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projects > geochemistry of wetland sediments > 1998 proposal

Geochemistry of Wetland Sediments from South Florida

Project Proposal for 1998

Program: FRAGILE ENVIRONMENTS (Formerly Ecosystems Program)
Project Title: Geochemistry of Wetland Sediments from South Florida: Biogeochemistry of C,N,P, and S, Relation of S to Methylation of Mercury, and Geochemical History
Location of Study Area: South Florida
Project Start Date: 10/1/95
Project End Date: 9/30/99
Project Number: 7230-37222
Project Chief: William H. Orem
Region/Division/Team/Section: Eastern/Geologic/ Eastern Energy Resource Surveys/NA
Phone: 703-648-6273
Fax: 703-648-6419
Mailing Address:
U.S. Geological Survey, National Center, ms 956, Reston, VA 20192
Program Element(s)/Task(s)
3.1(40%), 3.2 (35%), 6.8 (25%)
Collaborators, Clients:
USGS Collaborators - (1) USGS ACME group (D. Krabbenhoft, J. Hurley, C. Gilmour, G. Aiken, M. Reddy, and others) for studies on the relation of sulfur to mercury methylation in wetlands of south Florida. We co-sample and exchange information with this group on a regular basis. (2) J. Harvey for studies of hydrologic flux and nutrient gradients in the Everglades and the ENR. We have co-sampled with Judd and exchange information. We are also exploring the possible use of uranium and uranium isotopes as a groundwater tracer in south Florida wetlands. (3) USGS paleoecology group (Brewster-Wingard, Willard, and Ishman) for ecosystem history studies. We are attempting to tie changes in downcore sediment geochemistry to historical changes in the biota. We co-sample and exchange information regularly with this team. (4) Chuck Holmes and USGS sediment dating team. We co-sample with this group and regularly exchange information. The sedimentation rates provided by Chuck are key elements of our geochemical modeling efforts. (5) USGS Florida Bay group (B. Halley and others). We have interacted with this group on our Florida Bay studies to some degree, and hope to have more interaction as we acquire more data. (6) J.K. Bohlke on nutrients in ground water. We have just started some interaction with J.K. Bohlke on nutrients and organic carbon in Florida Bay sediments. This interaction should increase during the coming year.
Outside Collaborators- (1) D. Rudnick, F. Sklar and others (SFWMD) for our work on nutrient cycling and biogeochemical processes in Florida Bay sediments and the mangrove areas, and on the seagrass history study in Florida Bay. (2) L. Fink , P. Rawlick and others (SFWMD) for our studies on the relation of sulfur to mercury methylation, and organic diagenesis studies in the Everglades. (3) T. Atkinson and others (FDEP) for sulfur/methyl mercury studies. (4) T. Armantano and others (NPS/Everglades National Park) for our nutrient and sulfur studies in Taylor Slough and Florida Bay. (5) T. Fontaine and others (SFWMD) for our nutrient studies in the Water Conservation areas. (6) S. Newman (SFWMD) for our studies in the ENR study site. (7) Bill Louda (FAU) for studies of organic diagenesis and depositional history of Florida Bay.


Project Summary: This project is examining (1) sources of nutrients, sulfur, and carbon to wetlands of south Florida, (2) the important role of chemical and biological processes to the wetland sediments (biogeochemical processes) in the cycling of these elements, and (3) the ultimate fate (i.e. sinks) of these elements in the ecosystem. The focus on nutrients and carbon reflects the problem of eutrophication in the northern Everglades, where excess phosphorus from agricultural runoff has dramatically altered the biology of the ecosystem. Results will be used by land and water managers to predict the fate of nutrients (especially phosphorus) in contaminated areas of the Everglades, and to evaluate the long-term effectiveness of buffer wetlands being constructed as nutrient removal areas. Studies of sulfur in the ecosystem are important for understanding the processes involved in mercury methylation in the Everglades. Methyl mercury (a potent neurotoxin) poses a severe health risk to organisms in the south Florida ecosystem and to humans. Sediment studies being conducted by this project will also be used to construct a geochemical history of the ecosystem. An understanding of past changes in the geochemical environment of south Florida will provide land and water managers with baseline information on what water quality goals for the ecosystem should be, and on how the ecosystem has responded to past environmental change and will likely respond to the changes that will accompany restoration.

Project Justification: This project addresses three major areas of interest to land and water managers in south Florida: (1) nutrients and eutrophication of the Everglades, (2) the role of sulfur in the methylation of mercury and its bioaccumulation, and (3) the geochemical history of the south Florida ecosystem. Our nutrient studies are focused on using isotope methods (uranium/uranium isotopes, 18O of phosphate, 15 N, 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 the nutrient model for 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 artificial buffer wetlands or Stormwater Removal Areas (e.g. mostly cattail peat) be effective for the 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 sulfur within the ecosystem relate directly to the issue of methyl mercury production and bioaccumulation within the ecosystem, a serious threat to both wildlife and to the human population. Microbial sulfate reduction in wetlands (an anaerobic process) is the principal process for the methylation of mercury. Recent findings show that for south Florida wetlands methyl mercury 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, 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". We are emphasizing co-sampling with USGS mercury researchers (ACME team).

The geochemical history component of this project 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 quality goals needed to achieve "restoration" of the ecosystem. It will also provide land managers with an estimate of the range of water quality 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. Geochemical history studies in the southern part of the south Florida ecosystem are focused on (1) historical salinity change in the Taylor Slough area, and (2) the use of organic markers and stable isotopes to examine seagrass history in eastern Florida Bay. Both of these topics are of interest to land and water managers in south Florida.

From the beginning, one goal of this project has been to remain flexible and responsive to the needs of land and water managers in south Florida. As a result, project goals, while remaining largely intact, have been altered to reflect management and regulatory needs. This will continue to be a priority through the anticipated end date of this project.

Project Objectives: Major project objectives are as follows - (1) use isotope and other tracer methods to examine the major sources of nutrients, carbon, and sulfur to the south Florida ecosystem, (2) use geochemical methods to examine the major forms of nutrients, carbon, and sulfur in the sediments, the stabilities of the observed chemical species, and sinks of these elements in the sediments, (3) examine the biogeochemical processes controlling the cycling of nutrients, carbon, and sulfur in the ecosystem, and use geochemical modeling of porewater and sediment chemical data to determine the rates of these recycling processes, (4) develop geochemical sediment budgets for nutrients, carbon, and sulfur on a regional scale, including accumulation rates of these elements in the sediments, fluxes out of the sediments, and sequestration rates, (5) collaborate with mercury projects (USGS ACME team and others) to examine the role of sulfur and sulfate reduction in the production of methyl mercury in wetlands of south Florida, and the bioaccumulation of mercury in fish and other wildlife, (6) develop a geochemical history of the south Florida ecosystem from an examination of changes downcore in the concentration, speciation, and isotopic composition of nutrients, carbon and sulfur; use organic marker compounds and stable isotopes to develop a model of seagrass history in Florida Bay, (7) incorporate information from nutrient studies in overall ecosystem nutrient model, and results from sulfur studies in ecosystem mercury model.

Overall Strategy, Study Design, and Planned Major Products: This project uses both field studies and laboratory experiments to examine the biogeochemical cycling of nutrients, carbon, and sulfur in sediments. Field studies involve the collection of surface water, vegetation, sediment cores, and sediment porewater for chemical analysis. Appropriate protocols are used for the collection of samples and for chemical analysis. Sampling areas were selected to cover as wide an area as possible in the initial reconnaissance stages of the project. More recently, sampling areas were selected to reflect specific processes to be studied. Thus samples for examining sources of nutrients and sulfur to the Everglades have focused on canals draining the EAA. Biogeochemical cycling studies have focused on eutrophied and pristine sites for nutrients, and on areas of high and low methyl mercury production for the sulfur studies. Sampling sites were also chosen based on recommendations and requests from land and water management agencies. Emphasis on Taylor Slough and ENR reflects the needs of managers to understand the effects of proposed remediation efforts on the ecosystem. Isotope studies provide information on the sources of nutrients, carbon, and sulfur to the ecosystem, and information on biogeochemical cycling. Studies of nutrient, carbon, and sulfur speciation in sediments provides information on the processes occurring in sediments and on the major sinks for these elements in the sediments. Porewater studies are particularly useful for determining the major biogeochemical processes in sediments and for geochemical modeling aimed at quantitative estimates of reaction and recycling rates, and fluxes of chemical species between sediments and surface waters. Organic geochemical studies of sediments are useful for examine differences in chemical reactions among various sediments types (e.g. cattail peat and sawgrass peat), and how this may affect the ecosystem. Laboratory studies are primarily aimed at validating and extending observations from field studies. Laboratory studies will be emphasized more in FY 1998 and 1999. Experiments to be conducted will include: (1) laboratory decomposition of cattail and sawgrass under different simulated environmental conditions, (2) estimation of diffusion coefficients for nutrients and sulfate using a diffusion cell approach, and (3) adsorption studies of nutrients on various organic substrates (i.e. cattail peat, sawgrass peat, marl peat). Geochemical history studies emphasize analysis of dated cores, thus co-sampling with the USGS dating team is essential. Core samples are typical shared with the USGS paleontology group. Sampling sites are chosen in areas of suspected recent environmental change (e.g. lower Taylor Slough saltwater intrusion), areas of continuous sediment accumulation (Florida Bay sites), and to reflect different regions of the ecosystem. Planned major products include: (1) a series of presentations at local and national meetings (both scientific and managers meetings), (2) a series of USGS Open-File reports which will contain all data generated from the project, (3) a series of papers in scientific journals incorporating key pieces of-the data sets and focusing on specific aspects of the overall study, (4) a number of Fact Sheets designed for public information, (5) a chapter in a USGS book on south Florida describing the overall project, and containing key data, and references to all published reports, (6) CD-ROMS containing data from the project in GIS format, (7) a WEB site for public access to reports and data from this project.


Overall: This project originated as three separate projects and still retains three principal objectives: (1) examine the sources, sinks, and biogeochemical cycling of nutrients, carbon, and sulfur in wetland sediments of south Florida, (2) examine the relation between sulfur geochemistry in the Everglades and mercury methylation, and (3) develop a geochemical history of the ecosystem from a study of sediment cores. The project area and sampling sites are shown in the two attached maps. Areas sampled include most types of environments in south Florida, including the EAA, ENR, Water Conservation Areas, Big Cypress National Preserve, Everglades National Park (Shark Slough, Taylor Slough, mangrove fringe zone, and Florida Bay). Major sampling emphasis has been placed on EAA canals, marshes in the Water Conservation Areas, Taylor Slough and its mangrove fringe, and northeastern Florida Bay. Sampling methods employed include piston coring, pore water extraction by mechanical squeezing of cores, and grab sampling of surface waters. Clean techniques are utilized at all times. Chemical analysis of sensitive chemical species (sulfide, nutrients, etc.) are carried out in the field. Other samples for chemical analysis are appropriately preserved and returned to the laboratory for analysis. Samples are routinely provided to the USGS paleontology group, the metals in sediments group (Kotra/Gough), the ACME group (Krabbenhoft et al.), and others as requested. Chemical data is initially recorded in laboratory notebooks, then transferred to spreadsheets (MS Excel), and finally transferred to GIS databases (Arcview) for storage and transfer. Data will also be available in a series of published reports, and on a WEB site we plan to establish in FY 1998.

FY 1998 - (1) Continue temporal variability studies of nutrients, carbon, and sulfur in the northern Everglades. Study completed by 4/98. Open-File report completed by 9/98. Scientific paper completed in FY 1999 (Orem/Lerch). (2) Two Open-File reports on Taylor Slough work, one on porewater studies completed by 6/98, and one on sediment geochemistry completed by 9/98. Completion of Taylor Slough sampling will be accomplished by 6/98 (Orem/Lerch). (3) Laboratory decomposition studies begun by 12/97, scheduled to run 1 year (Orem/Lerch). (4) Complete study of sources of phosphorus to the Everglades using uranium isotopes by 12/97 (Zielinski) and 18O of phosphate by 6/98 (Kendall et al.). Report on uranium work by 6/98 and on 18O of phosphate work in FY 1999. (5) Complete work on sources of sulfur to the Everglades by 9/98 (Bates/Orem). Report out in FY1999. (6) Continue Florida Bay work; sampling in 10/97 and analytical work throughout FY 1998. Report out in FY 1999.
FY1999 - (t) Complete all analytical work on field samples by 12/98. (2) Complete all laboratory simulation studies by 6/99. (3) Complete report on seagrass history study by 6/99. (4) Complete paper on nutrient cycling in the Everglades by 12/98. (5) Complete Open-File report on Florida Bay sediment studies by 2/99. (6) Complete Open-File report on laboratory decomposition studies by 9/99. (7) Complete synoptic paper on project by 10/99.

Planned Deliverables/Products:
FY1997 - (1) Taylor Slough Fact Sheet, (2) Open-File Report on sediment geochemistry (C, H,N, S,Ash, Carbonate) from Water Conservation Areas and Everglades National Park, (3) Open-File Report on porewater geochemistry from Water Conservation Areas and Everglades National Park, (4) Paper on sulfur geochemistry in the northern Everglades (5) Paper on sulfur isotope and speciation in peat of the northern Everglades.
FY1998 - (1) Open-File report on the seasonal variability in porewater chemistry in the northern Everglades, (2) scientific paper on the use of uranium concentrations and uranium isotopes as a proxy for sources of phosphate to the Everglades, (3) Open-File report on porewater geochemistry of Taylor Slough, (4) Open-File report on sediment geochemistry (C, H,N,S,P,Ash. Carbonate) in Taylor Slough, (5) Paper on phosphorus geochemistry of the Everglades.
FY1999 - (1) Paper on seagrass history in Florida Bay from geochemical study of sediment cores, (2) Paper on nutrient cycling in the Everglades, (3) Open-File report on laboratory decomposition experiment, (4) Open-File report on geochemistry of Florida Bay sediments, (5) Synoptic paper on project for USGS publication.

Planned Outreach Activities: A Fact Sheet and the establishment of a WEB site are planned for FY 1998 to address public outreach needs. Client needs are being addressed in a number of different ways: (1) frequent calls and visits to collaborators (D. Rudnick, F. Sklar, L. Fink, P. Rawlick, T. Fontaine, S. Newman, all at SFWMD, and T. Armantano at NPS-ENP), (2) presentations at science conferences and program reviews in south Florida, (3) presentations at USGS meetings in south Florida, and (4) distribution of reports to interested clients. We are currently working closely with D. Rudnick and F. Sklar (SFWMD) on a comparison of porewater versus benthic chamber methods for determining nutrient fluxes from Florida Bay sediments. Also, we plan on participating in a study with L. Fink and others (SFWMD) to examine the effectiveness of cattail peat as a phosphorus trap.

Prior Accomplishments in Proposed Area of Work:

New Directions, Expansion of Continuing Project (if applicable): No new directions.


Accomplishments and Outcomes, Including Outreach: (1) Continued study of temporal variability in nutrient and sulfur biogeochemical processes in the northern Everglades sampling was conducted in December 1996, April 1997, and July 1997 at four sites in the northern Everglades. Results show that large variability in sulfide concentrations occurs at all sites indicating large variations in the rates of sulfate reduction. This suggests large temporal variability in mercury methylation rates. Results presented at Mercury Science meeting in May 1997. (2) Continued study of geochemistry of Taylor Slough. A second sampling expedition to Taylor Slough involving 10 USGS personnel was undertaken in May 1997. Fifty cores were obtained from 17 different sites for geochemistry and dating. Over 60 cores from 14 different sites were collected from Taylor Slough in May/June 1996. Preliminary results show that the mangrove fringe area bordering Florida Bay is an important zone for phosphorus sequestration in south Florida. Sample analysis is still underway. Results were presented at the Florida Bay Science Conference in December 1996. (3) Cores from Florida Bay obtained in June 1996 are being analyzed. Some preliminary results suggest that both lignin analysis and stable carbon isotope analysis are fruitful proxies for examining seagrass history. Phosphorus concentrations were observed to be very low in both porewater and sediments of Florida Bay. Concentrations of sulfide in Florida Bay porewater were observed to be extremely high, but sedimentary concentrations of sulfur were very low. The high porewater sulfides likely preclude significant methyl mercury production in Florida Bay sediments. Thus, methyl mercury observed in Florida Bay fish may be derived from freshwater fish from the Everglades consumed by saltwater species in estuarine or brackish water areas of the mangrove zone.

Deliverables, Products Completed:
Presentations and abstracts - (1) Florida Bay Science Conference, Key Largo, FL, Dec. 1996 (2 abstracts), (2) USGS Mercury Meeting, Madison, Wl, Nov. 1996 (no abstract), (3) South Florida Mercury Science Program Annual Workshop, Madison, WI, May 1997 (abstract - invited), (4) Annual USGS South Florida Program Meeting, Ft. Lauderdale, FL, August 1997 (3 abstracts), (5) South Florida Ecosystem History Program Annual Workshop, Key Largo, FL, October 1997 (abstract).
Publications - (1) Orem, W.H., Lerch, H.E., and P. Rawlick (1997) Descriptive geochemistry of surface and pore water from USGS 1994 and 1995 coring sites in south Florida wetlands. USGS Open-File Report, 70 pp. (in press).
Orem, W.H., Bates, A.L., Lerch, H.E., and P. Rawlick (1997) The geochemistry of sulfur in the northern Everglades. Limnol. Oceanogr. (in review).
Bates, A.L., Spiker, E.C., and CW. Holmes (1997) Speciation and isotopic composition of sedimentary sulfur in the Everglades Water Conservation Area 2A, Florida, USA. Chemical Geology (in review).
Orem, W.H., Lerch, H.E., and Bates, A.L. (1997) General geochemistry of sediments from wetland areas of south Florida. USGS Open-File Report (in preparation).
Fact Sheet-(1) Geochemical Studies in Taylor Slough and Northeastern Florida Bay (in preparation).


Required Expertise:
FY1998 - All expertise needs are staffed in project or are acquired by collaboration with other USGS projects, or collaboration with researchers in outside agencies (e.g. SFWMD, FDEP, FGS, USEPA, NPS, USFWS, USDA). Principal expertise needs include: organic geochemistry, porewater geochemistry, sulfur geochemistry, isotope geochemistry, uranium geochemistry, geochemical modeling, GIS and computer data handling, trace metal geochemistry, mercury geochemistry and microbiology (collaboration with USGS ACME team), paleoecology (collaboration with USGS paleoecology group), hydrology (collaboration with Judd Harvey- USGS, and SFWMD), agricultural fertilizer usage (collaboration with B. Glasz, USDA).
FY1999 - Same as FY1998.

Names of Key Project Staff:
FY 1998 - Reston, VA: William H. Orem (project chief/geochemist), Harry E. Lerch (laboratory chemist, field assistant), Anne L. Bates (sulfur chemist/isotope chemist), Cheryl Hedgman (GIS and data specialist, laboratory assistant), Margo Corum (student aid-laboratory and field assistant), Ann Boylan (student aid-laboratory and field assistant). Denver, CO: Robert Zielinski (geochemist-uranium and uranium isotope geochemistry). Menlo Park, CA: Carol Kendall (res. hydrologist-stable isotope geochemistry), Cecily Chang (res. hydrologist-stable isotope geochemistry), J. Langston (hydrologic tech-stable isotope geochemistry). St. Petersburg, FL: Sharon Fitzgerald (geochemist-organic diagenesis and seagrass history, Florida Bay).
FY 1999 - Reston, VA: William H. Orem (project chief/geochemist), Harry E. Lerch (laboratory chemist, field assistant), Anne L. Bates (sulfur chemist/isotope chemist), Cheryl Hedgman (GIS and data specialist, laboratory assistant), Margo Corum (student aid-laboratory and field assistant), Ann Boylan (student aid-laboratory and field assistant). Denver, CO: Robert Zielinski (geochemist-uranium and uranium isotope geochemistry). Menlo Park, CA: Carol Kendall (res. Hydrologist-stable isotope geochemistry), Cecily Chang (res. Hydrologist-stable isotope geochemistry), J. Langston (hydrologic tech.-stable isotope geochemistry). St. Petersburg, FL: Sharon Fitzgerald (geochemist-organic diagenesis and seagrass history, Florida Bay).

Major Equipment/Facility Needs: Geochemical laboratories are located in Reston, VA. Stable Isotope laboratories are located in Reston, VA and in Menlo Park, CA. Uranium laboratory is located in Denver. CO. No new major equipment needs anticipated for FY 1998.

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