aquatic cycling of mercury in the
Project Proposal for 1998
Program: FRAGILE ENVIRONMENTS
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.
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.
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.