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: EERC - Center for Ecological Health Research (Cal Davis)
Center Director: Rolston, Dennis E.
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


This project seeks to use sediment cores as tools in reconstructing the history of anthropogenic stresses on aquatic ecosystems and their watersheds. The core work supplements other historical investigations of watershed processes in the Clear Lake area including analysis of long-term data sets, documentary sources, and reanalysis of curated specimens.

Signals deposited in sediment cores are extremely useful indicators of past processes within Clear Lake and other aquatic systems where deposition is relatively predictable. We have used relatively shallow sediment cores (200-300 cm deep) in Clear Lake to evaluate anthropogenic stressors that have affected this system over the past 200-300 yrs. The USGS raised some very deep cores (115m long, representing 450,000 years) during the 1970s and 80s for work on the long time scale, and the UC Davis Mercury Project raised some shallow cores (~1m, representing 50-75 years) during 1992 to investigate changes in sediment mercury since the last mining episode. In 1998 the investigators collected and analyzed 2-3 meter length cores, which reflect the last 200-300 years of changes in the lake in order to assess the kinds of natural and anthropogenic stresses applied at various time frames since European colonization. The initial hypothesis, derived from earlier historical work, was that the advent of heavy powered earthmoving equipment after W.W. I had multiple impacts on the lake and watershed. Open pit mining at Sulphur Bank, increased erosion due to road building and similar activities, and habitat destruction as a consequence of diking and filling activities were all made possible by the widespread use of this machinery beginning in the 1920s and early 1930s.


Some features of the five main cores raised in 1998 are consistent with this hypothesis. Many sediment parameters change suddenly and substantially at a time depth that dates to about 1927 (dated using 210Pb activity), when open pit mining at Sulphur Bank, modern road-building, and larger scale diking and filling projects began. Total mercury in the cores jumped by a factor of 10, sediments became drier, nitrogen and organic matter contents became lower. Professor Mount's group has also demonstrated large changes in magnetic properties at the same horizon. We have estimated the rate of dry matter deposition before and after 1927, assuming that a small uptick in total Hg concentration in the cores signals the beginning of Hg mining at Sulphur Bank in 1973. Only one of the cores shows an increase in dry matter accumulation rates after 1927 according to this calculation. Pending the analysis of a larger sample of cores, investigators tentatively conclude that the earthmoving hypothesis is false.

Investigators are currently investigating another hypothesis that may explain the changes in core characteristics after 1927. Acid mine drainage from Sulphur Bank carries large, but not yet accurately measured, amounts of sulfate and acidity into the lake. A conservative estimate suggests that acid mine drainage doubles to quadruples the sulfate loading to the lake. Sulfate concentrations dropped in the lake during the long drought of the late 1980s and early 1990s. At the same time, amounts of phosphorus cycling out of the sediments increased dramatically, while iron concentrations fell. Increased sulfate reduction in the sediments could well cause the changes we have observed in the sediments by increasing the amount of organic matter metabolized in the sediments. Sulfate diffuses to depths below which oxygen penetrates and hence supports oxidative microbial metabolism for some years after sediment burial. Chemical modeling work suggests that the sulfide produced as a byproduct of sulfate reduction may reduce iron recycling from sediments. Iron is the limiting nutrient in Clear Lake, and the drop in its concentration led to a succession of years with relatively clear water, abundant macrophytes, and relatively small cyanobacterial blooms. These conditions resemble the scanty scientific accounts of the pre-1930 period that describe the lake as having abundant bottom growth. They are also consistent with oral histories of long-time residents collected in the 1960s. Attempts to test directly if cyanobacteria were less abundant before 1927 using pigment analysis has not proven practical. Pigments are highly degraded and are not suitable for quantitative analysis of cyanobacteria specific pigments. Interestingly, although the lake's phosphorus cycling regime has returned to pre-drought levels, cyanobacterial abundance remains low and macrophyte biomass high. Uncertainty about the dynamics of iron cycling currently limits our understanding of cyanobacterial bloom dynamics.

Investigators have recently collected a new series of 250-300 cm deep cores (summer 2000), for several reasons. First, previous methyl mercury concentrations in buried core sections may not have been reported accurately because of an analytical artifact associated with the analytical procedure (distillation method) used to analyze for methyl mercury. This artifact problem has affected the entire scientific community throughout the world, but is especially problematic at Clear Lake because the high inorganic mercury content of the sediments enhances the analytical artifact. In fact, previously reported concentrations of methyl mercury in sediments may be as much as 95-98% artifact. Sediments from additional core sections will be analyzed for methyl mercury using (1) the older distillation method and (2) a method that has been determined to be more accurate (extraction method), especially for conditions in which there is high inorganic mercury present.

In addition to methyl mercury, investigators are also analyzing recent sediment cores for the following parameters: total mercury, arsenic, grain size, total sulfur, total phosphorus, phosphorus species, total carbon and total N, stable isotopes (delta13C, delta15N and delta34S) for estimating changes in algal communities over time), 210Pb (for dating shallow core sections to ca. 90 ybp), possibly 14C (for dating deep cores sections), and possibly pesticides (especially DDD, DDT and DDE) for evaluating the influence of the DDD additions to Clear Lake during the late 1940s and 1950s. The total mercury, methyl mercury and sulfur are especially critical to evaluate sulfate and mercury loading into Clear Lake from the Sulphur Bank Mercury Mine.

Expected Results:

The results of this research will have a major impact on how we monitor, study, and control anthropogenic stressors. For example, if local stressors are of dominant importance, technical resources and regulatory responsibility should perhaps be shifted towards smaller government units (cities and counties), whereas regional or super-regional commonalities suggest a relatively larger role for states and the federal government.

Supplemental Keywords:

Watershed, aquatic ecosystem restoration, Clear Lake, multiple stressors, anthropogenic stress, acid mine drainage, arsenic, sulfur, mercury., RFA, Scientific Discipline, Toxics, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, mercury transport, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, Geochemistry, HAPS, Restoration, Aquatic Ecosystem, Fate & Transport, Microbiology, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, Aquatic Ecosystem Restoration, Engineering, Geology, West Coast, 33/50, Environmental Engineering, Ecological Indicators, Environmental History, anthropogenic stresses, anthropogenic stress, mercury, Clear Lake , nutrients, mercury loading, Clear Lake, Sulphur Bank Mercury Mine, ecosystem indicators, mining, mercury & mercury compounds, aquatic ecosystems, Mercury Compounds, nutrient monitoring , lake ecosystem, sediment cores

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