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
> 2001 Proposal
Project Proposal for 2001
PLACE BASED STUDIES PROGRAM
Project Title: Integrated Biogeochemical Studies in the Everglades: Nutrients and Sulfur Ecosystem: South Florida
Statement of the Problem
Previous work by this team has shown that excess nutrients and sulfur enter the Everglades from canal discharge originating in Lake Okeechobee and the Everglades Agricultural Area (Zielinski et al., 1999; Orem et al., 1999a; Bates et al., in review). The increased nutrient load has altered biotic assemblages within parts of the ecosystem, especially in areas where eutrophic-adapted cattails (Typha domingensis.) have replaced the native, oligotrophic-adapted sawgrass (Cladium jamaicense). It is also likely, though less clear, that increased nutrient load has exacerbated seagrass dieoff and extensive microalgal blooms in Florida Bay (Orem et al., 1999b). The extent of sulfur contamination in the Everglades was first documented by Bates et al. (1998) and Orem et al. (1999c). Unnaturally high levels of sulfate entering the Everglades have stimulated sulfate reduction and greatly increased concentrations of toxic and reactive hydrogen sulfide, and play a key role in controlling mercury toxicity (see below).
Mercury contamination of the Everglades ecosystem is one of the most severe cases in the published literature (Ware et al. 1990). Currently, no human consumption of any Everglades sport fish is recommended, and mercury has been identified as a principal factor in the death of at least one Florida panther which had a liver mercury concentration of 110 mg g-1 (Jordan 1990), and is strongly implicated in the deaths of two other panthers (Roelke et al. 1991). Previous work by the Aquatic Cycling of Mercury in the Everglades (ACME) project has revealed that mercury (Hg) and methylmercury (MeHg) distributions in water, sediment and biota show complex seasonal and spatial trends (Hurley et al. 1998; Cleckner et al. 1998), and that the cycling rates of Hg and MeHg are so rapid that many measurements need to be conducted on a diel basis (Krabbenhoft et al. 1998). In addition, ecosystem wide MeHg levels are controlled by in situ microbial processes (Gilmour et al. 1998; Marvin-Dipasquale and Oremland, 1998) and photochemical processes (Krabbenhoft et al. 1999a; Krabbenhoft et al. 1999b). Mercury loads to the Everglades are dominantly derived from atmospheric sources, but toxicity is largely controlled by the relative rates of conversion to methylmercury, which in turn appears to be intimately associated with the sulfate/sulfide biogeochemical cycle (Benoit et al. 1999).
- Uranium concentrations and isotopic activity ratios showed that the phosphorus contaminating portions of the northern Everglades is derived from phosphate fertilizer used in the EAA. This is the first definitive evidence that the phosphate contamination in the Everglades originates from phosphate fertilizer. A paper is currently in press in Applied Geochemistry.
- This project provided the first data showing that large parts of the northern Everglades are contaminated with sulfur. Sulfur isotope studies showed that the sulfur contamination originates from canals draining the EAA, and likely from agricultural sulfur usage in the EAA. This sulfur contamination has altered the nature of microbial processes in the freshwater marshes of the Everglades by stimulating sulfate reduction. Collaborative work with the ACME group showed that sulfur contamination in the marsh sediments is a major control on mercury methylation in the Everglades. The relationship between the biogeochemistry of methyl mercury and sulfur is complex, but the distribution of methyl mercury "hot spots" in the Everglades is largely explainable based on the sulfur geochemistry. Controls on sulfur (e.g. BMPs on agricultural sulfur usage) may be needed to help solve the mercury problem. Paper published in Chemical Geology and a second paper currently in review for J. Environmental Pollution.
- Loading of sulfur from canal discharge is just as important as external mercury loading for controlling bioaccumulation of mercury in Everglades biota.
- Recent enrichment of phosphorus and nitrogen in sediments from dated core taken in eastern and central Florida Bay was observed. This enrichment occurred beginning in the early to mid 1980s, about the same timing as the first observations of seagrass dieoff in Florida Bay, indicating a possible relationship between seagrass dieoff and nutrient enrichment. We also observed earlier periods of nutrient enrichmnet in the bay in some cores, especially a large multi-decadal event during the mid 1700s in cores from Whipray Basin with very high levels of organic carbon and nitrogen. These earlier events may be linked to changes in freshwater discharge to the bay controlled by changes in climate. These results provide information on recent changes (anthropogenic?) in nutrient input to Florida Bay, and how these recent changes fit into a historical perspective (i.e. natural cycles). Paper in press in the Journal of Coastal Research.
- Studies of nutrient accumulation and cycling in the Everglades have shown that excess phosphorus is accumulating at sites near canal discharge in WCAs 1, 2, and 3, but with WCA 2A near the Hillsboro Canal especially affected. Excess phosphorus is also accumulating near the headwaters of Taylor Slough at sites above the ENP road. We have determined that background levels of total phosphorus in surface peats of the Everglades falls in the range of 300 - 500 µg/g dry weight, similar to values we have observed in other freshwater environments such as the Okeefenokee Swamp (GA) and Dismal Swamp (VA-NC). Sites of excess phosphorus accumulation also recycle phosphorus rapidly, due to the high biodegradability of eutrophic cattail species growing at contaminated sites, compared to native oligotrophic species such as sawgrass. Because of this high rate of recycling, constructed wetland areas that consist of mostly cattail vegetation may not serve as effective long-term sinks for phosphorus. USGS Open-File Report published in 1997, and another paper in preparation.
- The first comprehensive study of tree island evolution and geochemistry was conducted. Results show that tree islands in WCA 3 first began to develop about 2,000 years ago. The tree islands and tree island tails accumulate high concentrations of sedimentary phosphorus, probably derived from the guano of nesting birds. The record of change in sedimentary phosphorus concentrations on tree islands may provide a record of natural cyclical changes in wading bird populations in the Everglades. Two papers in review for Everglades Tree Island book.
- Lignin phenols were shown to be a useful marker for research on seagrass history in Florida Bay sediments. Preliminary data from two sites in Florida Bay show evidence of natural waxing and waning of seagrass abundance within the bay. This will provide information for understanding natural fluctuations in seagrass abundance in the bay and evaluating whether recent seagrass dieoff is an unprecedented man-induced event or not. Paper in preparation.
- Extensive studies in Taylor Slough provide a baseline of information from dated cores on nutrient geochemistry, including accumulation rates for C,N,P, and S, and porewater values. Results show phosphorus contamination at the head of Taylor Slough, probably from agricultural runoff. However, this phosphorus contamination does not extend below the ENP road, and there is no evidence of significant contribution of excess phosphorus to eastern Florida Bay from discharge of Taylor Slough. A significant source of nitrogen was observed in the "White Zone" near the Taylor Slough "delta". This source appears to be from nitrogen fixation by periphyton. A source of surface water sulfate was observed near the central part of Taylor Slough paralell to the "Hole in the Donut" area. The source of this sulfate is unclear at this time. Results provide baseline information for evaluating changes resulting from the replumbing of Taylor Slough and the C-111 canal from restoration efforts. Paper in preparation.
- Based on measurements made at over a hundred sites throughout the Everglades, we conclude that the Everglades peats are dominantly anaerobic. Results also show the sediments to have a generally circumneutral pH (except for mildly acidic conditions in parts of WCA 1). Organic matter biodegradation involves primarily degradation of polysaccharrides and preservation of lignin, typical of anaerobic conditions. These redox and pH conditions are favorable for peat accumulation and mercury methylation. Paper in preparation.
- Geochemical studies of dated cores in conjunction with pollen data provides evidence for past environmental changes in the Everglades (wetter and drier periods) lasting hundreds of years, and driven primarily by climate change. For example, cores from WCA 3A show evidence of wetting and drying-out of the Everglades during climate change associated with transitions from the Medieval Warm Period to the Little Ice Age (1300-1850), to recent times. This provides a model of how the ecosystem will respond to changes in water flow associated with restoration. Paper in review in Geology.
Project Objectives and Strategy
This project is specifically designed to meet the needs of state and federal natural resource managers who need information on environmental pollutants in the Everglades, and what can be done to mitigate the problem. We will interact with resource managers on three major levels of decision making in South Florida (see figure 1). First, many actions related to the Everglades Restoration project could potentially affect the expression of mercury loading in terms of its toxicity, including water levels, flushing rates, STA implementation for sulfur and nutrient reductions and the use of periphyton-based treatment cells, DOC releases, etc We will be designing our field and lab experiments to address many of the questions that surround how restoration plans may affect mercury toxicity. Second, mercury emissions reduction is a enforcement decision facing not only the State of Florida, but our Nation. Currently, we cannot say with great confidence whether the mercury levels observed in the Everglades are limited by the amount of mercury continually entering the system, or some other substrate. Although the existing data from ACME suggest that seasonal Hg loading from the atmosphere is concomitant with higher observed methylmercury levels, there are many other co-factors that could be causing this apparent correlation. Studies proposed herein will address this critical management decision. Third, although much of the previous efforts by the PIs are directly applicable risk analyses, a thorough attempt at a multi-contaminant risk assessment has not been addressed. Tim Gross of the USGS in Gainesville, Florida has proposed to perform a mutiple-contaminant risk assessment of critical endpoints (alligators, bass, brown-bullhead, ibises, mussels and apple snails), with emphasis placed on endocrine disruption and other reproductive effects. This project will coordinate with his efforts and provide analytical and data support as funding is available.
Water Quality Task
What are the sources of contaminants of concern in the Everglades? Results of our Phase I studies showed that phosphorus and sulfur contamination in the northern Water Conservation Areas originates in canals draining the EAA. Phase I studies also showed that the EAA is not a major source of mercury to the ecosystem, although sulfur contamination from the EAA appears to play a major role in the methylation of mercury in the Everglades. Phase II studies will extend the results of our previous work using similar approaches (e.g. isotope geochemistry and quantitative chemical analysis of water samples). We will expand our existing database on sources of sulfur contamination from the EAA, and initiate studies of other contaminants of concern entering the northern Everglades by discharge from EAA canals. Other contaminants of concern would include organic chemicals and metals. These studies would be planned and conducted in collaboration with the risk assessment studies of the Everglades to be conducted by Gross and others beginning in FY 2000. We also propose to initiate studies of sources of contaminants of concern (especially nutrients and sulfur) in the Kissimmee River/Taylor Creek/Fisheating Creek area, which drains into Lake Okeechobee. Extensive dairy and beef cattle ranching in this region may be a significant source of nutrients and sulfur from livestock waste, but evidence for this is lacking. The use of Lake Okeechobee water in proposed aquifer storage and recovery (ASR) approaches to future water management in south Florida will require information on the quality of water entering the lake. In Phase II studies, we also propose to examine the source of excess phosphorus and sulfur observed at the head of Taylor Slough in Everglades National Park. Contaminants of concern in Taylor Slough may also enter the wetlands in discharge from canals draining agricultural and urban areas.
How effective are STAs in removing contaminants of concern? The constructed wetlands referred to as Storm Treatment Areas or STAs were primarily developed to act as sites for the removal of phosphorus from agricultural discharge. The SFWMD has conducted extensive studies on the effectiveness of the STAs in removing phosphorus from agricultural discharge water over the short-term. Much less information, however, exists on the effectiveness of the STAs in removing other contaminants of concern, especially sulfur. The effectiveness of STAs in removing other contaminants of concern in long-term storage will be a major goal of Phase II studies. We also propose to examine the long-term stability of cattail peat (cattails are likely to dominate the emergent macrophyte vegetation in STAs) in the sequestration of phosphorus. Preliminary work during Phase I studies suggests that peat derived from cattail vegetation is far less effective at long-term retention of phosphorus than sawgrass peat. Phase II studies will extend the results of Phase I studies in the Everglades Nutrient Removal Area or ENR (the prototype STA) and expand the work into newly constructed STAs.
What is the short-term and long-term fate of contaminants of concern in the Everglades? This question addresses the issue of the length of time the ecosystem will require to recover from contamination once the sources of the contaminants have been contained. Phase II studies of this question will involve both field work and field-scale and lab-scale experimental studies (see below). Contaminants entering wetland ecosystems are typically sequestered in various ways. Often, the final sink for the contaminant of concern is in the wetland sediments. Some contaminants continue to undergo some degree of recycling even after burial in sediments. For example, phosphorus is actively recycled from sediments by microbial processes. Microbial biodegradation of organic matter releases the phosphorus into porewater from which it can then reenter surface water by diffusion or advective flux. Other contaminants are also recycled by biogeochemical processes occurring in sediments. In addition to the continual recycling of contaminants by biogeochemical processes in sediments, events such as drought and fire can remobilize sequestered contaminants from sediments. Recent fires in WCA 3A appear to have released sequestered organic sulfur from sediments as sulfate, thereby stimulating new sulfate reduction within the wetland sediments. Field studies addressing this issue will examine biogeochemical recycling processes occurring under different types of natural conditions (e.g. eutrophied and pristine sites). The effects of catastrophic natural processes such as fires and drying events on contaminant recycling will also be examined. The forms of contaminants sequestered in sediments and the stabilities of these various forms to rerelease will be determined in the field.
Field and Lab Scale Experimental Studies
Implementation of Field-Scale Study Design - One of the difficulties of performing research in the Everglades is the inability to close mass balances due to the boundless nature of the ecosystem. We propose to include the use of mesocosums (about 2 meter diameter circular enclosures) at multiple locations throughout the Everglades. Several mesocosums would be emplaced at each location for replication of experiments and to allow for multiple, contemporaneous tests. Within the mesocosums we will perform chemical and hydrological manipulations to test the response of the ecosystem to various stresses. Potential manipulations include the addition of stable Hg isotopes (e.g., 196Hg, 199Hg, Me201Hg, Me204Hg) to trace and better quantify the myriad of biogeochemical pathways mercury can take in the environment, including bioaccumulation. By the use of isotopes, we can trace amendments made to the water column, sediments or periphyton and determine whether new mercury is "feeding" this problem, or whether it is a "recycling" phenomenon. Isotopes of sulfur, phosphorus and nitrogen will also be used in the mesocosums to examine uptake, primary production, and recycling processes in the marshes. In addition, specific components of naturally occurring dissolved organic carbon (DOC), such as hydrophobic acids that have strong affinity for mercury, will be isolated from areas where Hg methylation is known to be high and added to the mesocosums to assess its effect on mercury cycling. Likewise, DOC fractions from areas of known low MeHg production will be added to determine if these compounds inhibit methylation and bioaccumulation. Water levels and flushing rates can also be controlled within the mesocosums to simulate various Everglades restoration scenarios and their effects on water chemistry, nutrient and mercury cycling. To help facilitate the field enclosures and laboratory studies of the effects of sulfur loading (and possible synergy from dissolved organic matter) we propose to hire on a term basis Dr. Andrew Heyes, who is currently a member of Dr. Cindy Gilmours research team (included in Krabbenhoft budget sheet). Dr. Heyes is a biogeochemist who has microbial experience in Hg methylation studies and would serve as a link between the USGS interests in sulfur studies by Orem, organic carbon studies by Aiken, general mercury cycling and isotopic studies by Krabbenhoft, and methylation studies by Gilmour. He would be stationed at USGS Headquarters in Reston, VA, and conduct his experimental work in Orems geochemistry labs. DOC materials for experimentation will be provided by the Aiken team, and Hg isotopes and their analysis will be facilitated by the USGS mercury lab in Madison, WI.
The geochemical conditions at the sediment/water interface appear crucial to both Hg methylation (by control of the exchange of biologically reactive compounds such as sulfate), and to Hg and MeHg efflux ( by requiring that anoxia extend through this interface and up into the water column. We will employ diffusion gradients (DGT) and diffusion equilibria (DET) in thin films (Davison and Zhang, 1994) to study these conditions and exchanges at millimeter scales. This technique is currently being developed by the proposed postdoc (Dr. Andrew Heyes). Biological tests will also be implemented, such as examining bioaccumulation rates in Gambusia with and without periphyton present. Larry Fink (SFWMD) and Tom Atkeson (FDEP) have verbally expressed logistical and administrative support for the use of the field enclosures and chemical amendments. We have also consulted with T. Fontaine and S. Newman (SFWMD) on possible collaborative uses of field enclosures already operating in the Everglades. Our ability to employ the use of stable mercury isotopes as tracers will be facilitated by the purchase of an Inductively Coupled Plasma Mass Spectrometer (ICPMS) [Perkin Elmer, Elan 6100] through an FY1999 internal grant of the Wisconsin District, USGS Office at a cost of about $170,000.
Potential Impacts and Major Products
Nutrient studies are focused on using isotope methods (uranium/uranium isotopes, 15N, and 13C) to examine the sources of nutrients to the ecosystem, and on using sediment and porewater geochemical studies to determine the rates of nutrient recycling and nutrient sinks within the sediments. A nutrient sediment budget will be developed for incorporation in a nutrient model of the ecosystem. Results will assist managers in determining the fate of excess nutrients (especially phosphorus) stored in contaminated sediments (e.g. will the excess nutrients be buried, or recycled for movement further south into protected areas). The sediment studies will also provide managers with information relevant to the effectiveness of planned remediation methods. For example, will the type of sediments deposited in the STAs (e.g. mostly cattail peat) be effective for long-term storage of nutrients removed from agricultural runoff water? Also, what will be the effect of increased hydrologic flow from the "replumbing" of the canal network in the Everglades on nutrient mobility and recycling in the wetlands? How will this "replumbing" affect nutrient flow to the mangrove areas and Florida Bay? Studies of nutrient (and sulfur) geochemistry in dated cores will provide information on historical changes in the chemical conditions existing in south Florida wetlands. This will provide wetland managers with baseline information on the water chemistry goals needed to achieve "restoration" of the ecosystem. It will also provide land managers with an estimate of the range of concentrations of chemical species and environmental conditions that have affected the south Florida ecosystem in the past. Geochemical history data in combination with information from paleontologic studies of the USGS paleoecology group will also provide insights on how organisms in the south Florida ecosystem have responded to environmental change in the past, and predict how these organisms will likely respond to changes in the ecosystem resulting from restoration efforts.
Studies of sulfur contamination relate directly to the issue of methylmercury production and bioaccumulation within the ecosystem, a threat to wildlife and people in south Florida. Microbial sulfate reduction in anoxic wetland sediments is the principal mechanism for the methylation of mercury. Recent findings show that for south Florida wetlands methylmercury production and bioaccumulation is highly correlated with sulfide. Thus, sulfur geochemistry plays a central role in this methylation process. Our studies are focused on examining the sources of sulfur to the Everglades using stable isotope methods (34S and 18O of sulfate). Understanding the source of sulfate to the wetlands of south Florida may be a key to understanding why mercury methylation rates are so high in certain regions of the Everglades, and on how remediation efforts in the Everglades may impact mercury methylation rates. We are also examining the sulfur geochemistry of sediments on a regional scale, with emphasis on areas that are methyl mercury "hotspots". Apart from its role in methylation of mercury, sulfur is a contaminant of concern in the freshwater Everglades because of its reactivity and toxicity in the form of sulfide. Accumulation of sulfide in sediments of the Everglades can greatly alter redox conditions, metal speciation, and organic matter composition.
All of the scientific efforts related to mercury will be directly related to management questions surrounding how mercury toxicity will be affected by the restoration efforts. Efforts during the first phase of mercury investigations were necessarily more exploratory in nature, because there was essentially no previous information on mercury in the Everglades for the ACME project to form a starting point. With a good base of knowledge now in place, we can focus our studies on more specific management related questions such as those stated above in the Project Objectives and Strategy. We will continue to be active participants in the multi-agency South Florida Mercury Science Program, and will provide our findings to the relevant management agencies in verbal and written formats. We intend to continue the production of scientific journal papers, and USGS Fact Sheets to disseminate the description of our project and our findings. We will solicit direct input from relevant management agencies (e.g., SFWMD, FDEP, USEPA, F & WS, NPS) as to what they feel should be examined through the use of controlled field enclosures and laboratory tests. We will continue to be closely aligned with the Everglades Mercury Model development (EPA, SFWMD, and FDEP funded) to assure our field and laboratory studies are in concert with the model construction, coding, and the predictive questions being asked of the model. We will also coordinate our studies with the risk assessment studies related to mercury proposed by Gross and others. Finally, we intend to integrate all the information from this project into one consistent data base, and be in a Management Decision Support System that will be enabled with a GIS driver (ARC View).
Water Quality Task
-Continue collaboration with Rudnick and others (SFWMD) on nitrogen and phosphorus geochemistry in Florida Bay and the mangrove transition zone. We will continue to develop historical accumulation records for C, N, and P in Florida Bay sediments, building on our previous work (Orem et al., 1999) showing recent nutrification events as well as historical nutrification events which may be tied to historical changes in onshore hydroperiod controlled by climate change. We will examine biogeochemical processes controlling N and P recycling in the important mangrove fringe zone which appears to act as a nutrient accumulator area.
-Examine biogeochemical recycling of P and N from cattail and sawgrass peats. Areas dominated by cattails are accumulating and recycling nutrients very rapidly, in contrast to sawgrass peats where nutrient are accumulated and recycled much more slowly. It has been suggested that cattails degrade more quickly than sawgrass and thus release nutrients quickly. This raises questions about the long-term nutrient sequestering capacity of cattail peats, a critical question for managers since cattails appear to be the dominant macrophyte in the STAs. We will examine this issue by determining the organic structural differences between cattail and sawgrass plants and peat. We will use organic geochemical methods such as 13C nuclear magnetic resonance spectroscopy and lignin phenol analysis to define any differences. We will also conduct laboratory and field experiments to evaluate differences in organic decomposition and nutrient recycling rates between cattail and sawgrass peats.
-Study biogeochemical recycling and sinks for N, P, and S in new STAs and ENR. We will examine the major sinks for nutrients and sulfur in the STAs, and the biogeochemical recycling of these elements.
-Surface water inflows and outflows and groundwater chemical balances will be determined. This work will be closely coordinated with Jud Harvey (USGS/WRD), who will be conducting the water balance studies for the STAs.
-Detailed examination of sulfate/sulfide distributions in area 3A. Site 3A-15 is a known "hot spot" for methylmercury within the ecosystem, and much of WCA 3A is considered to be an area of intense methylmercury production. The location of this "hot spot" in the ecosystem may be largely controlled by the sulfur geochemistry, but detailed sulfur maps of this area are lacking. We will examine the distribution of sulfur in surface water, porewater, and sediments in a series of transects in WCA 3A. A detailed map of current sulfur distributions will allow prediction of the overall area of high methylmercury production within the ecosystem.
-Examine details of the reaction of sulfide with organic matter in Everglades peat. Organic sulfur represents the major sink of sulfur within the ecosystem. An understanding of the major forms of organic sulfur within the peat will provide information on the stability of this form of sulfur to environmental change, especially drought and fire.
Field-Scale and Lab-Scale Experimental Studies Task
-Examine rates of release of P, N and S from fire events. This will follow up on preliminary work conducted in FY 99 on fires in the northern part of WCA 3. We will conduct laboratory simulations of fire and rewetting events to examine remobilization of nutrients following fire or extended dry periods when peat oxidation may occur. Field studies of nutrient remobilization following fire or drying events and rewetting will be conducted in field enclosures, and in actual burned or dried natural areas as circumstances permit.
-Examine sulfur concentrations, speciation, and distribution in field-enclosure studies (coordination with mercury field-enclosure studies). The purpose of the field-enclosure work will be to examine how changes in environmental parameters accompanying the restoration effort will affect sulfur geochemistry. Field-enclosure sites will be selected to represent various types of environments in the Everglades, such as eutrophic sites, oligotrophic (background) slough/marsh sites, and marl prairies.
FY 2001 Deliverables/Products
FY 2000 Outreach
Bates, A.L., Orem, W.H., Harvey, J.W., and Spiker, E.C. (in review) Sulfate contamination in the Florida Everglades: Sources and relation to methylmercury production. Nature, in review.
Benoit, J.M., C.C. Gilmour, R. P. Mason, and A. Heyes (1999) Sulfide Controls on Mercury Speciation and Bioavailability to Methylating Bacteria in Sediment and Pore Waters, Environ. Sci. Technol., 33, pp. 951-957.
Cleckner, L.B. P.J. Garrison, J.P. Hurley, M.L. Olson and D.P. Krabbenhoft (1998) Trophic transfer of methylmercury in the northern Everglades, Biogeochemistry, 40: pp. 347-361.
Cleckner, L.B., C.C Gilmour, J.P. Hurley, and D.P. Krabbenhoft, 1999, Mercury Methylation by Periphyton in the Florida Everglades. In press at Limnology and Oceanography.
Davison, W. and H. Zhang (1994) In Situ speciation measurements of trace components in natural waters using thin-film gels. Nature 367: 546-548.
Delfino, J.J., Rood, B.E., Andres, M.E., Celia, D.A., and Earle, M.S., (1994) Mercury spatial hetergeneity in Everglades soil cores and comparison of mercury accumulation in wetlands and associated lakes. Report to Florida Department of Environmental Protection, Contract #SP294.
Gilmour, C.C., G.S. Riedel, M.C. Ederlington, J.T. Bell, J.M. Beniot, G.A. Gill, and M.C. Stordal (1998) Methylmercury concentrations and production rates across a trophic gradient in the Northern Everglades. Biogeochemistry, 40: pp. 326-346.
Guentzel, J.L., W.M. Landing, G.A. Gill, and C.D. Pollman (1995) Atmospheric deposition of mercury in Florida: The FAMS project (1992-1994), Water Air Soil Pollut., 80: 393-402.
Hurley, J.P., D.P. Krabbenhoft, L.B Cleckner, M.L. Olson, G. Aiken, and P.J. Rawlik, (1998) System controls on aqueous mercury distribution in the northern Everglades, Biogeochemistry, 40, pp. 293-310.
Jordan, D. (1990) Mercury contamination: Another threat to the Florida panther. Endangered Species Technical Bulletin, U.S. Fish and Wildlife Service 15(2): 1-2, Washington, D.C.
Kolka, R.K., (1996) Hydrologic transport of mercury through forested watersheds. Ph.D. Thesis, University of Minnesota, St. Paul.
Kelly, C.A., Rudd, J.W.M., Bodaly, R.A., Roulet, N.P., St. Louis, V.L., Heyes, A., Moore, R.R., Schiff, S., Aravena, R., Scott, K.J., Dyck, B., Harris, R., Warner, B., and Edwards, G. (1997) Increases in fluxes of greenhouse gases and methyl mercury following flooding of an experimental reservoir. Environmental Sci. Technol., 31, 1334-1344.
Kendall, C., Chang, C.C., Dias, R.F., Steinitz, D., Wise, E.K., and Caldwell, E.A. (1999) Tracing food web relations and fish migratory habits in the Everglades with stable isotope techniques, USGS Open-File Report 99-181, U.S. Geological Survey Program on the South Florida Ecosystem, Proceedings of South Florida Restoration Science Forum, May 17-19, 1999, Boca Raton, FL, pp. xx-xx.
Kendall, C., Garrison, P., Lange, T., Simon, N.S., Krabbenhoft, D.P., Steinitz, D., and Chang, C.C. (1997a) Evaluating food chain relations using stable isotopes [abs.], in U.S. Geological Survey Program on the South Florida Ecosystem -- Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25-27, 1997: U.S. Geological Survey Open-File Report 97-385, p. 42-43.
Kendall, C., Stober, Q.J., Meyer, P., and Silva, S.R. (1997b) Spatial distributions of isotopic compositions of gambusia and periphyton at REMAP marsh sites in the Everglades [abs.], in U.S. Geological Survey Program on the South Florida Ecosystem -- Proceedings of the Technical Symposium in Ft. Lauderdale, Florida, August 25-27, 1997: U.S. Geological Survey Open-File Report 97-385, p. 44-45.
Kendall, C., Silva, S.R., Stober, Q.J., and Meyer, P. (1998) Mapping spatial variability in marsh redox conditions in the Florida Everglades using biomass stable isotopic compositions., EOS Transactions, American Geophysical Union., vol. 79, p. S88.
Kendall, C., Chang, C.C., Dias, R.F., Steinitz, D., Wise, E.K., and Caldwell, E.A. (1999) Tracing food web relations and fish migratory habits in the Everglades with stable isotope techniques, USGS Open-File Report 99-181, U.S. Geological Survey Program on the South Florida Ecosystem, Proceedings of South Florida Restoration Science Forum, May 17-19, 1999, Boca Raton, FL, pp. XX-YY.
Krabbenhoft, D.P., J.P. Hurley, M.L. Olson and L.B. Cleckner (1998) Diel variability of mercury phase and species distributions in the Florida Everglades. Biogeochemistry, 40, pp. 311-325.
Krabbenhoft, D.P., J. P. Hurley, M.L. Olson, and G.R. Aiken (1999a) Photochemical degradation of methylmercury in the Florida Everglades, manuscript in preparation for Environmental Science and Technology.
Krabbenhoft, D.P., J. P. Hurley, M.L. Olson, G.R. Aiken, and S.L. Lindberg, (1999b) Photochemical reduction and evasion of mercury in the Florida Everglades, manuscript in preparation for Environmental Science and Technology.
Marvin-DiPasquale, M. and R.S. Oremland (1998) Bacterial Methylmercury Degradation in Florida Everglades Sediment and Periphyton. Environmental Science and Technology, 32, pp. 2556-2563.
McCormick, P.V., Shuford, R.B.E., Backus, J.G., and Kennedy, W.C. (1998) Spatial and seasonal patterns of periphyton biomass and productivity in the northern Everglades, Hydrobiologia, 362, pp. 185-208.
McPherson, B.F., Hendrix, G.Y., Klein, H., and Tyus, H.M. (1976) The Environment of South Florida, A Summary Report. USGS Professional Paper 1011, 77 p.
Orem, W.H., Lerch, H.E., Zielinski, R.A., Bates, A.L., Boylan, A., and Corum, M. (1999a) Nutrient geochemistry of the south Florida wetlands ecosystem: sources, accumulation, and biogeochemical cycling. USGS Open-File Report 99-181, U.S. Geological Survey Program on the South Florida Ecosystem, Proceedings of South Florida Restoration Science Forum, May 17-19, 1999, Boca Raton, FL, pp. 80-81.
Orem, W.H., Holmes, C.W., Kendall, C., Lerch, H.E., Bates, A.L., Silva, S.R., Boylan, A., Corum, M., Marot, M., and Hedgman, C. (1999b) Geochemistry of Florida Bay sediments: nutrient history at five sites in eastern and central Florida Bay. J. Coastal Research, in press.
Orem, W.H., Bates, A.L., Lerch, H.E., Corum, M., and Boylan, A. (1999c) Sulfur contamination in the Everglades and its relation to mercury mrthylation. USGS Open-File Report 99-181, U.S. Geological Survey Program on the South Florida Ecosystem, Proceedings of South Florida Restoration Science Forum, May 17-19, 1999, Boca Raton, FL, pp. 78-79.
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