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David P. Krabbenhoft; George R. Aiken
The major objectives of this project are to use an integrated biogeochemical approach to examine: (1) anthropogenic-induced changes in the water chemistry of the Everglades ecosystem, (2) biogeochemical processes within the ecosystem affecting water chemistry, and (3) the predicted impacts of restoration efforts on water chemistry. The project uses a combination of field investigations, experimental approaches (mesocosm experiments in the ecosystem, and controlled laboratory experiments), and modeling to achieve these objectives. Contaminants of concern will include nutrients, sulfur, mercury, organic compounds, and other metals. Protocols for the collection of samples and chemical analyses developed during earlier studies will be employed in these efforts. Integration of the individual tasks within the project is achieved by colocation of field sampling sites, and cooperative planning and execution of laboratory and mesocosm experiments.
Data available for this project include dissolved sulfate and solid sulfur geochemistry and surface and pore water chemistry.
Aiken, G. R.; Ryan, J. N.
The full article is available via journal subscription or single article purchase. The abstract, tables, figures, and bibliography are available at <https://sofia.usgs.gov/publications/papers/hg_dom_binding/>
Orem, W. H.; Harvey, J.. W.; Spiker, E. C.
Orem, William H.; Harvey. Judson W.; Spiker, Elliot C.
Kotra, R. K.; Holmes, C. W.; Orem, W. H.; Hageman, P. L.; Briggs, P. H.; Meier, A. L.; Brown, Z. A.
Spiker, Elliott C.; Holmes, Charles W.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the website below.
Holmes, C. W.; Kendall. C.; Lerch, H. E.; Bates, A. L.; Silva, S. R.; Boylan, A.; Corum, M.; Marot, M.; Hedgman, C.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the website below.
The first page of the article may be viewed on the www.jstor.org website
Lerch, H. E.; Rawlik, P.
Loitz, J. W.; Melisiotis, A.; Orem, W.H.
The full article is available via journal subscription or single article purchase. The abstract may be viewed on the website below.
Orem, W. H.; Simmons, K. R.; Bohlen, P. J.
Posted with permission from Springer Science and Business Media. Journal of Water, Air, & Soil Pollution, Jan 2006. © Springer 2006.
During FY02, mesocosm experiments were conducted at several sites in the Everglades to test the effects of sulfate addition (3 concentration levels), inorganic mercury (3 concentration levels), DOC (2 concentration levels), inorganic mercury plus sulfate (3 concentration levels), and inorganic mercury plus DOC. Following the additions, changes in chemical species (methylmercury and other mercury species, sulfur species, DOC, nutrients, anions, cations, Fe and Mn, redox, conductivity, pH) and microbial activity (sulfate reduction and mercury methylation rates) are determined in surface water, porewater, and sediments in the mesocosms over time (usually followed for several months following the start of the experiment).
In FY02, we conducted laboratory microcosm experiments to examine the effects of drying and rewetting of Evergladesí peats on methylmercury production, mercury geochemistry, sulfur geochemistry, and nutrients.
The experimental approach to drought/burn and rewet experiments involves: (1) collection of a series of small cores from two sites (WCA 3A-15, and STA-2), (2) drying of these cores for different times in a laboratory under controlled conditions, (3) rewetting of these cores with water collected at the two core collection sites, and (4) analysis of surface water, porewater, and sediments in the rewetted cores at intervals of time following rewetting. Analytes measured in the samples included methylmercury and other mercury species, sulfur species, nutrients, anions, cations, DOC, and sediment parameters (organic carbon, total N, total P, total S, S species). Biological parameters measured included methylmercury production and sulfate reduction rates. The initial experiment was begun in March 2002 and is scheduled to end in September 2002.
1. Mesocosm Studies Mesocosms are left open to the outside environment until experiments are to be run. During experiments, mesocosms are closed off and chemical additions are made to sets of mesocosms to test the effects of the chemical additions on methylmercury production. Each chemical addition (variable) is tested at multiple concentration levels. In some sets of mesocosms, multiple chemical species are added to examine interactive effects.
We also propose to follow-up on our previous mesocosm studies on methylmercury production. Experiments will be repeated in order to verify and expand on results from FY02. A new feature in FY03 will be the use of isotopically labeled sulfate in the chemical additions to follow changes in sulfur geochemistry and its effects on methylmercury production. Our previous mesocosm experiments were focused in the northern Everglades. In FY03 we plan to add another mesocosm site in an STA (probably STA-2). These constructed wetlands can behave as zones of low methymercury production (such as ENR), but also can produce very high levels of methylmercury (STA-2). The reasons for this are not fully understood, and mesocosm experiments in the STAís will be designed to provide managers with information on how best to operate the STAís to minimize methylmercury production. Completed 2003
2. ) Drought/Burn and Rewet Experiments We will continue to analyze samples from the first drought/rewet experiment that ended in September 2002. Results from all experiment PIís will be combined in a database, and a series of publications on the results will be written up for publication. A follow-up experiment will be conducted in FY03 (continuing into FY04) using a larger core approach at two new sites (a high sulfur and low sulfur site in the northern Everglades). The larger cores will slow down the drying process in the lab, and more closely simulate conditions in the ecosystem. Additional changes to the follow-up experiment will include shorter dry times and extended sampling times following rewet. Results will provide ecosystem managers, and CERP/GEER planners with information on how to limit the effects of drought and rewet cycles on methylmercury production. Results will be especially useful for managing STAís and northern WCA 3, areas that experience more frequent drought/rewet cycles.
3. Nutrient and Sulfur Sources in Big Cypress Surface water, groundwater, porewater, and sediment cores will be collected from sites throughout the Big Cypress Preserve. Although much of Big Cypress is a sandy soil, there are areas where peat or peaty muck is present and shallow cores and porewater can be obtained. Groundwater will be obtained from existing wells in the Preserve. Samples will be analyzed for nutrients (carbon, nitrogen, and phosphorus), sulfur species, sulfur isotopic composition, uranium, and uranium activity ratio. The uranium and uranium activity ratio is used as a tracer for phosphorus sources. Orem, Zielinski, and Simmons have used this approach successfully to examine the sources of phosphorus to the northern Everglades, and to the rivers north of Lake Okeechobee. This approach can differentiate uranium (and phosphate) originating from agriculture, groundwater, and background. Similarly, sulfur isotopes will be used to trace the sources of sulfur entering Big Cypress. Orem/Bates/Lerch previously used sulfur isotopes to trace the sources of excess sulfate entering the northern Everglades.
In FY03 work will focus on sampling at selected sites throughout the Preserve, and chemical analysis of the samples. The study area will extend from the agricultural region north of the Big Cypress Preserve to the Ten Thousand Islands Area in the south. Sites will be primarily accessed by ground vehicle, but we will also explore possible helicopter support from the Big Cypress National Preserve for accessing more remote sites. Preliminary studies completed in 2003.
4.Aquifer Storage and Recovery (ASR) Water Quality Sampling of ASR experimental sites will be done in collaboration with the ASR science team, and with other members of this project looking at mercury (Krabbenhoft) and DOC (Aiken) water quality issues related to ASR. Sulfur species will be collected using a standard sampling protocol and analytical scheme, similar to that used in our work on sulfur contamination from canal discharge. In addition to sulfur species (sulfate, sulfide, thiosulfate, sulfite, total S), we will also examine the isotopic composition of the sulfur in the ASR water. This could then potentially be used to examine the fate of sulfur released from ASR water into the ecosystem. Sulfur isotope analysis delta 34S will involve isolation of the sulfate or sulfide using a precipitation approach, and measurement of the isotopic composition of the sulfur using isotope ratio mass spectrometry. We have used this approach previously to trace the sources of sulfur entering the Everglades.
Work on sulfur in ASR water in FY03 involves collaborative sampling with Krabbenhoft, Aiken, and others at selected ASR test sites. A series of preliminary samples will examine the range of sulfur concentration and speciation in ASR water, and the isotopic composition of this water.
5.Florida Bay Mercury Methylation and Sulfur Biogeochemistry The ACME II group (Krabbenhoft/Orem/Aiken) will examine the biogeochemistry of mercury methylation in Florida Bay sediments using a multifaceted field approach. This task will concentrate on evaluating the biogeochemistry of sulfur in Florida sediments and porewater. We will examine sulfur speciation and concentrations in sediments and sediment porewater. We have previously sampled in Florida Bay (1996-2001) and are familiar with the problems of coring and porewater extraction in the carbonate ooze underlying much of the bay. We will use an analytical scheme for sulfur speciation and quantification of sulfur species that we used previously in the Everglades and Florida Bay.
FY03 Work - Preliminary coring and porewater sampling to be conducted at selected sites nearshore and offshore in Florida Bay. Sampling to be conducted in collaboration with Krabbenhoft and Aiken.
(1) Sulfur Toxicity Experiment - A major effort in FY04 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. Sulfate entering the system diffuses into anoxic sediments and is reduced to sulfide. Sulfide toxicity has been shown in several environments to negatively impact freshwater aquatic plants. Current thinking 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. 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. Sampling includes geochemical studies of surface water, porewater, and sediments, and biological studies of macrophytes and microbial populations. Collaborators include D. Krabbenhoft (USGS), C. Gilmour (Smithsonian), I. Mendelssohn (LSU), and G. Aiken (USGS).
(2) 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 DOC work (Aiken-USGS), the study provides fundamental information on the major processes controlling MeHg production in the Everglades. Mesocsoms were sampled in November 2003, March 2004, and September 2004. Results to date show that added sulfate stimulates MeHg production up to concentrations of about 15 mg/l, but depresses MeHg production above this concentration due to sulfide inhibition effects. This study is scheduled for completion in November 2004. A presentation on this work was completed in FY04.
(3) Big Cypress National Preserve (BCNP) - Analyses of samples from a preliminary water quality survey of BCNP were completed in FY04, including the first Hg and MeHg data for the Preserve. The soil MeHg levels at some sites are rather high (0.1 to 8 ng/g MeHg), but the reasons for this are presently unknown. Sulfate concentrations in surface water from within BCNP are low, but some canals external to BCNP (notably L28), have relatively high sulfate concentrations. A concern is that movement of sulfate-contaminated canal water from L28 or other canals into BCNP to enhance water levels may have the unwanted effect of stimulating MeHg production. A presentation and paper on this work will be completed in FY04.
(4) Other - (a) Collaboration with Paul McCormick (USGS) of sulfur geochemistry of WCA 1 (Loxahatchee NWR). (b) Completed yearly monitoring of canal sites in EAA and the Everglades for sulfate concentration and sulfur isotope composition; 32 samples analyzed and put into database
(1) Sulfur Toxicity Experiment - A major effort in FY05 was the continuation of a sulfur toxicity experiment in WCA 3A. This experiment tests the hypothesis that excess sulfate entering the Everglades from agricultural runoff has a significant effect on biogeochemistry, macrophyte growth, and the microbial community in the ecosystem. Sulfate entering the system diffuses into anoxic sediments and is reduced to sulfide. Sulfide toxicity has been shown in several environments to negatively impact freshwater aquatic plants. Current thinking 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. Dosing of these mesocosms with varying amounts of sulfate began in November 2003 and will continue through November 2006. Sampling of the mesocosms was conducted in November, 2004, and March and August 2005. Sampling includes geochemical studies of surface water, porewater, and sediments, and biological studies of macrophytes, microbial populations, and infauna.
(2) Mercury Methylation in Coastal Environments - Initial work is focused on a survey of coastal sites in Florida bay and the SW coast to examine the concentrations and biogeochemical processes influencing methylmercury production and bioaccumulation. In FY05, a total of 7 sites along the SW coast of Florida were sampled for surface water, pore water, and sediments. Samples were analyzed for mercury species, sulfur species, nutrients..
(3) Mercury Mesocosm Studies - This experiment begun in FY03 tested the effect of additions of sulfate, Hg, and methylmercury (MeHg) production in the Everglades. Task 1 of the project examines the sulfur, major anion, and nutrient geochemistry of the mesocosms. Mesocosms were sampled in November 2003, March 2004, and September 2004. This study was completed in FY05, and results presented at the Restoration Science Meeting held in Orlando in December 2004.
(4) Big Cypress National Preserve (BCNP)- Analyses of samples from a preliminary water quality survey (December 2003) of were completed in FY05, including the first Hg and MeHg data for the Preserve. A follow-up field survey during the wet season (August 2005) was also conducted. The soil MeHg levels at some sites are rather high (0.1 to 8 ng/g MeHg), but the reasons for this are presently unknown. Results of the first survey were presented at the Restoration Science Conference in Orlando in December 2004.
(5) Other - (a) Collaboration with Paul McCormick (USGS) of sulfur geochemistry of WCA 1 (Loxahatchee NWR). (b) Completed yearly monitoring of canal sites in EAA and the Everglades for sulfate concentration and sulfur isotope composition; 32 samples analyzed and put into database.
(1) 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. Sulfate entering the system 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 experiment will test the hypothesis that excess sulfate entering the Everglades from agricultural runoff has a significant effect on macrophytes in the ecosystem. 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.
(2) Iron/Selenium Mesocosm Experiment - This experiment begun in FY05 is testing the effect of additions of iron and selenium 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 USGS), the study provides fundamental information on the major processes controlling MeHg production in the Everglades. The initial experiment was begun with iron additions into mesocosms set up in WCA 3A in June 2005. Work is closely coordinated with Task 2 of this project (Krabbenhoft et al.). Work in FY06 will focus on analysis of samples collected in June and August 2005, and on additional sampling in FY06 (Fall, winter, and summer). This experiment provides information supporting the Comprehensive Integrated Water Quality Feasibility Study in the Landscape Science needs of the DOI Science Plan, 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). Results are incorporated into conceptual, mathematical, and risk assessment models of the Everglades ecosystem.
(3) Big Cypress National Preserve (BCNP) - Results from a preliminary water quality survey in BCNP conducted in FY04 indicate that some areas of BCNP have higher than anticipated methylmercury (MeHg) concentrations. Additional sampling was conducted in wet season (August 2005). While most of the Preserve has very low levels of sulfate, much higher concentrations are found in canals outside the Preserve, especially the L28. Restoration plans call for diverting water from the L28 into BCNP to increase water levels. Work in FY06 will include analysis of the samples collected in August 2005, and preparation of a preliminary report on the FY04 and 05 sampling in BCNP. We have proposed conducting 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. 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. 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. Initial work in FY05 will focus on field surveys, similar to our approach in the freshwater Everglades. This will be followed by experimental work in later years.
(5) Other - (a) Collaboration with Krabbenhoft and Gilmour in surveys to establish MeHg hotspots in Everglades National Park.
(b) Collaboration with 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
(c) Collaboration with Krabbenhoft and Gilmour on follow-up dry/rewet studies of MeHg production. This addresses risks to wildlife from soil-borne contaminants (sulfur, mercury, organics), through studies of the effects of dry/rewet cycles
(d) We will continue collaboration with Paul McCormick on water quality in WCA 1 (Loxahatchee NWR), 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.
(e) We will continue monitoring of canal sites for sulfate concentration and sulfur isotope composition.
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 documented data trend lines for mercury and methylmercury anywhere 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.
We have proposed to extend our findings to relatively less well studied portions of the Everglades, especially those that may receive greater amounts of canal water discharge as a result of the restoration efforts (e.g., ENP, BCNP, and LNWR). 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. Three specific areas of work will be conducted in FY07: (1) sampling surveys on the federally managed lands, particularly those that are receiving canal water discharge; (2) sampling in the newly operating periphyton/limerock STAs and previously existing cattail/peat STAs; (3) sampling of the McCormick canal water dosing mesocosms in LNWR; (4) participation on the planning and execution of the Water Quality of the Greater Everglades: Fate and Transport of Nutrients and Other Contaminants symposium at the Spring 2008 GEER conference; and, (5) continued efforts toward publication of past and current results.
Data collected for dissolved sulfate concentrations and isotopic compositions include: month and year of collection, sampling location, SO4 mg/l, SO4 meq/l, and SO4 34S/32S
Data collected for surface water and pore water include: core number, depth, pH, titration alkalinity, dissolved organic carbon, sulfide, sulfate, phosphate, ammonium, nitrate, chloride, fluoride, and bromide. Concentrations of major cations in pore water include data for sodium, potassium, calcium, magnesium, iron, strontium and silicon. Surface water values are indicated by a "0" in the depth column.
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