Hg and Fe Biogeochemistry

EPA Grant Number: R825433C016
Subproject: this is subproject number 016 , established and managed by the Center Director under grant R825433
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
Title: Hg and Fe Biogeochemistry
Investigators: Suchanek, Thomas , Goldman, Charles R. , Richerson, Peter
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


This project seeks to explore the biogeochemical processes controlling mercury (Hg) methylation and internal loading by nutrients, especially iron (Fe) and now sulfur (S).


Investigators' recent studies on acid mine drainage indicate that substantial ongoing discharge from the mine produces a flocculent precipitate near the mine which, in turn, provides highly favorable conditions for mercury methylation. During several recent winters investigators observed processes that have altered their perception of how ongoing Hg contamination enters the Clear Lake ecosystem. Significant rainfall and associated flooding, run-off from the mine site and overflow of a pit lake (Herman Pit) has led to acid mine drainage from the waste rock piles and mine site in general. Water flowing over and through these waste rock piles is highly acidic (pH 2-3), strips Hg from the waste rock piles and when it enters the pH 8 waters of Clear Lake, produces a light, unconsolidated alumino-silicate precipitate (floc) that is high in Hg, high in sulfate and high in surface area. Cyanobacterial blooms during the summer can add a significant organic enrichment, producing the perfect conditions for Hg methylation by microflora. The resulting partially consolidated floc (high in methyl Hg) is then capable of being reintrained into the water column, transported by currents to distant parts of Clear Lake and taken up by plankton, benthic invertebrates and bioaccumulated in higher trophic levels, exactly the scenario we have observed in Clear Lake. These recent observations of floc may have derived from periods of exceptionally calm weather/water conditions at Clear Lake (which allowed the floc to accumulate in discrete clouds without being dispersed and transported to other regions of Clear Lake) or by generally increased flow of acid mine drainage from the mine site. More recent data suggests that the seepage of acid mine fluids is entering the waters of Clear Lake through sub-surface conduits, potentially seeping upward through the sediments. Our most recent data suggests that the flow of acid mine drainage is likely extending into Clear Lake at least 300 meters from the mine site.

Investigators are also continuing to investigate the historical record of Hg input to Clear Lake (both before and after mining) through a close coordination with the sediment coring project. This past year they have collected a new series of deeper cores (ca. 3 m in length), which are being analyzed for total mercury, methyl mercury, 210Pb (for dating) and a suite of other parameters (see B.8). Our most recent efforts to elucidate the biogeochemistry of mercury methylation involve an elaborate microcosm experiment in which short sediment cores from representative locations around Clear Lake are tested for methylation potential. They exposed these sediments to several treatments over 5 day periods, including sparging with oxygen (to produce oxygenated conditions) and nitrogen (to produce anoxic conditions). They also tested the strength of methyl mercury production from at least two different types of floc found very near the Sulphur Bank Mercury Mine. The difference in methyl mercury concentrations in overlying water in these cores from T0d to T5d provides an estimate of the production of methyl mercury from the range of conditions under which they were held. These results also will provide Hg loading data for developing a Total Maximum Daily Load (TMDL) criteria at Clear Lake.

Expected Results:

Investigators have begun a complete trophic analysis of mercury with the biotic compartments of Clear Lake. They are attempting to follow the flow of mercury from input stream terrestrial detritus, and autochthonous primary producers within Clear Lake to primary consumers and most major biomass producing species within this trophic system. To accomplish this they are utilizing stable isotope analyses using 13C, 15N and 34S. In addition to data on mercury concentrations and stable isotopes, they will also obtain data on gut content analyses for each major consumer within this system to help develop and verify a set of trophic web interactions for Clear Lake. By utilizing three stable isotopes and the diet data they hope to obtain a reasonably accurate tracing of whether mercury is being transported/bioaccumulated along the benthic pathway or the planktonic pathway within the Clear Lake aquatic ecosystem and describe more accurately trophic interactions. This will produce one of the first in depth studies of trophic transfer of mercury for any system studied to date.

Supplemental Keywords:

watershed, aquatic ecosystem restoration, Clear Lake, acid mine drainage, microbiology bioaccumulation, mercury methylation, biogeochemistry, nutrient loading, sulfur, iron., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Contaminated Sediments, mercury transport, Restoration, Aquatic Ecosystem, Environmental Microbiology, Biochemistry, Environmental Monitoring, Terrestrial Ecosystems, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Mercury, Watersheds, anthropogenic stress, contaminant exposure, mercury uptake, watershed management, biodiversity, Clear Lake watershed, contaminated marine sediment, microbial degradation, nutrient loading, aqueous mercury, acid mine drainage, agricultural watershed, contaminated sediment, marine biogeochemistry, restoration strategies, Clear Lake, integrated watershed model, bioremediation of soils, iron, methylmercury, aquatic ecosystems, environmental stress, contaminated groundwater, mercury methylation, ecosystem stress, ecological impact, mercury chemistry, ecological research, watershed restoration, acid mine runoff

Progress and Final Reports:

  • 1997
  • 1998
  • 1999
  • Final Report

  • Main Center Abstract and Reports:

    R825433    EERC - Center for Ecological Health Research (Cal Davis)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R825433C001 Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
    R825433C002 Sacramento River Watershed
    R825433C003 Endocrine Disruption in Fish and Birds
    R825433C004 Biomarkers of Exposure and Deleterious Effect: A Laboratory and Field Investigation
    R825433C005 Fish Developmental Toxicity/Recruitment
    R825433C006 Resolving Multiple Stressors by Biochemical Indicator Patterns and their Linkages to Adverse Effects on Benthic Invertebrate Patterns
    R825433C007 Environmental Chemistry of Bioavailability in Sediments and Water Column
    R825433C008 Reproduction of Birds and mammals in a terrestrial-aquatic interface
    R825433C009 Modeling Ecosystems Under Combined Stress
    R825433C010 Mercury Uptake by Fish
    R825433C011 Clear Lake Watershed
    R825433C012 The Role of Fishes as Transporters of Mercury
    R825433C013 Wetlands Restoration
    R825433C014 Wildlife Bioaccumulation and Effects
    R825433C015 Microbiology of Mercury Methylation in Sediments
    R825433C016 Hg and Fe Biogeochemistry
    R825433C017 Water Motions and Material Transport
    R825433C018 Economic Impacts of Multiple Stresses
    R825433C019 The History of Anthropogenic Effects
    R825433C020 Wetland Restoration
    R825433C021 Sierra Nevada Watershed Project
    R825433C022 Regional Transport of Air Pollutants and Exposure of Sierra Nevada Forests to Ozone
    R825433C023 Biomarkers of Ozone Damage to Sierra Nevada Vegetation
    R825433C024 Effects of Air Pollution on Water Quality: Emission of MTBE and Other Pollutants From Motorized Watercraft
    R825433C025 Regional Movement of Toxics
    R825433C026 Effect of Photochemical Reactions in Fog Drops and Aerosol Particles on the Fate of Atmospheric Chemicals in the Central Valley
    R825433C027 Source Load Modeling for Sediment in Mountainous Watersheds
    R825433C028 Stress of Increased Sediment Loading on Lake and Stream Function
    R825433C029 Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
    R825433C030 Mercury Distribution and Cycling in Sierra Nevada Waterbodies
    R825433C031 Pre-contact Forest Structure
    R825433C032 Identification and distribution of pest complexes in relation to late seral/old growth forest structure in the Lake Tahoe watershed
    R825433C033 Subalpine Marsh Plant Communities as Early Indicators of Ecosystem Stress
    R825433C034 Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
    R825433C035 Border Rivers Watershed
    R825433C036 Toxicity Studies
    R825433C037 Watershed Assessment
    R825433C038 Microbiological Processes in Sediments
    R825433C039 Analytical and Biomarkers Core
    R825433C040 Organic Analysis
    R825433C041 Inorganic Analysis
    R825433C042 Immunoassay and Serum Markers
    R825433C043 Sensitive Biomarkers to Detect Biochemical Changes Indicating Multiple Stresses Including Chemically Induced Stresses
    R825433C044 Molecular, Cellular and Animal Biomarkers of Exposure and Effect
    R825433C045 Microbial Community Assays
    R825433C046 Cumulative and Integrative Biochemical Indicators
    R825433C047 Mercury and Iron Biogeochemistry
    R825433C048 Transport and Fate Core
    R825433C049 Role of Hydrogeologic Processes in Alpine Ecosystem Health
    R825433C050 Regional Hydrologic Modeling With Emphasis on Watershed-Scale Environmental Stresses
    R825433C051 Development of Pollutant Fate and Transport Models for Use in Terrestrial Ecosystem Exposure Assessment
    R825433C052 Pesticide Transport in Subsurface and Surface Water Systems
    R825433C053 Currents in Clear Lake
    R825433C054 Data Integration and Decision Support Core
    R825433C055 Spatial Patterns and Biodiversity
    R825433C056 Modeling Transport in Aquatic Systems
    R825433C057 Spatial and Temporal Trends in Water Quality
    R825433C058 Time Series Analysis and Modeling Ecological Risk
    R825433C059 WWW/Outreach
    R825433C060 Economic Effects of Multiple Stresses
    R825433C061 Effects of Nutrients on Algal Growth
    R825433C062 Nutrient Loading
    R825433C063 Subalpine Wetlands as Early Indicators of Ecosystem Stress
    R825433C064 Chlorinated Hydrocarbons
    R825433C065 Sierra Ozone Studies
    R825433C066 Assessment of Multiple Stresses on Soil Microbial Communities
    R825433C067 Terrestrial - Agriculture
    R825433C069 Molecular Epidemiology Core
    R825433C070 Serum Markers of Environmental Stress
    R825433C071 Development of Sensitive Biomarkers Based on Chemically Induced Changes in Expressions of Oncogenes
    R825433C072 Molecular Monitoring of Microbial Populations
    R825433C073 Aquatic - Rivers and Estuaries
    R825433C074 Border Rivers - Toxicity Studies