Mercury and Iron Biogeochemistry

EPA Grant Number: R825433C047
Subproject: this is subproject number 047 , 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: Mercury and Iron Biogeochemistry
Investigators: Suchanek, Thomas , Richerson, Peter
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: June 30, 1992 through June 30, 1996
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research


The primary focus of this project is to better understand the biogeochemical processes controlling mercury (Hg) methylation and internal loading by nutrients, especially Iron (Fe).


Previous studies have focused most closely on lakebed sediments as the source of ongoing Hg input to Clear Lake. It was believed that this source originated from waste rock being bulldozed into Clear Lake during the mining years (ending about 1957), and subsequent erosion of waste rock piles along the shoreline of the lake during winter rains. This interpretation was based on several previous studies and our own data that were collected essentially during drought years in California, when no other source was known. In 1992 USEPA remediated a portion of the waste rock piles at the shoreline of the lake, reducing the angle of the slope, revegetating it and adding rip-rap to the base of the slope, essentially eliminating that major source of Hg to Clear Lake. However, because of significant changes in precipitation patterns in recent years, we have observed an alternative process which we believe represents the dominant source of Hg to Clear Lake since the closure of mining activities, acid mine drainage.

Investigators have been able to collect data over long periods of time, enabling them to observe the effects of natural inter-annual variability on the dynamics of various system components. The investigators have observed processes that alter 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. Water flowing over and through these waste rock piles becomes 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 aluminum silicate precipitate that is high in Hg, high in sulfate and high in surface area. Cyanobacterial blooms during the summer 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 into higher trophic levels, exactly the scenario we have observed in Clear Lake. They will also investigate the historical record of Hg input to Clear Lake (both before and after mining) through a close association with the sediment coring project. Their efforts on Hg methylation during this next phase of the Center program will be primarily to enhance our understanding of the interactions between the biogeochemistry of Hg and other metals at the mine site, their interaction with cyanobacterial blooms and the ultimate impact on Clear Lake's aquatic ecosystem, linking this closely with historical evidence derived from the coring project.

With respect to nutrient loading one of the most interesting phenomena uncovered in that investigation was an extraordinary increase in the mass of surplus phosphorus cycling in Clear Lake during the drought years of the late 1980s and early 1990s. This increase was apparently associated with a substantial reduction in available Fe, and a considerable reduction in algal biomass. This mass of surplus P and clear water conditions have persisted through the two wetter years that have occurred in the mid 1990s.

Expected Results:

Investigators work has demonstrated that Fe remains the limiting element for nitrogen fixation in Clear Lake. Fe and N co-limit algal growth. Some evidence suggests that Fe is the geochemically limiting element in a number of alkaline western lakes. Anthropogenic effects can thus cause eutrophication by directly increasing the N load of a lake (as occurs in Lake Tahoe), or indirectly by increasing Fe loading or recycling (as apparently happens at Clear Lake). Ultimately, most Fe/N limited lakes are liable to became P limited as anthropogenic N loads continue (as at Lake Tahoe, and perhaps marginally in past years at Clear Lake), with attendant changes in the productivity and species composition of the plankton. Relieving Fe limitation before P becomes limiting encourage cyanobacterial blooms, as observed at Clear Lake.

Investigators expect to prove their hypothesis that the interactions between the biogeochemical cycling of N and P, and especially of Fe and Hg, yield multi-factorial and non-linear relationships that ultimately impact both the state of eutrophication of Clear Lake and the levels of methylmercury that are transferred from lower trophic levels to bioaccumulate in top predators such as the osprey and edible largemouth bass and catfish. These endpoints have significant implications for the human dimensions (socioeconomic) component of Clear Lake's resources, and our efforts will ultimately produce policy-relevant decision points which will improve both ecosystem health and societal appreciation and utilization of these natural resources.

Supplemental Keywords:

Watershed, bioavailability, ecosystem stress, Clear Lake, biogeochemistry, mercury methylation, iron, eutrophication., RFA, Scientific Discipline, Toxics, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, mercury transport, Environmental Chemistry, Geochemistry, HAPS, Restoration, Fate & Transport, Microbiology, Environmental Microbiology, Biochemistry, Aquatic Ecosystem Restoration, Engineering, Geology, West Coast, 33/50, Environmental Engineering, contaminated sediments, mercury loading, Clear Lake, Sulphur Bank Mercury Mine, mining, biogeochemical cycling, methylation, methylmercury, iron, mercury methylation, mercury & mercury compounds, Mercury Compounds

Progress and Final Reports:

  • 1992
  • 1993
  • 1994
  • Final

  • 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