Program: FRAGILE ENVIRONMENTS
Project Title: Mercury Cycling in the Everglades Nutrient Removal (ENR) Areas.
Location of Study Area: The wetland construction site of the ENR project.
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
E-mail:dpkrabbe@usgs.gov
Phone: 608-276-3843
Fax: 608-276-3817
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 and the Everglades Nutrient Removal (ENR) Areas (3.5), 80%; Interactions of Mercury and DOC (3.4) 15%; Groundwater/surface water interactions (3.7) 5%.
Panel: N/A
Collaborators, Clients:
Primary clients for this project are the resource managers responsible for making restoration recommendations for Everglades (SFWMD, FDEP, USEPA, and USCOE), 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 additional ENR 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.

BACKGROUND NARRATIVES

Project Justification: The South Florida Water Management District (SFWMD) and U.S. Army Corps of Engineers (USACOE) have decided to move ahead with plans to construct man-made wetlands on reclaimed agricultural lands in the northern Everglades. Currently, the total project size is 3,975 acres, but when the project is fully implemented, it would encompass approximately 35,000 acres. The decision to move ahead for full implementation was impart based on our preliminary findings that methylmercury production and food-web accumulation rates are not exacerbated in the ENR compared to the more natural Everglades. However, two major questions remain unanswered: 1) will the ENR areas maintain as low methylmercury production sites on a long-term basis? and 2) what are the underlying fundamental reasons (processes) why methylmercury production is low. Answers to these questions are the focus of our ENR studies and will be provide fundamental information on how these areas are managed in the future.

Project Objectives: The overall objective of this project is to conduct intensive, process-oriented research that focuses on the primary mercury cycling pathways in the ENR, and to emphasize areas that may have management implications for restoration alternatives. The ENR is unlike any other area in the Everglades in terms of geochemistry, soils, and hydrology. As a result, our studies at the ENR are being conducted using a comparison/contrast approach with respect to results from the ACME project. Our operating hypothesis is that the ENR is an immature analog to the site in the eutrophied zone of Water Conservation Area 2A (WCA2A) (F1) the ACME project is investigating, and that with time mercury cycle in the ENR will mimic that site. To test this hypothesis, we have outlined three specific objectives: 1) determine what affect phosphorus, nitrogen, sulfur and DOC enriched waters draining, from the agricultural area into the ENR have on the major mercury cycling processes (methylation, demethylation, reduction/volatilization, sedimentation/resuspension, and bio-uptake/accumulation), 2) determine whether focused groundwater discharge and recharge areas within the ENR exacerbate or mitigate the mercury methylation process, and 3) assess whether decades of soil amendments to ENR soils served to promote or inhibit methylmercury production and release from porewaters.

Overall Strategy, Study Design, and Planned Major Products: This project is specifically designed to compliment mercury research efforts by other agencies and other USGS projects currently ongoing in the ENR. The SFWMD is conducting a mercury mass-balance study to account for inflows outflows and species shifts as water flows through the ENR; Oak Ridge National Lab is conductinc, mechanistic studies of mercury evasion from the ENR; Florida Game and Freshwater Fish Commission is conducting fish sampling surveys; Dr. Cindy Gilmour is conducting mercury methylation studies; and the USGS is conducting studies of nutrient cycling (Orem), mercury demethylation (Mark Marvin-Dipasquale), DOC characterization (Aiken), and quantifying groundwater/surface water exchange (Jud Harvey). This study will provide temporal and spatial information on mercury phase and species variability, with particular emphasis on trying to discern the dominant organic and inorganic ligands that complex methylmercury and control its transport and bioavailability. Repeated field trips to the same sites during the wet/dry and winter/summer periods and over a number of years will be necessary to ascertain if there are signs of "maturation" in this system, and if the major processes operating at site F1 are similar to those in the ENR. Major products produced by this effort include a Web accessible data base, yearly fact sheets summarizing progress to date, a Ph.D. thesis (Sue King, University of Wisconsin) and subsequent scientific journal manuscripts (about 3), and incorporation of these results into the overall ACME synthesis paper on mercury cycling in south Florida (likely a USGS professional paper).

WORK PLAN

The hydrology of the ENR is largely the result of the original design plan, so we are examining whether groundwater inflow versus outflow has an appreciable effect on the resultant geochemistry and mercury cycling. If it can be shown that certain hydrologic regimes are preferable in terms of low MeHg production, management can require these features into future design requirements for other ENR sites. In addition, we are evaluating the effect of vegetation heterogeneity on mercury levels and speciation and on general water chemistry. To date, we have collected surface water, porewater and sediments in an area containing emergent macrophytes (T. domingensis) and in an open water area where only floating vegetation (pistea and periphyton) were present. We are testing the hypothesis that oxygen diffusing from the roots of macrophytes may create microcosms effecting the cycling of mercury and sulfur species differently from areas without an oxygen source to the root zone. Dr. Stephen Lindberg has already shown that cattails are effect of removal "pumps" for gaseous mercury in sediments, and we suspect that vegetation also affects other parts of the mercury cycle. Dense cattail growth potentially would reduce light penetration to surface waters, potentially inhibiting photosynthesis (and, thus, oxygen production) in the surface waters, as well as photoreduction of mercury.

A primary goal of this research is to evaluate the partitioning behavior of mercury species in ENR sediments through calculation of Kd values, to evaluate the levels of sulfide and DOC in porewaters of differing groundwater- flow regimes and their potential influence on mercury levels in porewaters and sediments. Through evaluation of mercury (total and methyl) Kd values for these sediments, we should be able to answer questions about the transport of mercury species to/from the groundwater system. In addition, we will be focusing efforts on the use of ultrafiltration to determine the size ranges of DOC with which inorganic and methyl mercury are predominantly associated. Filtration separations will be done at < 10 K Dalton, 10 K Dalton < X <100 K Dalton, 100 K Dalton < X < .04 um, and < 0.04 um < 1.2 um. This work will be closely coordinated with Dr. George Aiken who will be using XAD resins to assess elemental and functional group characteristics of these DOC fractions.

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) Hg_total and methylmercury (MeHg) whole-water determinations of dissolved gaseous mercury (Hg⁰) and reactive mercury (Hg_R), 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. All mercury samples are transported via express mail to the Mercury Research Laboratory in Madison, Wisconsin.

A mercury cycling model that will incorporate ENR 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 various ENR management alternatives, and forecast the potential long-term effects of ENR-type systems on the mercury cycle for the Everglades.

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.

Timeline:

Project Timeline for Activities on the ACME Project

ACTIVITIES (person responsible)

FY1995 1995

FY1996 1996

FY1997 1997

FY1998 1998

FY1999 1999

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LAB/DATA ANALYSIS (Olson, Dewild, King)

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ANNUAL FACT SHEET (Krabbenhoft)

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Ph.D Dissertation (King)

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Manuscripts (Krabbenhoft, Olson, Hurley, Cleckner)

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MTG WITH CLIENTS (Krabbenhoft)

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ACME Project Deliverable Products Schedule

Product

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FY1996 1996

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Archival and Web Data Bases

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Synthesis Paper (review)

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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. Although one of the abstracts specifically addressed our results on ENR studies, most of the above mentioned products incorporate the ENR findings in their interpretations. In addition to Sue King's Ph.D dissertation, it is anticipated that 2-4 abstracts, and 3 manuscripts for scientific journal publication will be produced from our ENR studies along.

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. In addition, on about an annually basis formal meetings are held to discuss research findings and continually reformulate the research questions in an adaptive management framework. At these meetings a 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, and management plans to address nutrient removal and mercury toxicity concerns. The USEPA and USCOE are particularly interested in our findings since they are responsible for the permitting/EIS and design and operation of the ENR sites, respectively. Through these close and constant channels of communication, we anticipate being able to work together to meeting 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): During the past year, we have refocused our studies in the ENR to concentrate on the effects of site hydrology, water chemistry, and vegetation density. In addition, we are now operating under the hypothesis that the ENR is an immature analog to site F1, and we will be drawing upon close comparisons of these sites as a means of testing this hypothesis. Ultrafiltration separations of various size fractions of DOC and corresponding analytical determinations of the inorganic and MeHg concentrations of mercury in these size fractions is a new aspect to this program and will aid scientists and management in deciphering the effect vectors of mercury transport through the ENR.

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH

MAJOR FINDINGS:

• Aqueous Hg speciation in the ENR eveal spatial and seasonal patterns, although muted when compared to the more natural areas of the Everglades
• Reduced flows and stagnation of waters within the ENR lead to increases in both MeHg_U and particle-associated MeHg.
• Analyses of HgR and DGM suggests a reduced reactivity of aqueous Hg species in the ENR compared to southern sites.
• Aqueous samples from the ENR present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg). This problem was first revealed on samples taken from the ENR, we speculated due to abnormally high sulfide levels.
• 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:

PRODUCTS PRODUCED:

• 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.
• 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.

• 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.
• 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.
• 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.
• 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

NEEDS

Required Expertise

Needs/Personnel

FY1995 1995

FY1996 1996

FY1997 1997

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FY1999 1999

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Project Coordinator (Krabbenhoft)

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Lead Lab Analyst, Lab Assist. (King, Olson, Dewild)

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50% reduced

Ph. D. Candidate (Sue King)

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Mercury Research Lab. Madison, Wisconsin

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Web Data base assistant (Harry House)

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Names of Key Project Staff:
Krabbenhoft
King,Olson, Dewild
Sue King
Harry House

Major Equipment/Facility Needs: N/A

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