Grantee Research Project Results
2000 Progress Report: Hg and Fe Biogeochemistry
EPA Grant Number: R825433C016Subproject: 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: UC Davis Center for Children's Environmental Health and Disease Prevention
Center Director: Van de Water, Judith
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
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text | Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research
Objective:
To explore the biogeochemical processes controlling mercury (Hg) methylation and internal loading by nutrients, especially iron (Fe) and now sulfur (S).
Progress Summary:
Mercury (Hg) Biogeochemistry
Project B.5 is closely tied to Projects B.1 (Fish as transporters/modifiers of Hg), Project B.3 (Wildlife Bioaccumulation & Effects), B.6 (Water Motions & Material Transport) and B.8 (History of Anthropogenic Effects), but especially B.4 (Microbiology of Hg Methylation in Sediments). Our ongoing studies on Hg cycling and bioaccumulation in Clear Lake are also closely coordinated with our EPA Superfund project (associated with Hg contamination from the Sulphur Bank Mercury Mine), which is nearing completion and moving toward a stage where remediation options for the mercury mine site will be identified, probably within the next year.
All of the projects identified above deal with various aspects of the transport, fate and impacts of methyl Hg on the aquatic ecosystem of Clear Lake. Our previous studies had 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 eroded or 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 the 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 erosional source of Hg to Clear Lake. However, because of significant changes in precipitation and associated weather patterns in recent years, we have observed another alternative source (acid mine drainage discharging from the mine) which we believe represents the predominant source of Hg to Clear Lake since the closure of mining activities.
Our 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. Long-term projects like the Center program have enabled us to collect data over much longer periods of time, allowing us to observe the effects of natural inter-annual variability on the dynamics of various system components, such as methylation. During several recent winters we observed processes that have altered our 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 (see Project B.6) 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.
We 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 (see Project B.8). This past year we 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 (Upper Arm, Lower Arm and Oaks Arm - near the mine) are tested for methylation potential. We exposed these sediments to several treatments over 5 day periods, including sparging with oxygen (to produce oxygenated conditions) and nitrogen (to produce anoxic conditions). We 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, which is due to the USEPA by the Central Valley Regional Water Quality Control Board by June of 2001.
Our ongoing efforts at the Sulphur Bank Mercury Mine continue to emphasize analyses of Hg, other metals and various ions in water from the Herman Pit and within the ground water (as evidenced by on-site test well samples) and water flow from the Pit to the lake (involving dye and stable isotope tracer studies). Presently estimates derived from tracer studies indicate a flow rate of ca. 6,000-8,000 gpm out of the Herman Pit (presumably into Clear Lake), at least 1-2 orders of magnitude higher estimates than those recorded during the mining era (evidence from Project B.6 - Water motions & material transport). We are quantifying water movement in order to produce a water balance model that will enhance our understanding of the communication between the mine site and Clear Lake and thus improve our understanding of the mechanisms by which acid mine drainage is impacting the aquatic ecosystem of Clear Lake.
In addition to a water budget during the past year we have also begun developing a mercury budget for Clear Lake, including seasonal input sources such as streams from the watershed, lakebed springs, and of course the mine. Output components include transport out of Cache Creek (downstream to Yolo County and the San Francisco Bay-Delta) and some atmospheric efflux (although we are not measuring this ourselves, other researchers are addressing this component). Storage in Clear Lake sediments is a major component that must be accounted for in order to balance the source materials being derived from the mine's input annually. This portion of our program interfaces most closely with Project B.8 which is analyzing cores for deposition of mercury.
We are also now working closely with US Army Corps of Engineers to address the impacts of restoration of a wetland at the northwest region of Clear Lake through Rodman Slough and the former Robinson Lake (linked to Project B.2). This 1200 acre wetland area was diked to enhance agricultural production starting in the 1880s through a series of "Reclamation Projects". But, more recent recognition of the value of wetland rehabilitation projects has provided incentives to reverse this process and initiate "de-reclamation" by removing dikes/levees from this wetland. However, a process known as the "Newly Flooded Reservoir Syndrome" has shown that enhanced Hg methylation may persist in newly flooded soils for up to 10-20 yrs. The Army Corps of Engineers is presently considering a restoration/rehabilitation project for the entire 1200 acres. This could have added benefits for wetland restoration, yet cause indirect negative consequences in the form of elevated methyl Hg for biota in the wetland and/or Clear Lake. Identification of any additional sources of methyl mercury to Clear Lake is essential if we are to balance the mercury budget identified above. Preliminary estimates of water held and pumped from rice fields in this region indicate that these waters hold approximately 5X the methyl mercury concentration as normal input streams and Clear Lake water.
A new set of tracer studies (June and September 1998) in the mine's open Herman Pit, conducted by Schladow, Clark and Oton (see Project B.6 - Water motions & material transport) continue to suggest that the mine (via acid mine drainage) is a significant source of sulfate and lowered pH to Clear Lake. The use of SF6 and 22Ne tracers have confirmed earlier Rhodamine WT estimates of fluid flow rates from the Herman Pit, through waste rock piles and assumedly toward/into Clear Lake. Once this material reaches Clear Lake, we are addressing the fate of this acid mine drainage in the formation of floc and its interaction with the lake's biota. Sulfate loading and lowering of pH from acid mine drainage may be as important as Hg loading as an anthropogenic stress on Clear Lake increasing the bioaccumulation of Hg. Therefore, one of our new objectives has been to construct a sulfur budget for Clear Lake, including sources (such as streams, lakebed springs, atmospheric input and acid mine drainage) and sinks (such as stream outflow and sediment burial). During the past year we have developed a working mathematical model of sulfur flux within the sediments of Clear Lake which is based on known and estimated biogeochemical parameters of water and sediments within Clear Lake. Thus, eventually, we will have developed a mine water budget (to address acid mine drainage issues - see Project B.6), a sulfate budget (to address mercury methylation by microbes - see Project B.4) and a mercury budget (to address point source loading from the mine and storage in Clear Lake sediments, both historic and prehistoric).
We have begun a complete trophic analysis of mercury with the biotic compartments of Clear Lake. We 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 we are utilizing stable isotope analyses using 13C, 15N and 34S. In addition to data on mercury concentrations and stable isotopes, we 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 we should be able 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. Preliminary stable isotope analyses at Clear Lake have proven more complex than anticipated. As a result, we are now using another similar, but much more simple lake (Eagle Lake in the Sierra Nevada) as a companion system with which to compare the more productive and complex Clear Lake ecosystem. Initial samples have been collected and are being processed for all stable isotope and food web analyses.
Iron (Fe) Biogeochemistry
While this project has been closely tied to Project B.2 (Wetlands restoration) and our previously completed Clean Lakes Project, also funded by USEPA (which focused on nutrient loading, eutrophication and the production of noxious bluegreen algal blooms), most of our efforts during the past year have focused on the mercury and sulfur biogeochemistry rather than iron biogeochemistry. Previously one of the most interesting phenomena uncovered in our Clean Lakes investigation was an extraordinary increase in the mass of surplus phosphorus (P) 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. Since the P pool in the sediments that participates most strongly in the annual P cycle is the Fe-bound fraction, the inverse relationship between P and Fe in the water column is unexpected. The mass of surplus cycling P has declined since the return of years with heavier precipitation, but clear water conditions have persisted. Sulfate concentrations in lake water declined during the drought years, presumably due to lower loading both from Hg mining and from the rest of the watershed, implicating sulfate loading in nutrient recycling processes as well as Hg methylation.
Future Activities:
We will install passive flow meters in sediments in the immediate vicinity of the Sulphur Bank Mercury Mine in order to estimate flow rates of acid mine drainage from the site into Clear Lake. We already have isotopic data to indicate that the mine is producing and transporting sulfate and mercury laden fluids into Clear Lake and our next task is to quantify the actual flow rates that are reaching Clear Lake up through lakebed sediments. With these data we will better be able to constrain the upper and lower bounds of flow rate estimates into Clear Lake.
In the second phase of the Fe geochemistry project, we will concentrate on the problem of the Fe cycle in Clear Lake. Our previous work has demonstrated that Fe remains the limiting element for nitrogen (N) 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 become 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. In the future we plan to investigate the sediment and water column processes that currently drive Clear Lake into a Fe-limited state, and will apply these methods on a survey basis to several other lakes in California that are thought to be Fe limited.
Our new working hypothesis is that the interactions between the biogeochemical cycling of N and P, and especially of Fe and Hg are significantly driven by sulfate loading and local sediment acidification near the mine as well as direct loading by Hg, P, and especially Fe. Internal loading by Hg, Fe, and P in turn enter into multi-factorial and non-linear relationships that ultimately impact both the state of eutrophication of Clear Lake and the amounts 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 (socio-economic) 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. However, until we have a deeper understanding of the magnitude and annual variation in loading of sulfate and acidity to Clear Lake sediments, the framework for addressing iron cycling questions is not in place. Currently, this aspect of our program has been on temporary hold until we identify a new graduate student who is interested in working on this aspect of iron biogeochemistry in order to move further with testing our preliminary hypotheses regarding the influence of N, P and Fe in the production of cyanobacteria blooms, mercury methylation and the oxidation of organic sediments within Clear Lake.
Supplemental Keywords:
RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, ECOSYSTEMS, Waste, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Water & Watershed, Contaminated Sediments, mercury transport, Restoration, Aquatic Ecosystem, Environmental Microbiology, Terrestrial Ecosystems, Biochemistry, Environmental Monitoring, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Watersheds, Mercury, 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 runoffProgress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R825433 UC Davis Center for Children's Environmental Health and Disease Prevention 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
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.