrations and composition of DOC in freshwater and marine systems are very different and coastal zones are dynamic areas for DOC cycling, consumption and alteration. 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. As this model, however, does not appear to apply to coastal marine systems, an important goal of the field studies in the coastal zone was 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 examined the key factors promoting MeHg formation in coastal areas. This task specifically focused on the processes that control DOC concentration and composition in coastal environments and the influences these processes have MeHg production in coastal environments. Field surveys were conducted using an approach similar to that used by this team in the freshwater Everglades. Surface water and pore water were collected for analysis of DOC, sulfur species, nutrients, anions, and other biogeochemical parameters by this task. Field surveys were followed by experimental work (microcosms and/or mesocosms) in later years. The project will provide Comprehensive Everglades Restoration Plan (CERP) and Greater Everglades Ecosystem Restoration (GEER) management with quantitative information for critical decisions, such as estimates of the maximum DOC, sulfur, nutrient, and mercury loads producing permissible levels of methylmercury in the ecosystem and the impacts of these contaminants.
(3) Canal Water Addition Mesocosm Studies - We used 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 was intended to validate field observations, and to provide data for the prediction of the response of the environment to future conditions. We previously used mesocosms to examine the effects of various contaminants (DOC, sulfur, phosphorus, mercury (Hg) on methlmercury (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) require additional mesocosm work. For example, the marl prairie 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 uses canal water to dose mesocosms instead of specific chemical amendments. It was anticipated that this will better simulate the actual effects of canal discharge on the ecosystem.
Mesocosms were left open to the outside environment until experiments are to be run. During experiments, mesocosms were closed off and addition of specific canal water doses were 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) was 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) were determined in surface water, pore water, and sediments over time (6-12 months). Results of mesocosm experiments l 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).
(4) Sulfur Toxicity Mesocosm Experiment - This experiment was completed in FY07, with the final sampling in December 2006, and a brief follow-up sampling in March 2007. The experiment tested 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. This task provided analytical support to investigate the role of sulfate reduction on the geochemistry of DOC, especially with regard to Hg cycling. 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, pore water, and sediments, and biological studies of macrophytes, microbial populations, and microfauna.
(5) Other: Laboratory studies designed to provide fundamental information about chemical interactions between DOC and Hg that are needed to improve Everglades Hg Cycling models will continue. This aspect of our work is providing improved binding constant data required for chemical speciation models, data on the nature and strength of interactions of DOC with HgS that control Hg solubility, data on the influence of DOC on the bioavailability of both Hg and MeHg, and data on the role of DOC in the photolytic reduction and subsequent evasion of Hg from the Everglades. In addition, analytical support and technical advice were provided to Laurel Larson (Univ of Colorado) working with Jud Harvey and Greg Noe (both USGS) to study the factors controlling formation of ridge and slough structures in the Everglades and the transport of phosphorous in the system.
1. Field Surveys in ENP, BCNP, and LOX: Collaboration will continue with Paul McCormick (SFWMD) on water quality in LOX (WCA 1), specifically focused on DOC geochemistry in WCA 1.
2. Periphyton-Based Stormwater Treatment Areas (PASTA) and STA Studies: In coordination with USACE we will conduct initial field surveys in the PASTAs (periphyton STAs) to examine mercury and DOC biogeochemistry. We will also examine the macrophyte-dominated STAs for comparison. Questions to be asked include: (a) how do the different STA approaches differ in terms of mercury chemistry and production and bioaccumulation of methylmercury, (b) how do PASTAs perform in terms of DOM removal or generation compared to the macrophyte-dominated STAs, (c) how do these two different STA systems differ in terms of DOM biogeochemistry, and nutrient remobilization from internal eutrophication effects. The proposed field surveys will be similar to surveys we have previously conducted in the northern and central Everglades, and STA 1W (formerly Everglades Nutrient Removal area (ENR)). 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 for this task are analyzed for Dissolved Organic Matter (DOM), common anions and cations.
3. Mesocosm Studies in LNWR The Loxahatchee National Wildlife Refuge (LNWR) represents one of the last vestiges of the historic soft-water Everglades. This is evidenced by the low conductivity of surface water in the marsh interior (~100 micro-siemens, mS) compared with that in the canal surrounding the Refuge (1000-1500 mS). Low conductivity waters in LNWR interior are associated with a characteristic soft-water periphyton community, wetland plant species that may also be adapted to the soft-water conditions, and lower rates of key ecosystem processes (e.g., decomposition) than in areas of the Everglades impacted by canal discharges. While it has long been known that the fringes of the LNWR are affected by high conductivity canal water, recent monitoring data indicate a trend towards increased intrusion of this water into the LNWR interior with noticeable impacts on water chemistry and sensitive biota, including the possibility of increased methylmercury production and bioaccumulation.
To address this concern, Paul McCormick established a suite of experimental plots (mesocosms) in the LNWR to examine the effects of this encroachment of contaminated canal water on the Refuge. We are cooperating with Paul and LNWR staff on this project to examine mercury, sulfur, and DOC biogeochemistry in the dosed mesocosms. The mesocosms are dosed with artificial canal water that mimics the chemical composition of the canal water surrounding the refuge. We will collect samples of surface water, pore water, sediments, and using "clean" methods. Samples are analyzed for DOM, common anions and cations.
4. Canal water monitoring: We plan to continue to monitor canal water for DOM transport and reactivity. Canals are the major conduit of water to enter the Everglades from the source in the Everglades Agricultural Area (EAA). The DOM entering the Everglades has significant impacts on the ecosystem, including acting as a major control on mercury methylation in the ecosystem, enhancing remobilization of nutrients and metals from soils (internal eutrophication), and posing a threat to macrophytes and other biota through facilitated transport of undesirable compounds (metals, pesticides) and limiting the depth of the photic zone by the absorption of light.
5. Other: Laboratory studies designed to provide fundamental information about chemical interactions between DOC and Hg that are needed to improve Everglades Hg Cycling models will continue. This aspect of our work is providing improved binding constant data required for chemical speciation models, data on the nature and strength of interactions of DOC with HgS that control Hg solubility, data on the influence of DOC on the bioavailability of both Hg and MeHg, and data on the role of DOC in the photolytic reduction and subsequent evasion of Hg from the Everglades. In addition, analytical support and technical advise are provided to Laurel Larson (Univ of Colorado) working with Jud Harvey and Greg Noe (both USGS) to study the factors controlling formation of ridge and slough structures in the Everglades and the transport of phosphorous in the system.
U.S. Department of the Interior, U.S. Geological Survey
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