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Final Report: Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
EPA Grant Number: R825433C029Subproject: this is subproject number 029 , 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: Watershed Response to Natural and Anthropogenic Stress: Lake Tahoe Nutrient Budget
Investigators: Reuter, John E. , Goldman, Charles R. , Heyvaert , Alan C. , Jassby, Alan D.
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:The objective of this research project was to develop a phosphorus (P) nutrient budget, and to establish a water-clarity total maximum daily load (TMDL) for Lake Tahoe.
Summary/Accomplishments (Outputs/Outcomes):With the recent discovery that P loading is a primary factor affecting algal growth in Lake Tahoe, it is now more important than ever to have a P nutrient budget that quantifies the critical sources and sinks of this nutrient. In the first part of our two-part research project, we identified five major sources of nutrients (including P and nitrogen [N]) to Lake Tahoe (direct wet and dry atmospheric deposition, stream discharge, direct overland runoff to the lake, groundwater, and shoreline erosion), and made preliminary estimates of P and N loading. These estimates suggest that approximately 14.4 MT, or about one-third of the total P load, is in the form of soluble P and immediately available for biological uptake. Values of this magnitude have been reported in the scientific literature.
Our results from this portion of the study clearly suggest the importance of direct runoff from urban areas. As restoration projects are being targeted and adaptive management proceeds, it will be very helpful to have more detailed data on the specific sources of nutrients within each of the major categories discussed above. Restoration should give priority to those areas that make the greatest contribution to the nutrient loading budget. This work helps set the stage for current efforts to establish a water-clarity TMDL for Lake Tahoe.
In the second part of this study, we used paleolimnological techniques (sediment profiles) to assess the effects of preanthropogenic perturbations, establish the natural baselines before these perturbations, and provide data on watershed and lake responses to anthropogenic stress. First, we established an accurate sediment chronology from 210Pb and 14C data. The 210Pb data indicated basin-wide changes in mass sedimentation rates over the last 130 years. High sedimentation rates were associated with clear-cut logging in the Lake Tahoe Basin from 1860-1900, followed by a threefold to fivefold decrease in mass sedimentation rates during the early twentieth century. These lower rates persisted until urbanization began in the basin after World War II.
Our results show that landscape recovery was rapid after clear-cut logging ended, and that sedimentation rates dropped to nearly predisturbance levels. The fact that mass sedimentation rates decreased shortly after the logging disturbance ended is testimony to rapid landscape stabilization with second growth forest. It also indicates that Comstock logging produced a pulse disturbance. By contrast, the disturbance from urbanization, and especially roads and other impervious surfaces, could persist as a chronic perturbation for a considerable amount of time. These data also suggest, however, that an effective mitigation of the watershed erosion caused by urbanization could directly improve water quality over a time period on the order of 10-20 years.
The following activities were accomplished:
• Research at Lake Tahoe has demonstrated a shift from frequent stimulation of algal growth by N to primarily P stimulation. Excessive atmospheric deposition of atmospheric N is considered responsible for this shift in nutrient stimulation. Because P is typically transported along with sediment, these findings underscore the importance of sediment control, erosion mitigation, acquisition of sensitive lands, treatment of surface runoff, and other means of restoration. Prioritization of restoration projects depends on identifying critical nutrient sources.
• We have identified five major categories of external nutrient loading to Lake Tahoe: (1) direct atmospheric deposition and precipitation; (2) stream discharge; (3) overland runoff directly to the lake; (4) groundwater; and (5) shoreline erosion. The major losses include the settling of material from the water column to the bottom and, to a much lesser extent, discharge to the Truckee River. P and N loading, expressed as metric tons per year, largely were determined using long-term data collected as part of the Lake Tahoe Interagency Monitoring Program. Estimates of loading from surface runoff directly to the lake are not extensive; therefore, results for this category must be viewed as preliminary. By focusing on these five areas, we can help pinpoint those areas that are most in need of nutrient loading mitigation efforts. Our findings will help management agencies prioritize restoration projects.
• We estimate annual loading of total P to Lake Tahoe at approximately 44 metric tons. Direct runoff, stream loading, and atmospheric deposition account for approximately 25-30 percent each. This information suggests that the three important sources of P should be evaluated in more detail to determine the specific sources of P within each category, and to evaluate the cost-benefit ratio for P reduction within each category. With better loading estimates, management efforts can more efficiently and cost effectively target the most insidious sources of P loading.
• Our estimates suggest that approximately 15 MT or about 30-35 percent of the total P load is in the soluble P form. Soluble P is much more immediately bioavailable. Therefore, soluble P is considered critical for management purposes. Values for soluble P contribution of this magnitude are not uncommon in the scientific literature.
• Independent analysis of material contained in a vertical series of sediment traps deployed in Lake Tahoe shows that nutrient sedimentation losses to the bottom of Lake Tahoe are 402 MT for total N and 53 MT for total P. These measured values agree remarkably well with the independent loading estimates given above. Loss of P and N via the lake's only outflow is minimal. This close agreement gives us increased confidence that the loading rates are representative.
• Analysis of mass sedimentation rates from sediment cores taken from the deep portion of Lake Tahoe showed an uneven flux of material to the bottom since the mid-1800s. This suggests that models using constant sedimentation rates may not be entirely applicable to lakes with significant historic periods of perturbation. The average mass sedimentation rate during the period 1900-1970 was nearly identical to baseline values, with a clear signal for the onset on cultural eutrophication.
• Our paleolimnologic studies on sediment cores suggest that an effective mitigation of the watershed erosion caused by urbanization could improve directly water quality over a time period on the order of 10-20 years. The fact that mass sedimentation rates, including biogenic silica (acting as a surrogate for algal growth), decreased shortly after the Comstock logging disturbance in the late 1800s points to a rapid landscape stabilization with second growth forest. This was, however, an acute, albeit severe, disturbance. By contrast, the disturbance from urbanization, and especially roads and other impervious surfaces, could persist as a chronic perturbation for considerable time. This speaks to the requirement for effective and sufficient numbers of erosion control projects.
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. , Ecosystem Protection/Environmental Exposure & Risk, Water, INTERNATIONAL COOPERATION, Scientific Discipline, RFA, ECOSYSTEMS, Water & Watershed, Restoration, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Aquatic Ecosystem, Biochemistry, Environmental Microbiology, Watersheds, Ecology and Ecosystems, ecological impact, watershed management, watershed restoration, ecological research, ecology assessment models, aquatic habitat protection , land use, wetland restoration, Lake Tahoe, contaminant exposure, anthropogenic processes, aquatic ecosystems, environmental stress, watershed sustainablility, hydrology, nutrients, restoration strategies, ecosystem stress, biodiversity
Relevant Websites:
Progress and Final Reports:
1999 Progress Report
2000 Progress Report
Original Abstract
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