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1999 Progress Report: Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
EPA Grant Number: R825433C034Subproject: this is subproject number 034 , 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: Regional Hydrogeology and Contaminant Transport in a Sierra Nevada Ecosystem
Investigators: Fogg, Graham
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:To define the hydrogeologic processes affecting alpine ecosystem function, focusing on the Tahoe Basin in the Sierra Nevada Mountain Range.
Progress Summary:Large uncertainties regarding the groundwater component of the Tahoe Basin water budget have confounded the characterization of water circulation in the system. For example, knowledge of the hydrology has been inadequate to determine whether groundwater interaction with Lake Tahoe results in a net loss or gain in water to the Lake. In our studies we have set out to (1) evaluate the Lake Tahoe water budget, and evaluate approaches to further constrain the water budget of the Tahoe Basin, (2) evaluate evaporation measurements that have been performed for Lake Tahoe and obtain more accurate evaporation estimates, and (3) characterize regional hydrogeologic processes affecting groundwater circulation.
Water budget estimates, based on published literature and reports, were performed for Lake Tahoe, for the Tahoe Basin watershed land surface, and for the Tahoe Basin as a whole (watershed land surface plus Lake Tahoe). For each water balance method, the groundwater component was estimated as a residual. A groundwater component estimate was also made using Darcy's equation for the Tahoe Basin aquifers adjacent to Lake Tahoe. A major focus of the analysis was to estimate the uncertainty in each water budget component estimate.
Calculations based on Darcy's equation, estimates of groundwater flow into Lake Tahoe (neglecting pumping) ranged from about 7,000 to 200,000 ac-ft/yr. A water balance calculation for the Tahoe watershed land surface yielded a residual groundwater component ranging from 0 to about 200,000 ac-ft/yr. A water balance on Lake Tahoe yielded a groundwater residual ranging from negative values (i.e. Lake Tahoe as a net groundwater-losing lake) to about 66,000 ac-ft/yr. Thus, an upper bound of around 66,000 ac-ft/yr of groundwater flow into Lake Tahoe is estimated, corresponding to about 10% of the annual precipitation on the watershed land surface. This estimate will be revised when improved estimates of the evaporation component are obtained, as discussed below.
It appears that no reliable, long-term measurements of evaporation exist for Lake Tahoe. Long-term evaporation pan data exist for a site at Tahoe City; however, unchecked forest growth at this site has caused almost total shading of the pan, invalidating most of the data. The trees shade the pan for about half or more of the daylight hours, and provide some shelter to the pan from wind.
Improved measurements of Lake Tahoe evaporation rate are being pursued. In addition to setting up our own evaporation pan in the basin, we are collaborating with the Desert Research Institute in obtaining eddy correlation measurements of evaporation.
As mentioned above, based on published estimates of water budget components for Lake Tahoe, with ground water flow as a residual, there is an indication that Lake Tahoe may be a net groundwater-losing lake. The possibility of substantial underflow (groundwater flow in the streambed alluvium) beneath the Lower Truckee River, in the vicinity of the Lake Tahoe dam, was been evaluated. Such flow is unlikely, based on data archived from two stream gages on the Lower Truckee. Thus, we cannot yet rule out the possibility of groundwater exiting the basin via another mechanism, such as flow under the Carson Range at the eastern margin of the basin. The possibility of eastward groundwater flow beneath the Carson Range is suggested by the substantial hydraulic head differential (460 m) and head gradient (approximately 4%) between Lake Tahoe and adjoining valleys flanking the eastern margin of the Carson Range. Modeling of this potential groundwater flow path is currently underway, and incorporates the mutual interactions of groundwater flow and heat flow.
Future Activities:We are collaborating with the Desert Research Institute in obtaining improved estimates of Lake Tahoe evaporation rate. Eddy correlation measurements should provide an accurate measurement of evaporation rate, and allow more reliable correlations to be made between pan evaporation and Lake Tahoe evaporation.
Ongoing research suggests that energy budget and deuterium mass balance techniques can be used to better estimate the Lake Tahoe water budget. Published data on deuterium levels and on energy budget components for Lake Tahoe can be combined with monthly humidity data for air in the Tahoe Basin, resulting in two additional constraints on the Lake Tahoe water budget. Currently, archives of humidity data pertaining to the Tahoe Basin are being sought, and will be analyzed, evaluated, and used in this approach.
To investigate possible deep groundwater flow from within the Tahoe Basin underneath the Carson Range and into the Carson, Eagle, and Washoe valleys, pertinent published isotopic, geochemical, and geological evidence will be evaluated. Analysis and numerical modeling of deep groundwater flow, including the interaction of heat flow and groundwater flow, will be completed. Heat flow information and processes will help constrain uncertainty of the groundwater model while elucidating origin and function of hot springs, which occur throughout the Sierra Nevada ecosystem.
As discussed in last year's report, MTBE was found at high levels near most leaking underground fuel tank (LUFT) sites in the Tahoe Basin. Additionally, the presence of low levels of MTBE in Pope Marsh groundwater indicates that pollutants from the lake may be transported into the marsh via groundwater. MTBE represents the only known, widespread groundwater contaminant in the Tahoe Basin. Ultimate impacts of this contaminant on quality of groundwater, surface water, as well as ecosystem function has yet to be evaluated. Monitoring data for pollutants such as MTBE is being collected at numerous LUFT and other sites, and is available for investigation of transport and fate of contaminants in specific areas of the Tahoe Basin. Such data will be combined with regional hydrogeological data in a quantitative analysis of long-term impacts of MTBE on basin water quality and, in turn, Lake and wetland water quality.
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, Water, INTERNATIONAL COOPERATION, Scientific Discipline, Waste, RFA, ECOSYSTEMS, Remediation, Water & Watershed, Restoration, Aquatic Ecosystem Restoration, Aquatic Ecosystems & Estuarine Research, Terrestrial Ecosystems, Aquatic Ecosystem, Biochemistry, Environmental Microbiology, Fate & Transport, Watersheds, Ecology and Ecosystems, ecological impact, contaminant transport models, fate and transport, geochemistry, watershed management, watershed restoration, ecological research, ecology assessment models, MTBE, aquifer fate and treatment, aquatic habitat protection , groundwater, land use, wetland restoration, Lake Tahoe, hydrologic processes, contaminant exposure, contaminant biodegradation rates, aquatic ecosystems, environmental stress, biogeochemical study, watershed sustainablility, contaminated groundwater, hydrology, Sierra Nevada, restoration strategies, ecosystem stress, biodiversity, biogeochemical cycling, integrated watershed model
Progress and Final Reports:
Original Abstract
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