Grantee Research Project Results

Final Report: The History of Anthropogenic Effects

EPA Grant Number: R825433C019
Subproject: this is subproject number 019 , 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: The History of Anthropogenic Effects
Investigators: Richerson, Peter , Nelson, Douglas , Anderson, Daniel , Suchanek, Thomas
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

Objective:

The overall objective of this research project was to raise sediment cores from Clear Lake, California to investigate multiple stresses on the lake since European settlement in the 1800s. The two most important questions we hoped to answer were the timing of the mercury contamination of the lake and the timing of the advent of cyanobacterial blooms. Both have been hypothesized to be recent effects of human disturbance—mining in the case of mercury and increased sediment loading in the case of eutrophication and cyanobacterial blooms. Also, earlier investigators suggested the hypothesis that the use of heavy earthmoving equipment, which began in the late 1920s, was responsible for erosion, mercury, and habitat loss stresses, and we considered our findings in terms of this hypothesis.

Summary/Accomplishments (Outputs/Outcomes):

We obtained multiple cores from all three subbasins of the lake. The cores are approximately 2.5 m long and span as much as 3,000 years of the lake's history, according to ¹⁴C dates from the bottoms of the cores. Total (primarily inorganic) mercury, methylmercury, and several other parameters were measured at 5-cm intervals down the core. Nearly all of the parameters show major changes at depths of 57.5-135 cm, corresponding to an estimated date of 1927 (²¹⁰Pb). Accepting this date for the similar major changes in all four cores yields an estimated 1.23 cm year^-1 average post-1927 sedimentation rate. Organic matter, total carbon, water content, and total nitrogen all show significant decreases above this depth. A peak in inorganic deposition rate and minimum values for percent water is present at a depth corresponding approximately to the year 1970. Both total and methylmercury concentrations show major increases in concentration (roughly tenfold) above the 1927 horizon. There also is a smaller uptick in total and methylmercury 60-65 cm below the 1927 horizon in Upper Arm cores that could represent the beginning of mercury production at the Sulphur Bank Mercury Mine (SBMM) in 1873. If so, sedimentation rates from 1873-1927 were 1.17 cm/year. ¹⁴C dates are not entirely trustworthy in Clear Lake because of contamination with depleted ¹⁴C from numerous geothermal gas wells that vent into the bottom of the lake. Estimates based on these dates yield a pre-European sedimentation rate of about 1 mm/year. Total mercury levels peaked in the 1960s (last mining was in 1957), and a modest decline has occurred since that time. Methylmercury profiles are more complex.

Interestingly, the first 75 years of European settlement in the Clear Lake Basin (including the most productive years of the SBMM) appeared to have barely detectable effects on mercury deposition. Changes since 1925 are much more dramatic. The large increase in mercury levels beginning in approximately 1927 corresponds to the use of heavy equipment to exploit the ore deposit at the SBMM with open pit methods.

The following activities were accomplished:

• We confirmed that sediment inflow into Clear Lake became a major stressor after European settlement. This finding has contributed to efforts to improve water quality at Clear Lake. As long as it was possible to characterize the lake's water quality problems as natural, many citizens and regulators did not deem remediation efforts necessary or appropriate. Now Clear Lake managers are planning a project to restore a major wetland on the lake’s most important tributary.

• We confirmed that mercury and acidity from the SBMM became major stressors when the mine was operated with open pit methods, and that this stress continues. This finding continues to drive efforts to remediate the mine. It formed a significant part of our recommendations to the U.S. Environmental Protection Agency Superfund regarding the role of the SBMM in discharging mercury into the lake.

• We suggest that sedimentation rates may reflect the detrimental impacts of overgrazing near the lake in the late 19th century. This information provides Clear Lake-area farmers with a reminder of the environmental consequences of overly intensive agricultural practices.

• Our sediment samples reveal no signs of declining inorganic mercury concentration resulting from remediation work conducted at the mine in the early 1990s. This information may compel environmental restoration planners to refine their approaches to remediation projects at Clear Lake.

• Our findings are consistent with a long-standing hypothesis that accelerated disturbance by heavy machinery beginning in the 1920s was an important 20th century stress on the Clear Lake ecosystem. Drier sediments with less organic matter and nitrogen are consistent with a greater ratio of inorganic to organic deposition. In addition to the internal data from the cores, the historical evidence suggests a significant increase in watershed disturbance around 1927. At that time, people began applying powered earthmoving technology to streambed gravel mining, road construction, wetland reclamation projects, and mercury mining.

• We found that the first 75 years of European settlement in the Clear Lake Basin (including the most productive years of the SBMM) appeared to have barely detectable effects on mercury deposition. The large increase in mercury levels beginning in approximately 1927 corresponds to the use of heavy equipment to exploit the ore deposit at the SBMM with open pit methods. This finding provides managers and policymakers with further evidence in favor of regulating mining practices.

• Our data show that the nitrogen:phosphorous ratio in the sediments drops sharply after 1927, suggesting that nitrogen became more limiting relative to phosphorous, a condition that favors nitrogen-fixing cyanobacteria. This finding supports the oral history data that suggest that the lake became dominated by scum-forming cyanobacteria in the late 1920s or early 1930s.

• We helped show that sediment redox conditions play an extremely important role in the way stressors impact the Clear Lake system. Both the iron and phosphorous cycles are mediated by sediment surface redox conditions, and the core data demonstrate a major change in the sediment regime beginning in about 1927. Future basic and applied scientific work at Clear Lake will be driven by these results.

Supplemental Keywords:

ecosystem, ecosystem protection, environmental exposure and risk, geographic area, international cooperation, water, terrestrial ecosystems, aquatic ecosystem, aquatic ecosystem restoration, aquatic ecosystems and estuarine research, biochemistry, ecological effects, ecological indicators, ecological monitoring, ecology and ecosystems, environmental chemistry, restoration, state, water and watershed, watershed, watershed development, watershed land use, watershed management, watershed modeling, watershed restoration, watershed sustainability, agricultural watershed, exploratory research environmental biology, California, CA, Clear Lake, Lake Tahoe, anthropogenic effects, aquatic habitat, biogeochemical cycling, ecological assessment, ecology assessment models, ecosystem monitoring, ecosystem response, ecosystem stress, environmental stress, environmental stress indicators, fish habitat, hydrologic modeling, hydrology, integrated watershed model, lake ecosystems, lakes, land use, nutrient dynamics, nutrient flux, water management options, water quality, wetlands., RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Geographic Area, Water, Waste, Toxics, Aquatic Ecosystem, Restoration, Aquatic Ecosystems & Estuarine Research, Ecological Indicators, Environmental History, Engineering, Fate & Transport, West Coast, Ecosystem Protection, Aquatic Ecosystem Restoration, mercury transport, HAPS, Environmental Chemistry, 33/50, Ecosystem/Assessment/Indicators, Microbiology, Monitoring/Modeling, Geochemistry, Geology, Ecological Effects - Environmental Exposure & Risk, Environmental Engineering, mercury & mercury compounds, mining, lake ecosystem, sediment cores, Sulphur Bank Mercury Mine, ecosystem indicators, Clear Lake , Mercury Compounds, anthropogenic stresses, mercury loading, transport, aquatic ecosystems, nutrients, Clear Lake, anthropogenic stress, mercury

Relevant Websites:

http://ice.ucdavis.edu/cehr/ Exit

Progress and Final Reports:

Original Abstract

1997

1998

1999

Main 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