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The Aquatic Cycling of Mercury in the Everglades (ACME)

Project Proposal for 1998

Project Title: The Aquatic Cycling of Mercury in the Everglades (ACME) Project (note: this project is now part of the "Mercury Cycling in the Everglades Nutrient Removal (ENR) Areas" project)
Location of Study Area: The Florida Everglades
Project Start Date: 1/1/1995
Project End Date: 9/30/2000
Project Number: 4455-19700
Project Chief: David P. Krabbenhoft
Region/Division/Team/Section: USGS-WRD, Northeast Region
Phone: (608) 821-3843
Fax: (608) 821-3817
Mailing Address:
6417 Normandy Lane, Madison, Wisconsin, 53719
Program Element(s)/Task(s)
Element 3: Regional Mercury, Geochemistry and Water Quality Assessment. Tasks: Mercury Cycling in the Everglades (3.5), 60%; Trophic Analysis of Mercury Movement (3.6) 25%; Interactions of Mercury and DOC (3.4) 5%; Mercury Demethylation (3.3) 5%; Groundwater/surface water interactions (3.7) 5%
Collaborators, Clients:
Primary clients for this project are the resource managers responsible for making restoration recommendations for Everglades (SFWMD, FDEP, USEPA, USCOE and the National Marine Fisheries Service), and managers of the Fragile Environments Program. The SFWMD and FDEP have agreed to employ all practical means to complete the research to base restoration decisions by 12/31/1999, but that this research must be completed by 12/31/2001. These agencies must make critical decisions on very expensive restoration measures, such as the construction of nutrient removal areas and possible other mitigative plans that will exceed 1 billion dollars to implement. Other very costly, pending decisions include whether to regulate mercury emissions from waste incinerators, or to regulate agricultural practices (fertilizers and sulfur amendments). Results from the ACME project will help ecosystem managers to ascertain the efficacy of such restoration plans. Other clients include scientists conducting Hg research in similar ecosystems, who will use this research to guide and plan their activities, and the general public who frequent the Everglades and want to know more about the problem of Hg contamination in the Everglades.

The SFWMD continues to provide critical logistical support for the ACME project. On a regular basis the SFWMD provides helicopter and airboat transportation support, field personnel and gear, and access to long-term storage. The Wisconsin Department of Natural Resources (WDNR) continues to support Dr. James Hurley to spend about a third of his time on the ACME project at no cost to the USGS except to pay for travel and supplies, and the opportunity to give co-direction on research of Dr. Lisa Cleckner, a ACME project post doctoral candidate at the University of Wisconsin. The WDNR recently supported Dr. Hurley to spend 4 months at the USGS-WRD, NRP office in Boulder Colorado to facilitate the research on Hg-DOC interactions with Dr. George Aiken. USGS funds were used to pay for Dr. Hurley to drive to and from Boulder, Colorado. Finally, the WDNR also supports Dr. Paul Garrison (about 10% time) to work with the ACME scientists conducting the mercury accumulation and isotope food web studies. Both Drs. Hurley and Garrison have been invaluable contributors to the ACME project and have come at little or no added expense. Other collaborators on this effort include: USEPA, Florida Game and Freshwater Fish Commission, Benedict Estuarine Research Lab (Dr. Cindy Gilmour), all three USGS-WRD National Research Program Offices, USGS-GD, and the University of Wisconsin-Madison.


Project Summary: Mercury contamination of Everglades fish is a significant problem. The Everglades Forever Act (1994) mandates management decisions regarding what can be done to mitigate this problem. The objective of this project is to provide fundamental scientific information on the processes controlling the transport, fate and toxicity of mercury to help base restoration and mitigation plans.

Project Justification: Mercury contamination of game fish in the Everglades is of toxicological significance for fish-eating wildlife, economic significance for the citizens of south Florida who depend on sport-fishing tourism, and managerial significance for agencies responsible for making Everglades-restoration decisions. Outcomes from this effort are expected to add substantially to our understanding of the behavior and controlling processes of mercury in the Everglades, wetland ecosystems more generally, and ultimately the nation's aquatic ecosystems. Scientific findings from this project are expected to provide a primary information base for ecosystem managers who are required to make restoration decisions, and want to avoid exacerbating mercury toxicity.

Project Objectives: The overall objective of this is project is to conduct intensive, process-oriented research that focuses on tile primary mercury cycling pathways in the Everglades, and to emphasize areas that may have management implications for restoration alternatives. Five key processes control the behavior, fate, and toxicity of mercury in aquatic ecosystems: methylation, demethylation, reduction/volatilization, sedimentation/resuspension, and bio-uptake/accumulation. Tile interactions of these processes largely dictate the extent to which mercury contamination is exhibited in piscivorous organisms. However, man's activities in the south Florida ecosystem can affect the balance among these processes. Examples include: 1) overall levels and quality of DOC derived from Everglades Agricultural Area (EAA) has a controlling influence on mercury reduction1volatilization and methylmercury photoreduction rates, which are two primary detoxification mechanisms of mercury; 2) excess sulfide from the amendment of agricultural sulfur may be the primary controlling variable in mercury methylation; 3) hydroperiod length and flushing rates from pumping can dictate the overall accumulation level of methylmercury in the water column. These examples illustrate the types of research questions the ACME project is addressing within an adaptive management framework.

Overall Strategy, Study Design, and Planned Major Products: To achieve the above objectives the ACME project employs a multidisciplinary approach whereby the aquatic biogeochemical cycle and the trophic transfer routes (Figure 1) are investigated contemporaneously. We employ combined field and laboratory approaches to determine ambient conditions and process rates, respectively. Participating scientists on the AMCE project come from a variety of institutions and have expertise in microbiology, geochemistry, biology, and hydrology. Because the mercury cycle is so complex, a multidisciplinary team of investigators is necessary to unravel the complex relations among study sites. For logistical reasons, the ACME study sites were originally concentrated in the northern Everglades, but in the last year we have added ecologically differing sites in the central and southern Everglades. The ACME study was designed to quantify process rates with an ecosystem framework in mind (i.e., a connected atmosphere, hydrosphere and biosphere) so that our results would be readily usable in a Everglades mercury cycling model that could be used for management and predictive purposes. Major products produced by this effort include a Web accessible data base, yearly fact sheets summarizing progress to date, journal papers (about 3-5 per year), and a synthesis paper at the end of the project (likely a USGS professional paper).


Overall: To date, the ACME project has examined 20 sites across the Everglades: 15 marsh sites and 5 canal sites (Figure 2). These sites were chosen because they lie along existing hydraulic and nutrient gradients, where substantial ecosystem changes have occurred due to eutrophication. The effects of ecosystem eutrophication on mercury fate and toxicity is one of the largest looming questions regarding Everglades restoration (see South Florida Ecosystem Restoration: Scientific Information Needs, Science Subgroup, 9/29/94). Field trips are conducted 3-4 times per year to sample the natural variability in the wet/dry and temperature regimes. During each trip about 30-40 scientists from all the participating agencies assemble in south Florida for 10-14 days and contemporaneously conduct their specific research at each site. By bringing the participating scientists together at specific times at and a specific sites the ACME project eliminates two confounding variables (time and space) when trying to interpret and infer process information from a large and complex ecosystem.

All samples for mercury analysis (water, biota and sediment) are taken with strict adherence to ultra-clean sampling protocols. Surface and pore water samples are taken for filtered (0.4 um) Hgtotal and methylmercury (MeHg), whole-water determinations of dissolved gaseous mercury (Hg0) and reactive mercury (HgR), as well as a complete list of major cations and anions, DOC, sulfide, and other trace metals (note: unfiltered samples are also taken from surface water). Porewater samples are taken in concert with porewater pressure measurements to establish whether Groundwater discharge is a potential source of mercury. Depending on whether the water column at canal sites is stratified with respect to oxygen, 1-3 depths are sampled. All mercury samples are transported via express mail to the Mercury Research Laboratory in Madison, Wisconsin.

Due to its high reactivity, sensitivity to photochemical reactions, and low concentrations in nature, mercury concentrations are known to be temporally variable. Temporal variability assessments are being conducted on four time scales: annual, seasonal, daily, and hourly. Inter-annual and seasonal variability is addressed by conducting quarterly field trips over several years. Variability on the scale of several days is examined by incubation experiments (typically 4-5 days) to assess Hg-species stability (especially MeHg and Hg0). Short-term (hourly) variability in aqueous mercury species is determined by conducting diurnal samplings.

Most of the process rate determinations for the ACME project are accomplished through a series of incubation experiments. On a single day, sampling by helicopter is employed to gather water, sediment and biota (primarily periphyton) samples from 5 to 8 sites ecosystem wide for experimentation. Contemporaneous experiments using samples from a variety of sites enhances our ability to determine relative process rates. The experiments generally last from 1 to 5 days. From these experiments we derive rates estimates for some of the primary processes affecting mercury cycling. Incubated water samples are used to determine Hg0 production/evasion, MeHg photo degradation, and DOC photo bleaching (conducted by George Aiken). Sediment and periphyton samples are used to estimate mercury methylation and demethylation rates (conducted by Mark Marvin). More recently, we have developed a method for incubating water samples with an oxic headspace (resembling the natural environment) and monitoring mercury species shifts of all analytically determined mercury species(Hgtotal, HgR MeHg, and Hg0).

We are using isotopes of carbon (13C), nitrogen (15N) and sulfur (34S) to ascertain the origination point of MeHg into food chains, determine if the food web structure chances in the various sub-ecosystems we are studying, and to establish biomagnification factors between food-chain levels. After an initial trial of the method on Everglades samples we have derived valuable information about relative trophic positions and food web linkages that will be further detailed with subsequent field trips. Because of variable isotopic fractionations at each trophic level and overlapping compositions of sources, determinations may be problematic. Part of the problem is that we are using the bulk isotopic composition of sources to explain the bulk compositions of consumers, when only some specific compounds of the source (like fatty acids, carbohydrates, and amino acids) are actually incorporated into the consumer. A recent advance in isotope geochemistry, compound-specific isotope ratio measurement, allows the isotopic analysis of specific compounds that are consumed and incorporated into consumer tissues. We intend to employ this method to allows a more detailed analysis of food web relations.

A mercury cycling model that will incorporate Everglades specific hydrology, geochemistry, and food-web interactions will be constructed through an interagency effort by the Army Corps, SFWMD, USEPA, and USGS. This model will be used to synthesize all the information collected by this and related projects regarding the fate of mercury in the Everglades, test hypotheses, and forecast the effects of proposed restoration plans on mercury cycling. Mercury data for this project is continually undergoing a QA/QC process and being maintained (backed up daily on floppy and weekly on tape drive) on a local, PC-based database using ACCESS. Once the data has been cleared for distribution, it is uploaded to a Unix-based workstation that is using ORACLE as a database and file server for public (Internet) access. To date, a subset of the database has been uploaded to the ORACLE file server and can be accessed through the USGS, Wisconsin District Homepage.


Project Timeline for Activities on the ACME Project
(person responsible)
  1995 1996 1997 1998 1999
4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
  x x x x x x x x x x x x x x x x x      
(Olson, Dewild, Krabbenhoft)
  x x x x x x x x x x x x x x x x x x x x
  x       x       x       x       x      
(Krabbenhoft, Olson, Hurley, Cleckner)
        x x         x x     x x     x x  
x   x   x   x   x   x   x   x   x   x   x
ACME Project Deliverable Products Schedule
Product FY1995
  1995 1996 1997 1998 1999
4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Fact Sheet
              x       x       x       x  
Fact Sheet
                x       x       x       x
Archival and Web Data Bases         x x x x x x x x x x x x x x x x x
                x x     x x     x x x    
                    x       x         x x
Synthesis Paper
Synthesis Paper
                                      x x

Planned Deliverables/Products: To date, ACME scientists have published 12 abstracts at international or national scientific meeting (4th International Mercury meeting, American Chemical Society national meeting, American Society of Limnology and Oceanography national meeting), 1 Fact Sheet, and 5 manuscripts either printed or accepted and in press, and three manuscripts currently in review. It is anticipated that 3-6 abstracts, 1 Fact Sheet, and 3-5 manuscripts for scientific journal publication will continue to be produced from the ACME group on an annual basis.

Planned Outreach Activities: Primary Investigators from the ACME project are in communication on an informal basis with the three primary clients of this work on a weekly basis: South Florida Water Management District (SFWMD), Florida Department of Environmental Protection (FDEP), and the South Florida Ecosystem Program Coordinator. Once or twice annually, formal meetings are held to discuss research findings and continually reformulate the research questions in an adaptive management framework. At these meetings a much wider client base is in attendance, including the USEPA, US Army Corps of Engineers [USCOE], National Park Service, Fish and Wildlife Service, Florida Game and Freshwater Fish Commission, academia and other agencies involved in mercury research, and the private sector with interests in mercury in south Florida. Through these close and constant channels of communication, we anticipate being able to work together to meet the required report deadline of December 31, 1999 with a status report on mercury studies to the Governor of Florida and the Florida Legislator.

Prior Accomplishments in Proposed Area of Work: N/A

New Directions, Expansion of Continuing Project (if applicable): Studies done in FY98 will see an increasing emphasis on sites in the southern Everglades (WCA3 and the National Park) with more experimentation and process rate determinations, and less emphasis on site assessments. In addition, it is anticipated that SFWMD and the FDEP will have under contract an experienced modeling group to assemble a mercury cycling in the Everglades model to synthesize ACME research findings. Hypothesis testing will be conducted with this model to test various restoration plans, which could then be validated with subsequent field and laboratory studies.


Accomplishments and Outcomes, Including Outreach: The ACME project has made many findings to date, many of which have been presented at scientific meetings or included in manuscripts (see attached). Only those manuscripts originating from the Madison, Wisconsin ACME group are attached here.

  • Aqueous Hg speciation in the Northern Everglades canals and marshes reveal strong spatial and seasonal patterns.
  • Reduced flows and stagnation of waters within canals lead to increases in both MeHgU, and particle-associated MeHg.
  • Unfiltered HgT in surface water entering the marsh of WCA-2A ranged from about 1-1.5 ng L-1 while MeHgF exhibited a sixfold increase from winter to summer.
  • Transects across the marshes of WCA-2A, coupled with measurements in WCA-2B and WCA-3A reveal no apparent north to south trends in HgTU. Unfiltered MeHg, however, does appear to show enrichment at southern sites for individual sampling periods.
  • Additional analyses of HgR and DGM also suggest greater reactivity of aqueous Hg species at the southern sites.
  • The strong relationship of HgTF, and MeHgF observed in northern Wisconsin is not apparent, suggesting differences in DOC type between regions.
  • Diel studies of mercury (Hg) cycling in the Everglades revealed that dissolved gaseous mercury (DGM), total mercury (HgT), and reactive mercury (HgR) show reproducible, short-term (hourly) trends.
  • Peak water-column DGM concentrations were observed on or about noon, with a 3 to 7 fold increase over night-time concentrations.
  • Production of DGM appears to cease during dark periods, with nearly constant water column concentrations that were at or near saturation with respect to the overlying air.
  • A mass balance shows that the flux of Hg to the atmosphere from diel DGM production and evasion represents about 10% of the annual input from atmospheric deposition.
  • Diel variability in HgT and HgR appears to be controlled by two factors: inputs from rainfall and photolytic sorption/desorption processes. Methylmercury (MeHg) also showed diel trends in concentration but were not clearly linked to the solar cycle or rainfall at the study site.
  • There are discernible trends in biota Hg concentrations between sampling sites in December 1995 with an increase in Hg concentrations when moving from north to south in the study area. However, over time, the levels of MeHg and HgT in the biota can change dramatically at the same site.
  • Changes in the food web are not always related to changes in water concentrations of MeHg.
  • One factor associated with the increase in Hg in fish appears to be the percent of HgT as MeHg in the periphyton.
  • Preliminary results from the isotope food web studies show they will likely be very powerful for elucidating food web structure across this ecosystem.
  • Isotopic results clearly show that game fish in various parts of the ecosystem have different foraging habits; in some areas bass remain in canals while in others they migrate into and out of the marsh.
  • There is a consistent 6 permil shift in 15N between gambusia and periphyton across the Everglades, indicating there is likely an intermediate tropic.
  • At most sites, the 13C signature of gambusia and periphyton indicates that bulk periphyton is not the bottom of the food web, or that we need to sub-sample specific parts of the periphyton (bacterial layers) that maybe the preferred food.
  • Aqueous samples from the Florida Everglades present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg).
  • This is manifested by 1) the inability to discern when bromine monochloride (BrCl) addition is sufficient for sample oxidation for HgT analysis; and 2) incomplete spike recoveries using the distillation/ethylation technique for MeHg analysis.
  • We demonstrated a solution to this problem by ultra-violet (UV) oxidation prior to the addition of BrCl to ensure total oxidation of DOC prior to HgT analysis and copper sulfate (CuSO4) addition to aid in distillation in the presence of sulfide for MeHg analysis.

Deliverables, Products Completed:

  • Krabbenhoft, D.P., J.P. Hurley, M.L. Olson and L.B. Cleckner (1997) Diel variability of mercury phase and species distributions in the Florida Everglades. Biogeochemistry. In press.
  • Hurley, J.P., D.P. Krabbenhoft, L.B Cleckner, M.L. Olson, G. Aiken, and P.J. Rawlik (1997) System controls on aqueous mercury distribution in the northern Everglades, Biogeochemistry. In press.
  • Cleckner, L.B. P.J. Garrison, J.P. Hurley, M.L. Olson and D.P. Krabbenhoft (1997) Trophic transfer of methylmercury in the northern Everglades, Biogeochemistry.
  • Olson, M.L., L.B. Cleckner, J.P. Hurley, D.P. Krabbenhoft, and T.W. Heelan (1997) Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades, Fresenius J. Anal. Chem. In press.
  • Gilmour, C.C., G.A. Gill, M.C. Stordal and E. Spiker (1997) Mercury methylation and sulfur cycling in the Northern Everglades. Biogeochem. Inpress.
  • Mercury Studies in the Florida Everglades, Krabbenhoft, D.P. (1996) U.S. Geological Survey Fact Sheet, FS-166-96 (4 p).
  • The South Florida Mercury Science Program. (1997) Florida Department of Environmental Protection Fact Sheet. Coauthored with many.


  • Mercury transformation processes in the Everglades: temporal variations in mercury phase and species distribution and controlled exposure experiments, D.P. Krabbenhoft, J.P. Hurley, M.L. Olson, and L.B. Cleckner (Abstract) Proceedine's of the Fourth International Conference on Mercury as a Global Pollutant, August 4-8, 1996, Hamburg, Germany.
  • Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades. Olson, M.L., D.P. Krabbenhoft, L.B. Cleckner, and J.P. Hurley, (Abstract) Proceedings of the Fourth International Conference on Mercury as a Global Pollutant, August 4-8, 1996, Hamburg, Germany.
  • System controls on water column total and methyl mercury in the northern Everglades Hurley, J.P., D.P. Krabbenhoft, G. Aiken, M.L. Olson, and L.B. Cleckner, (Abstract) Proceedings of the Fourth International Conference on Mercury as a Global Pollutant, August 4-8, 1996, Hamburg, Germany.
  • Relations between water chemistry and trophic transfer of mercury in the northern Everglades, Cleckner, L.B., P.J. Garrison, J.P. Hurley, D.P. Krabbenhoft, M.L. Olson, and T. Heelen, (Abstract) Proceedings of the Fourth International Conference on Mercury as a Global Pollutant, August 4-8, 1996, Hamburg, Germany
  • King, S.A., C.J. Miles, D.P. Krabbenhoft, J.P. Hurley, and L.A. Fink, Mercury studies in the Everglades Nutrient Removal Area, Proceedings of the Fourth International Conference on Mercury as a Global Pollutant, August 4-8, 1996, Hamburg Germany.
  • Sunlight-induced, temporal variations in mercury phase and species distributions in the marshes of the Florida Everglades, David P. Krabbenhoft, J.P. Hurley, M.L. Olson, and L.B. Cleckner, (Abstract) American Chemical Society, national meeting, Program with Abstracts, Orlando, FL, August 23-28, 1996.
  • System controls on the aqueous mercury distribution in the northern Everglades, Hurley, J.P., D.P. Krabbenhoft, L.B. Cleckner, S.A. King and M.L. Olson, (Abstract) American Chemical Society, national meeting, Program with Abstracts, Orlando, FL, August 23-28, 1996.
  • Relations between water chemistry and trophic transfer of mercury in the northern Everglades, Cleckner, L.B., P.J. Garrison, J.P. Hurley, D.P. Krabbenhoft, M.L. Olson, and T. Heelen, (Abstract) American Chemical Societv, national meeting, Program with Abstracts, Orlando, FL, August 23-28, 1996.
  • The aquatic cycling of mercury in the Everglades (ACME) project: Results from the first two years of study, Krabbenhoft, D.P., J.P. Hurley, M.L. Olson, and L.B. Cleckner, (Abstract), submitted to the American Society of Limnology and Oceanography, national meeting, Santa Fe, NM, February 10- 14, 1997
  • The role of periphyton in mercury bioaccumulation in the Florida Everglades, Cleckner, L.B., J.P. Hurley and P.J. Garrison, D.P. Krabbenhoft and M.L. Olson, (Abstract), submitted to the American Society of Limnology and Oceanography, national meeting, Santa Fe, NM, February 10-14, 1996.


Required Expertise:

Required Expertise
Needs/Personnel FY1995
  1995 1996 1997 1998 1999
4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Project Coordinator
x x x x x x x x x x x x x x x x x x x x ?
Lead Lab Analyst, Lab Assist.
(Olson, Dewild, Scudder)
x x x x x x x x x x x x x   x x 50% reduced  
Post Doctoral Candidate/Food Web Specialist
        x x x x x x x x x x x x          
Mercury Research Lab.
Madison, Wisconsin
x x x x x x x x x x x x x x x x x x x x  
Web Data base assistant
(Harry House)
                x x x x x x x x x x x x  

Names of Key Project Staff:
Olson, Dewild, Scudder
Harry House

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