Grantee Research Project Results

Final Report: Role of Hydrogeologic Processes in Alpine Ecosystem Health

EPA Grant Number: R825433C049
Subproject: this is subproject number 049 , 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: Role of Hydrogeologic Processes in Alpine Ecosystem Health
Investigators: Fogg, Graham
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:

Past hydrologic studies of the Tahoe Basin have tended to neglect groundwater processes, more because of a lack of data than a lack of knowledge of the role of groundwater in the basin. The objectives of this research project were to: (1) investigate the interaction between the lake and groundwater through a detailed analysis of Pope Marsh; and (2) develop a substantially improved water budget for the lake, including estimates of actual groundwater contributions and losses from the lake, rather than simply treating groundwater as the residual in the budget. These studies represent key components in a necessary scientific basis for managing groundwater to minimize impacts on the wetlands and the lake.

Summary/Accomplishments (Outputs/Outcomes):

We completed a comprehensive hydrogeologic characterization of Pope Marsh in the Tahoe Basin. Monitoring of both groundwater and surface water levels, as well as groundwater chemical composition, led to important findings regarding anthropogenic stresses on the marsh. Our detailed measurements and analyses of surface and groundwater fluxes indicate that groundwater inflow to the marsh is a significant component of the water budget.

Overall, we suggest that human activities outside of the marsh (e.g., groundwater pumping, development, and management of lake water levels) impact the hydrology within the marsh. These hydrologic changes increased the marsh's sensitivity to naturally occurring stresses, resulting in rapid changes in species distribution. The results also demonstrate linkages between the hydrology of the marsh, peat development, and species distribution. Therefore, changes in the anthropogenic stresses on Pope Marsh likely will initiate gradual changes in the community composition of the marsh, which could dramatically change the effectiveness of the marsh as a filter of nutrients and sediments.

In the second portion of our project, we evaluated the Lake Tahoe water budget, and we updated and improved the estimated water budget through the incorporation of recent evaporation estimates and an analysis of archives of precipitation, runoff, and water production data. In evaluating the water budget of Lake Tahoe, perhaps the largest source of systematic uncertainty has been in estimates of evaporation from the lake surface. We demonstrated that measurements of evaporation made during the past 100 years near the Lake Tahoe outlet dam at Tahoe City are unreliable because of varying shelter from sun and wind exposure provided by nearby brush and trees, and we provide the first reliable estimates.

The following activities were accomplished:

• We found peat deposits in Pope Marsh that date to 2,300 years before present. Because peat deposits require saturated conditions for preservation, this finding indicates that groundwater and/or surface water was discharging into (i.e., sustaining) the marsh during the same time period, although natural elevation of Lake Tahoe (pre-1874) was significantly lower than it is today.

• Computer modeling and field observations show that, with the current hydrologic budget of the marsh, the marsh could not have remained saturated before 1874 because of the lower lake levels before the construction of the dam at the outlet of Lake Tahoe. Therefore, additional natural inflows to Pope Marsh must have existed in the past.

• The most likely changes that caused the loss of inflow into Pope Marsh are the construction of the Tahoe Keys and groundwater pumping. Construction of the Tahoe Keys apparently diverted away from the marsh the flow from the Upper Truckee that had sustained plant communities during dry summer months. Groundwater pumping diverts groundwater away from the marsh and induces subsurface water flow from Lake Tahoe to the marsh. This finding and the previous two findings are useful to: (1) Tahoe Basin resource managers for determining what land and water management strategies may help or harm the wetlands; and (2) environmental scientists concerned with wetlands characterization and nutrient management strategies.

• Our correlations between the rate of upward groundwater flow and peat development in the southwest area of the marsh corroborate other researchers' findings, indicating that peat mound development may be controlled by environmental or hydrogeologic factors, and that the local hydrology can control the natural development and sustenance of a wetland. This finding is a scientific contribution to wetland science, on which wetland management must be based.

• Our carefully executed measurements show that annual evaporation from the lake is approximately 35 in. Before this project, no reliable estimates of Lake Tahoe evaporation, the largest term in the entire water budget, were available. This information is fundamental to any hydrologic analysis or management strategy for the basin.

• We updated and improved the estimated water budget of Lake Tahoe. We included a statistical analysis of errors through the incorporation of recent evaporation estimates and an analysis of archives of precipitation, runoff, and water production data.

• Our results suggest that the magnitude of deep, low-frequency (many years) net groundwater flow into Lake Tahoe is small. Nevertheless, it is possible that portions of the lake are losing significant volumes of water to the groundwater system, although other portions are gaining from groundwater. This is important and useful to resource managers who are concerned with the long-term impacts of anthropogenic or natural perturbations to the Tahoe Basin hydrologic cycle.

 

Figure 1. Summary of the Lake Tahoe Water Budget. Total annual inflow (average) = total annual outflow (average) = 650,000 acre-feet.

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, Waste, Aquatic Ecosystems & Estuarine Research, Ecological Risk Assessment, Fate & Transport, State, West Coast, Ecology, Regional/Scaling, Monitoring/Modeling, Hydrology, Ecology and Ecosystems, regional hydrologic modeling, California (CA), ecosystem health, hydrologic processes, analytical models, Lake Tahoe, aquatic ecosystem, ecological models, environmental monitoring, Sierra Nevada Mountains, modeling ecosystems, environmental stress, Sierra Nevada, hydrologic modeling, transport, modeling, aquatic ecosystems

Progress and Final Reports:

Original Abstract

1997

1998

1999 Progress Report

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