Project Work Plan

Overview & Objective(s): The objective of this project is to more clearly define the factors that control the occurrence, nature and reactivity of dissolved organic matter (DOM) in the Florida Everglades, especially with regard to the biological transformation and accumulation of mercury (Hg). Our goal is to provide fundamental information on the nature and reactivity of DOM in the Everglades and to elucidate the mechanisms and pathways by which the DOM influences the chemistry of Hg throughout the system. 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 dissolved organic carbon (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. In addition, the presence of dissolved organic matter is important in the production of drinking water, contributes to pollutant transport, and will influence ASR performance. Finally, interactions of mercury (Hg) with organic matter play important roles in controlling the reactivity, bioavailability and transport of Hg in the Everglades. We have employed a combined field/lab approach to determine factors controlling DOM transport and reactivity with Hg. In addition, in situ experiments conducted in environmental chambers are being conducted to quantify ecological response to chemical dosing (sulfate, DOM, Hg) that will be critical for predicting ecosystem response to management decisions. 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. In FY06, we plan to execute six interrelated but independent efforts (1) to conclude the sulfate, DOC, Hg dosing studies initiated previously; (2) to examine the influence of DOM interactions on potential mitigating procedures that may be implemented in critical or particularly sensitive parts of the ecosystem; (3) to support the Sulfur Toxicity mesocosm study by analyzing the influences of sulfate on DOM concentrations and reactivity; (4) to extend our examinations of the potential for exacerbated methylmercury production in Big Cypress National Preserve by providing analyses of DOM for samples collected in a synoptic filed effort in 2005; (5) to conduct limited survey of DOM in coastal marsh settings; (6) to conduct a limited synoptic survey of the Everglades in areas that are susceptible to high potential for mercury methylation.

Data and findings are published primarily in the form of journal articles that contribute to the basic understanding of how the Everglades system functions with regard to the nature and reactivity of DOM, and how the quality of the DOM controls the reactivity of Hg. 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.

Specific Relevance to Major Unanswered Questions and Information Needs Identified: (Page numbers below refer to DOI Science Plan.)

This study supports the overarching goal, as outlined in the DOI science plan, of providing management information needs as they relate to water quality issues involving DOM, mercury and sulfur biogeochemistry. Specifically, our research supports several of the projects listed in the DOI science plan (Kissimmee-Okeechobee Watershed and Everglades Agricultural Area; Arthur R. Marshall Loxahatchee NWR Internal Canal Structures; Water Preservation Areas and Seepage Management; Everglades National park, Biscayne Bay and Florida Keys; Landscape-Scale Science Needed to Support Multiple CERP Projects) by (a) identifying factors controlling the concentration and reactivity of DOM, particularly in EAA, STAs, WCA-1, WCA-2 and WCA-3. (b) determining the effects of hydroperiod, hydrology and fire on DOM, (c) defining the interactions between DOM, sulfate and mercury on the bioavailability and transport of mercury.

The study supports the Kissimmee-Okeechobee Watershed and Everglades Agricultural Area project by providing data related to the quality waters, especially with regard to DOM, that may be injected as part of ASR (pg 27) and providing data that will be useful in monitoring and assessing the effects EAA reservoirs on the natural system (p 29). The study supports the Arthur R. Marshall Loxahatchee NWR Internal Canal Structures project by studying the factors controlling water quality, especially with regard to DOM in the STAs that will ultimately deliver water to Loxahatchee NWR (p 39-40). In a similar way, the study supports Water Preservation Areas and Seepage Management projects by providing baseline water quality data for the STA's (p44). The study supports Everglades National park, Biscayne Bay and Florida Keys projects by providing the fundamental research needed to understand the linkages between geologic, hydrologic chemical and microbial processes that control the transport and fate of DOM, control DOM interactions with mercury and ultimately control the bioreactivity and bioaccumulation of mercury (p 68). In addition, the study supports the C-111 canal project (p 71) and the Additional Water for Everglades National Park and Biscayne Bay Feasibility Study (p74) by studying the factors controlling DOM generation and transport from EAA and STAs. This information assists with the need for assessments of water quality contaminants. The study supports Landscape-Scale Science Needed to Support Multiple CERP Projects by studying the influences of STAs on water quality and the generation and transport of DOM in the STAs (p85), by addressing the need to identify linkages between water quality and ecosystem structure and function (p 85) through research designed to elucidate the links between the carbon and sulfur cycles and mercury bioavailability. This research also supports the needs to understand the factors that control mercury methylation and bioaccumulation (p 89). The study also indirectly supports Research into Potential Effects of Copper on Periphyton (p 89) by better defining the reactivity of DOM with metals and has implications for addressing water quality needs in Florida Bay (p 78) and identification of Threats Associated with ASR and In-Ground Reservoirs (p 87) by providing fundamental information of the roles played by DOM in the functioning of the Everglades ecosystem.

Status:

Currently we are focusing on 5 major study elements important for future management strategies: 1.) Hg-DOM binding studies designed to define the chemistry of DOM-Hg interactions and to improve geochemical models of the system; 2.) Assessment of the effects of DOM on Hg methylation in field mesocosm studies; 3.) Determination of the interplay between the C and S cycles to control DOM generation and reactivity with Hg 4.) Determination of the impacts of wet/dry cycling of the wetlands on Hg and DOM cycling; 5.) Characterization of DOM throughout the Everglades system, including Big Cypress National Park, STAs and coastal wetlands.

Major efforts during FY05 included the following research studies:

(1) Mercury Mesocosm Studies - This experiment begun in FY03 is testing the effect of additions of sulfate, Hg, and DOC on methylmercury (MeHg) production in the Everglades. Task 1 of the project examines the sulfur, major anion, and nutrient geochemistry of the mesocosms. In conjunction with mercury studies conducted by others (Krabbenhoft-USGS and Gilmour-Smithsonian) and sulfur work (Orem-USGS), the study provides fundamental information on the major processes controlling MeHg production in the Everglades. Mesocosms were sampled in November 2003, March 2004, September 2004 and November 2004. As part of this experiment, select mesocosms were amended with reactive organic matter isolated from the northern Everglades to determine the influence of DOM on mercury methylation. Results to date show that added DOM stimulates MeHg production by increasing the amounts of dissolved Hg in mesocosms amended with DOM. The magnitude of this effect is comparable to that observed for sulfate additions. Increased sulfate in mesocosms amended with sulfate resulted in the generation of DOM, demonstrating the interplay between the S and C cycles. In addition, mesocosms were also amended with Fe in June 2005.

(2) Sulfur Toxicity Experiment - A major effort in FY05 was the initiation of a sulfur toxicity experiment in WCA 3A. This experiment will test the hypothesis that excess sulfate entering the Everglades from agricultural runoff has a significant effect on macrophytes in the ecosystem. Dosing of these mesocosms with varying amounts of sulfate began in November 2003 and will continue through November 2006. Initial sampling of the mesocosms began in November, and follow up sampling was conducted in March and September 2004 and August 2005. Sampling includes parameters important for defining geochemistry of DOM in surface water and porewaters. Collaborators include W. Orem (USGS), D. Krabbenhoft (USGS), C. Gilmour (Smithsonian), and I. Mendelssohn (LSU).

(3) Big Cypress National Preserve (BCNP) and Coastal Zone Mercury studies- Analyses of samples for DOM from a preliminary water quality survey of BCNP and a synoptic sampling of tidal marshes along the southern coast (Florida Bay) of the Everglades were completed in FY05 and another round of samples were collected in June (Coastal Zone) and August 2005 (BCNP). These analyses, provided in support of efforts to understand mercury and sulfur geochemistries in these environments, data will be integrated into the Hg and sulfur elements of the work (Krabbenhoft, Orem).

(4) Other: Samples from select sites (ENR, STA 2, WCA1, WCA2 and WCA3) were collected in June 2005 and are in the process of being analyzed. These samples are part of a long term monitoring effort to identify changes in the concentration and chemical reactivity of DOM in the Everglades. In addition, analytical support and technical advise were provided to Laurel Larson (Univ of Colorado) working with Jud Harvey and Greg Noe to study the factors controlling formation of ridge and slough structures in the Everglades and the transport of phosphorous in the system.

Recent Products:

(1) Waples, J.S., Nagy, K.L., Aiken, G.R. and Ryan, J.N., 2004, Dissolution of Cinnabar (HgS) in the Presence of Natural Organic Matter, Geochim. Cosmochin. Acta, vol. 69, pp. 1575-1588. (2) Aiken, G., 2004, Mercury and Dissolved Organic Matter in the Florida Everglades, National Conference on Ecosystem Restoration, Orlando, FL, Dec 2004, Abstract (3) Aiken, G., 2004, Carbon, Sulfur and Mercury - A Biogeochemical Axis of Evil, Keynote Address, 2004 CALFED Science Conference, Sacramento, CA October 4-6, 2004 Abstract, (4) Aiken, G., Haitzer, M., Ryan, J.N., and Nagy, K. 2003 Interactions between dissolved organic matter and mercury in the Florida Everglades, J. du Physique, vol 107, 29-32. (5) Haitzer, M., Aiken, G.R., Ryan, J.N. 2003 Binding of Mercury to Aquatic Humic Substances, Environmental Science and Technology, vol. 37, 2436-2441. (6) Aiken, G., Haitzer, M., Ryan, J.N., and Nagy, K., 2003, Interactions between dissolved organic matter and mercury in the Florida Everglades, Journal du Physique IV France, v. 107, p.29-32. (7) Aiken, G., 2003, Interactions of dissolved organic matter with mercury in the Florida Everglades, Joint Conference on the Science and Restoration of the Greater Everglades and Florida Bay Ecosystem, Palm Harbor, Florida, Apr 13-18, 2003 Abstract (8) Drexel, E.T., Haitzer, M., Ryan, J.N., Aiken, G.R., Nagy, K. 2002 Mercury Sorption to two Florida Everglades Peats: Evidence for Strong and Weak Binding and Competition by Dissolved Organic Matter Released from Peat. Environmental Science and Technology, vol. 36, 4058-4064. (9) Haitzer, M., Aiken, G.R., Ryan, J.N. 2002 Binding of Mercury to Dissolved Organic Matter, Environmental Science and Technology, vol. 36, 3564-3570. (10) Aiken, G., Haitzer, M., Ryan, J., Nagy, K., 2002, Interactions Between Dissolved Organic Matter and Mercury in the Florida Everglades, 2002 AGU Meeting, Dec. 2002, San Francisco, CA Abstract.

Planned Products:

(1) Synopsis Report: Dissolved Organic Carbon and its Reactivity with Mercury in the Florida Everglades, (2) Biogeochemistry of Dissolved Organic Matter in the Florida Everglades Paper, (3) paper on influences of hydroperiod on the geochemistry of porewaters in the Everglades, (5) Fact Sheet on the chemistry of DOM in the Everglades, (6) Joint papers (with Krabbenhoft, Orem and Gilmour) on (a) Mercury Mesocosm Studies, and (b) Dry/Rewet Studies of Sulfur Remobilization and Methylmercury Production.

WORK PLAN

Title of Task 1: Interactions of mercury with dissolved organic carbon in the Everglades
Task Funding: USGS Greater Everglades Priority Ecosystems Science (GE PES)
Task Leaders: George Aiken
Phone: 303-541-3036
FAX: 303-447-2505
Task Status (proposed or active): active
Task priority: High
Time Frame for Task 1: FY01; FY02; FY03; FY04, FY05 and FY06.
Task Personnel: Aiken, G, Gasper, J. and Butler, K.

Task Summary and Objectives:

This study addresses the major water quality issues in the greater Everglades (nutrients, sulfur, mercury, organics), by investigating the factors that control the occurrence, nature and reactivity of dissolved organic matter (DOM) in the Florida Everglades, especially with regard to the biological transformation and accumulation of mercury (Hg). Identification of the mechanisms by which Hg interacts with DOM and quantification of these interactions are critical elements for modeling Hg transport and reactivity in the Everglades. The objectives of this task are to provide binding constant data for Hg with DOM in the Everglades and to assess the reactivity and speciation of Hg in the presence of DOM and sulfide. In addition, the overall effects of DOM on Hg cycling in the Everglades are influenced by hydrology, sources of organic matter and the presence of inorganic species, such as sulfate. Our objectives in this task are to assess the effects of these factors on DOM reactivity and to ascertain the their influence on the cycling of Hg in the Everglades. Ultimately, understanding the sources, sinks, cycling, and effects of contaminants is the first step in developing mitigation or resource management strategies to minimize the impacts of these contaminants on natural resources, while balancing other restoration priorities. 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 permissible levels of methylmercury in the ecosystem, the toxic effects of sulfur on macrophytes and other biota, 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.

Work to be undertaken during the proposal year and a description of the methods and procedures:

(1) Mercury Mesocosm Experiment - This experiment (begun in FY03) is testing the effect of additions of sulfate, Hg, and DOC on methylmercury (MeHg) production in the Everglades. In conjunction with mercury studies (Krabbenhoft-USGS and Gilmour-Smithsonian) and sulfur studies (Orem-USGS), this study provides fundamental information on the major processes controlling MeHg production in the Everglades. Results to date show that added DOM stimulates MeHg production. These results are the first to directly demonstrate the ability of DOM to increase the bioavailability of mercury for methylation through strong binding interactions and interactions with HgS and have established a new paradigm for understanding DOM-Hg interactions on the reactivity of Hg in aquatic systems. This study phase of the mesocosm research was completed in November 2004. Sample analyses continue and will be completed in FY06 at which time a presentation on this work will be completed. Another phase of the mesocosm effort began in July 2005 with the addition of iron (Fe) and selenium (Se) to the mesocosms followed by sample collection in August 2005 in an effort to test the effects of these materials on the methylation of mercury. In FY06, samples collected in 2005 will be analyzed and additional sampling of the mesocosms is planned. All efforts are closely coordinated with the research of Krabbenhoft, Orem and Gilmour. These experiments 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 for critical decisions, such as estimates of the maximum sulfur, nutrient, and mercury loads producing permissible levels of methylmercury in the ecosystem. Results are incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.

(2) Sulfur Toxicity Experiment - This experiment will continue in FY06, with major sampling efforts in November 2005, and March and August 2006. The experiment tests the hypothesis that excess sulfate entering the Everglades from agricultural runoff has a toxicological impact on native macrophytes in the ecosystem. The S and C cycles are intimately connected. Our role in this experiment is to provide insight into changes in DOM associated with elevated sulfate levels in the mesocosms. 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 will continue through November 2006. Sampling includes geochemical studies of surface water, porewater, and sediments, and biological studies of macrophytes and microbial populations. Collaborators include W. Orem (USGS), D. Krabbenhoft (USGS), C. Gilmour (Smithsonian), and I. Mendelssohn (LSU). 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.

(3) Big Cypress National Preserve (BCNP) - Results from a preliminary water quality survey in BCNP conducted in FY03 and FY04 indicate that some areas of BCNP have higher than anticipated methylmercury (MeHg) concentrations. Additional samples were collected in August 2005. Restoration plans call for diverting water from the Canal L28 into BCNP to increase water levels. However, the resulting increased sulfate and DOM loads entering the Preserve in this canal water may have the unwanted effect of stimulating MeHg production and bioaccumulation here. Work in FY06 will include analysis of the samples collected in August 2005. We have proposed (BAA CESI/PES, FY07-09) to conduct further field and mesocsom studies of MeHg production in response to increased sulfate loads in BCNP, similar to studies we have already conducted in the central Everglades. Results will provide managers with information on the effects of diverting water of high sulfate concentrations into BCNP, so that costs and benefits of this planned diversion can be assessed. Coordination with studies by Orem (USGS), Krabbenhoft (USGS) and outside collaborators (BCNP and Smithsonian) is critical. 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 for critical decisions, such as estimates of the maximum sulfur, nutrient, and mercury loads producing permissible levels of methylmercury in the ecosystem, and the effects of restoration on contaminant loads and impacts of contaminants.

(4) MeHg Production in the Coastal Zone - 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. Work in FY05 included initial survey sampling at 7 sites in the SW coastal area of the greater Everglades (June 2005) to examine the mechanism by which MeHg is produced in the coastal zone of the greater Everglades. Work in FY06 will focus on analysis of the samples collected in June 2005, as well as additional survey work. Efforts will specifically focus on the role of DOM in MeHg production in coastal environments, and how the process differs from the freshwater environment. DOM in tidally influenced waters is compositionally different from DOM transported from the WCAs in the Everglades. Task 1 will specifically focus on changes in DOM composition as freshwater mixes with brackish waters of Florida Bay, the role of DOM in MeHg production in coastal environments, and how the process differs from the freshwater environment. Initial work will focus on field surveys, similar to our approach in the freshwater Everglades. This will be followed by experimental work 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 permissible 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.

(5) Other - (a) Continued collaboration with Krabbenhoft, Gilmour, and Orem on other mesocosm studies, including studies of the effects of Fe and Se additions on MeHg production. The influence of DOM on the reactivity of both constituents will be studied. This will provide information useful for developing new approaches for mitigating MeHg production in Everglades' wetlands. (b) Collaboration with Orem, Krabbenhoft and Gilmour in surveys to establish MeHg hotspots in Everglades National Park. This 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 contaminant loads, including DOM, and its ecological impact, p. 71. (c) Collaboration with Orem, Gilmour and Krabbenhoft on STA MeHg and sulfur surveys. This addresses risks to wildlife from soil-borne contaminants (sulfur, mercury, organics), through studies of the effects of dry/rewet cycles (Threats Associated with Rehydration of Agricultural Lands, p. 87; Predicting bioavailability of mercury (methylation) following inundation of dry land based on soil and water chemistry, p. 89) on methylmercury formation. (d) Collaboration with Orem, Krabbenhoft and Gilmour on follow-up dry/rewet studies of MeHg production.

Specific Task Product(s):

(1) Synopsis Report: Dissolved Organic Carbon and its Reactivity with Mercury in the Florida Everglades, (2) Biogeochemistry of Dissolved Organic Matter in the Florida Everglades Paper, (3) paper on influences of hydroperiod on the geochemistry of porewaters in the Everglades, (4) Fact Sheet on the chemistry of DOM in the Everglades, (5) Joint papers (with Krabbenhoft, Orem and Gilmour) on (a) Mercury Mesocosm Studies, and (b) Dry/Rewet Studies of Sulfur Remobilization and Methylmercury Production, (6) Journal articles on speciation of organic S in the Everglades and a critical review of methods for determining DOM-Hg binding constants.