Microbiology of Mercury Methylation in Sediments

EPA Grant Number: R825433C015
Subproject: this is subproject number 015 , 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: Microbiology of Mercury Methylation in Sediments
Investigators: Nelson, Douglas
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 relationships between microbial methylation of mercury and reduction of sulfate and other microbial activities in Clear Lake sediments and to establish linkages between acid mine drainage, fluxes of inorganic mercury and production of methyl mercury in lake sediments near the mine.


In previous years, studies with structured sediment microcosms (core tubes) revealed that sediment from the Oaks Arm "floc" (OA-F) site emitted methyl mercury to the overlying water at rates roughly 20-fold higher than sediments from the other test sites in Clear Lake. Furthermore it was determined that for this sediment site (roughly 30 m off shore from a portion of the waste-rock pile of the Sulphur Bank Mine) that the characteristic porewaters are acidic (pH < 4.0) and very high in soluble sulfate (20 - 80 mM). This is by contrast to the bulk of Clear Lake sediments, which are characterized by porewaters of slightly alkaline pH and sulfate concentrations of approximately 0.1mM or less.

During the last year detailed surveys showed that the sediment area impacted by acid mine drainage runs for several hundred meters along the rip-rap and can extend up to 100 m off shore. Sulfate concentrations at the OA-F site were seasonally variable with maxima of 200 to 300 mM. At various standard sampling sites in Clear Lake it was previously established through the use of molybdate (a specific inhibitor of sulfate-reducing bacteria) that only about one-third of methylation potential is attributable to sulfate-reducing bacteria. However, this has not been tested specifically at the OA-F site. Because of the high concentrations of organic matter, sulfate and dissolved mercury at this site, sulfate-reducing bacteria may play a special role in the very high rates of methylation observed there. During the current period, sulfate- and iron reducing bacteria have been isolated from the OA-F and another "hotspot" site (Site 15), and these are in the process of being tested for mercury methylation potential and acid tolerance.

Expected Results:

The investigators hope to determine the upward flux of soluble inorganic mercury from sediments to overlying water at hotspot sites is our highest priority and pertains to the EPA plans to remediate this site. Establishing the full lateral extend of the impact of acid mine drainage on Clear Lake sediments coupled with representative mercury flux data will be extremely useful in estimating the flows of sulfate and mercury from the Sulphur Bank Mine into Clear Lake. Future studies of methyl mercury evolution from core tube microcosms will be used to map the complete area of high efflux. Molybdate inhibitor studies will be used to assess the importance of sulfate-reducing bacteria in the production of methyl mercury at the hotspots. They also expect to use artificial floc, treated in various ways, to determine which component (acidity, soluble mercury, elevated sulfate) is responsible for elevated methyl mercury production at the floc sites.

Supplemental Keywords:

watershed, aquatic ecosystem restoration, Clear Lake, acid mine drainage, microbiology bioaccumulation, mercury methylation., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Water, TREATMENT/CONTROL, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Contaminated Sediments, mercury transport, Treatment Technologies, Restoration, Aquatic Ecosystem, Environmental Microbiology, Biochemistry, Terrestrial Ecosystems, Bioremediation, Ecology and Ecosystems, Soil Contaminants, Aquatic Ecosystem Restoration, Mercury, Watersheds, anthropogenic stress, contaminant exposure, mercury uptake, watershed management, biodiversity, Clear Lake watershed, contaminated marine sediment, microbial degradation, aqueous mercury, acid mine drainage, agricultural watershed, contaminated sediment, fish-eating birds, marine biogeochemistry, restoration strategies, Clear Lake, integrated watershed model, bioremediation of soils, contaminants in soil, 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