Grantee Research Project Results

2000 Progress Report: Water Motions and Material Transport

EPA Grant Number: R825433C017
Subproject: this is subproject number 017 , 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: Water Motions and Material Transport
Investigators: Schladow, S. G.
Institution: University of California - Davis
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 2000
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
RFA: Exploratory Environmental Research Centers (1992) RFA Text |  Recipients Lists
Research Category: Center for Ecological Health Research , Targeted Research

Objective:

To understand the physical processes of water circulation, transport and mixing in Clear Lake, specifically in the Oaks arm of Clear Lake close to the main source of mercury, the Herman Pit.

Progress Summary:

Since the very beginning of the research the physical processes of circulation and mixing in Clear Lake displayed a high degree of spatial and temporal variability. An integrated approach combining the analysis of 3-D model results and field observations was followed to provide a solid description of the spatial and temporal structure of lake hydrodynamic processes.

Given the lack of an appropriate computational tool, the first objective in the research was to construct a comprehensive, efficient and accurate three-dimensional model that could be used to improve our understanding of the circulation in Clear Lake. The availability of a relatively large number of three-dimensional flow solvers, suggested at the outset that there was a greater need for formulating a methodology by which such codes could be evaluated, rather than the development of a new code. To this end, both a finite difference and a finite element flow solvers were used to develop this methodology, and then compared for their suitability for applications in lakes. A 3-D semi-implicit leapfrog-trapezoidal finite difference solver (SI3D) was selected on the basis of the results of the test problems to constitute the skeleton of the hydrodynamic lake model. The original solver was extensively modified to incorporate features needed for the accurate simulation of lake hydrodynamic phenomena. The new model has been termed SI3D-L.

In May 1999 we conducted the first experiment in which currents, water temperatures, wind and other meteorological variables were extensively and simultaneously monitored. A total of six meteorological stations were concentrated in the Oaks Arm and the Lower Arm during May to help characterizing the wind field over Clear Lake. The records of those stations together with those of other operative stations were used in the construction of continuous maps of wind by means of multiquadric interpolation schemes. The analysis of the wind fields shows a wind field with an extraordinary rich structure shaped by the surrounding topography. The spatial variability turned out to play an important role in generating the large-scale circulation in Clear Lake.

The model results and the observations collected during the course of two field experiments (in 1997 and 1999), have allowed us to build a sound description of the circulation in the Oaks arm. The dynamics in the Oaks arm is characterized by a marked diurnal periodicity dictated by the wind regime. The typically northwesterly wind encounters a lake that due to the surface heat flux during the morning and early afternoon hours is stratified. The wind acts during the afternoon and evening hours on this weakly stratified system to generate horizontal temperature gradients both along and across the longitudinal axis of the Oaks arm. During night and early morning hours, when the wind forcing is negligible, the baroclinic pressure gradients that result from the horizontal differences in temperature become the dominant forcing mechanism in the system driving currents of up to 10-15 cm/s, westward at the surface and eastward at the bottom. This cycle of setup and relaxation of horizontal temperature gradients repeats in the stratified lake with a diurnal periodicity that is dictated by the wind regime. The setup and relaxation processes are modulated by the influence of the earth's rotation and creates a residual circulation. This mechanism of circulation has been termed wind baroclinic pumping, or simply baroclinic pumping. The cyclonic residual circulation that results is superimposed on the direct wind driven circulation, also of cyclonic nature, enhancing the rates of transport and facilitating the migration of mercury laden particles to the other two arms of the lake.

The exchange among the three basins of Clear Lake was investigated using 3-D particle tracking routines and numerical passive tracer releases. Those techniques also proved adequate to visualize the baroclinic pumping mechanism driving the internal circulation in the Oaks arm. Clouds of particles and gaussian plumes of passive tracers were released at several locations across the Oaks arm and tracked in the model for several days. The numerical results indicate that during non-stratified conditions the circulation in the Oaks arm is such that very little exchange of particles exists with the other two basins. Under stratified conditions, however, the rate of transport is enhanced and the connection among the three arms of the lake is fairly active. Any contaminant released in the Oaks arm would reach the other two basins in about 3-7 days. The contaminant would penetrate into the Lower arm following the surface currents or into the Upper arm mainly through the bottom currents.

The observations, and particularly the numerical simulations, revealed that Clear Lake is a very active system that changes dramatically in response to the diurnal wind events. Because of the changing nature of the hydrodynamics of Clear Lake, observations gathered at a given moment in time may not be representative of the state of the lake 12 hours later. The lake hydrodynamics is also spatially variable, and the conditions at a given sampling station will not be representative of the existing conditions only 1000 meters apart. Basing any interpretation of field experiments on partial observations could leave to wrong answers. Given the impossibility to sample both at the right spatial and temporal scales of change of active systems such as Clear Lake, 3-D models should be employed to feel the gaps in the observational data. SI3D-L has been proven here to be an invaluable tool in the identification of the key transport processes in Oaks arm, house of the Sulphur Bank Mine.

Supplemental Keywords:

RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, Waste, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Water & Watershed, Aquatic Ecosystems & Estuarine Research, Restoration, Aquatic Ecosystem, Fate & Transport, Environmental Microbiology, Monitoring/Modeling, Terrestrial Ecosystems, Biochemistry, Environmental Monitoring, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Watersheds, fate and transport, watershed management, water circulation, sediment transport, restoration strategies, Clear Lake, watershed influences, hydrology, wetland restoration, integrated watershed model, aquatic ecosystems, environmental stress, source load modeling, watershed sustainablility, material transport, ecosystem stress, ecology assessment models, ecological impact, aquatic habitat protection , ecological research

Progress and Final Reports:

Original Abstract

1997

1998

1999

Final 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