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1996 Progress Report: Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
EPA Grant Number: R825433C001Subproject: this is subproject number 001 , 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: Potential for Long-Term Degradation of Wetland Water Quality Due to Natural Discharge of Polluted Groundwater
Investigators: Fogg, Graham , Marino, Miguel
Institution: University of California - Davis
EPA Project Officer: Levinson, Barbara
Project Period: June 30, 1995 through January 1, 2000
Project Period Covered by this Report: June 30, 1995 through January 1, 1996
Project Amount: Refer to main center abstract for funding details.
RFA: Exploratory Environmental Research Centers (1992)
Research Category: Center for Ecological Health Research , Targeted Research
Description:
Objective:This project has become two separate projects and the results are reported separately.
IV.1a Role of Hydrogeologic Processes in Wetland Health - Graham Fogg
The goal of this investigation is to assess the role of hydrologic processes (recharge, discharge, chemical transport) in wetland health by (1) identifying sources of hydrologic stress in a marsh, (2) identifying the processes that deliver the stress from the hydrologic cycle to the marsh ecosystem, and (3) determining how these processes interconnect and are influenced by one another.
In evaluating the health of ecological systems, one must consider multiple indicators of stress. These indicators include changes in nutrient cycling, changes in productivity, retrogression to short lived, opportunistic species, and a reduction in the success of the dominant biota. These indicators may be applied to marshes in the South Lake Tahoe basin to evaluate the extent of stresses. (See section C.3)
Pope Marsh, South Lake Tahoe, shows signs of severe stress, such as the die-off of large areas of hydrophytes, and the nearly complete elimination of Scirpus from the marsh. In addition, opportunistic species of Hipporus have undergone a population explosion. Evidence of abnormal hydrology suggests that anthropogenic influences may contribute to declining the health of the Marsh. Groundwater pumping influences the hydrology of Pope Marsh, and causes seasonal reversals in flow direction. An understanding of the wetland hydrology is critical in determining the origin of stresses in a wetland. Researchers have proposed hypotheses regarding the links between groundwater recharge, discharge, chemistry, peat development, and species diversity; however, most of these hypotheses remain untested in different types of wetlands.
Disruption of the groundwater system may result in reduction or elimination of sensitive species. A few researchers have begun to examine these effects on the health of wetland systems, but no similar studies have been completed in the Tahoe Basin. This study will identify the anthropogenic and natural hydrogeologic stresses impacting Pope Marsh, and similar wetlands in the Tahoe Basin.
In the Tahoe Basin, the health of existing wetlands is paramount. (See section IV.0) Reduced lake water clarity has resulted from excessive input of nitrogen, iron, and phosphorus. Wetlands have been recognized as an important means of mitigating adverse impacts of these solutes in the lake. Furthermore, the disruption of wetlands in the Tahoe Basin could have additional impacts beyond the release of nutrients to the lake. A study of uranium deposits in the Carson Range-Lake Tahoe area found that two small fens on the south east shore of Lake Tahoe contain up to 0.6% uranium, or approximately 40,000 kg. The disruption of wetlands could increase redox potential and pH, which can increase the solubility of uranium by several orders of magnitude, resulting in the release of uranium to ground and surface waters.
Current Status:
To date we have completed an initial hydrogeologic characterization of Pope March in the Tahoe Basin. This consisted of the installation of I I piezometers in four clusters, two water surface gauges, and 42 soil borings. Soil borings were located to coincide with species transects completed by fellow Center investigators Harry Spanglet and Dr. Rejmankova. All soil borings and piezometers were surveyed for elevation. Locations of installations and wetland features were mapped using a Global Positioning System.
Groundwater and surface water analyses revealed chemical trends within the marsh. Two distinct categories of shallow groundwater exist, differentiated by chloride concentration. In addition, concentrations of iron, silica, ammonium, nitrate, and sulfate vary with location and depth. Additional sampling locations will be necessary to determine whether the nutrient and major ion gradients within the marsh will correlate with manifestations of stresses in the marsh.
The piezometer clusters and surface water gauges allowed measurement of water table elevations and three-dimensional driving forces for groundwater flow. This information indicated a seasonal reversal in gradient between the lake and the marsh. Between July and November, 1995, the most productive time period in the marsh, water flowed from the lake inland. Beginning in November, 1996 groundwater flowed from the marsh into Lake Tahoe. This oscillation of gradient may have major impacts upon the health of the wetland, and the transport of nutrients between the wetland and the lake.
Surface water flows in Pope Marsh corroborated the groundwater indications of flow reversals. In September, October, and November, water levels in the Marsh dropped to a low enough level that the north and south portions of the marsh were joined by a narrow channel. The channel flowed inland, from north to south, discharging as much as 322 m3 /day. Accordingly, our water table maps show that a groundwater sink may cause the inland flow during the summer and fall months. This sink correlates with pumping from a nearby water supply well, a correlation that strongly suggests groundwater pumping may cause the sink. Uneven evapotranspiration may also play a role. Intensive monitoring in the spring months will help to discern the effects of pumping and evapotranspiration. Additional evidence for pumping effects includes diurnal fluctuations in groundwater levels. At Pope Marsh, the fluctuations do not correlate with barometric or earth tides. Therefore, they likely originate from pumping influences.
Statistical correlation was used to identify some of the detailed aspects of hydrogeology that affect the vitality of Pope Marsh. The analysis focused on peat formation, because the unusual hydrologic attributes of peat make it a major factor in the resistance of wetlands to hydrologic stresses, and other researchers have proposed that peat development is closely tied with groundwater now. It has been suggested that, in peatlands of the eastern and midwestern U.S., low relief groundwater discharge areas develop greater thicknesses of peat. A statistical correlation of peat thickness to paleo-topography in Pope Marsh is consistent with this model of development. Soil borings and surveys allowed measurement of inorganic and organic sedimentary features. The top of the inorganic sediments represents the original ground surface, and this surface defines paleo-topography. Linear regression analysis of peat thickness versus paleo-topography showed that a statistically significant relationship exists between the original ground surface and the degree of peat development in Pope Marsh.
More work will be necessary to refine the model of paleo-topographic control of peat distribution, and to tie the distribution of peat in with the health of the wetland. Based on previous work and on observations in Pope Marsh, we hypothesize that areas of disturbed vegetation will demonstrate positive correlations with 1) hydrologic stresses, and 2) thinner or degraded peat. In addition, we suspect that paleo-topography influences peat development via hydrologic influences, and we expect that peat thickness will also correlate with hydrologic function.
Future Plans:
This project will continue the investigation of sources and mechanisms of stress in Pope Marsh. This will include: (1) installation of additional piezometer clusters along transects intersecting stressed or dying vegetation, or areas where vegetation changes have been noted, (2) installation of deep piezometers using hollow stem auger drilling, (3) installation of seepage meters to determine vertical surface water flux in the vicinity of the groundwater sink, (4) mapping of species distribution in cooperation with fellow Center investigators Dr. Rejmankova and Harry Spanglet, (5) conversion of aerial photographs to GIS format to track changes in plant species distribution, (6) permeability testing at all piezometers to determine the hydrologic characteristics of strata, and (7) continued and intensified monitoring of chemistry and water table elevations.
Similar hydrogeologic characterization efforts will also be directed at one or more higher altitude wetlands currently being studied by Dr. Rejmankova's group. These wetlands are not impacted by lake level fluctuations and groundwater pumpage from wells and will therefore provide a useful comparative analysis on subsurface controls on wetland health, particularly the role of water table fluctuations and groundwater recharge/discharge mechanisms. The physical and basic chemical hydrogeologic characterization will be complemented by analysis of stable isotopic composition of the subsurface waters and, resources permitting, groundwater age dating. Results of these characterization and monitoring efforts will be used in the construction of conceptual-numerical models of the circulation of water and solutes in the coupled groundwater-wetland ecosystem. This analysis will elucidate interconnections between anthropogenic and climatic effects on groundwater flow, and processes which deliver these stresses to the wetland habitat. This information is critical for understanding the role of the groundwater system, Pope Marsh, and other marsh areas in ecosystem-health of the Tahoe Basin and the Sierra Nevada.
IV.lb Pesticide Transport in the Vadose Zone and Groundwater - Miguel Marino
The goals of this project are as follows:
To develop a systematic procedure, applicable at the regional scale, for the assessment of: (a) the leaching potential of a pesticide to groundwater in agricultural areas, and (b) the potential threat of pesticides emissions to groundwater on exposure levels in aquifers and groundwater discharged to wetlands and rivers.
Refinement of the regional-scale assessment procedure in favor of less data requirement, and increasing the confidence in the absolute level of predictions of leached pesticide concentrations below the crop-root zone, intermediate vadose zone, and groundwater.
To provide the Sacramento River Watershed project with long-term predictions of pesticides exposure levels in ground water and groundwater discharged to selected sites that are most vulnerable to agricultural stresses. The information (i.e., pesticides exposure levels) can be used to evaluate and predict the effect of biological stressor, such as pesticides, on the Sacramento River watershed.
To develop optimal criteria aimed at protecting sites in the Sacramento River Watershed that show alarming long-term predictions of pesticides exposure levels. The recommended preventive measures will be based on regulating agricultural practices and using lateral and horizontal protection zones.
Leaching of pesticides to groundwater is an important environmental aspect of ecosystem health because ground water ultimately discharges to wetlands. Pesticides are one class of agricultural chemical inputs which are sources of groundwater contamination. Because agricultural practices constitute a significant stressor to the Sacramento River watershed, and because recent studies have detected pesticides exposure levels exceeding National Academy of Science recommendation, it is paramount to the central goal of the Center to develop a methodology to predict, with reliability, exposure levels of pesticides in groundwater and groundwater discharged to river ecosystems.
Pesticide leaching potential is largely based on a combination of mobility and transformations properties. These two properties are influenced by physical, (bio)chemical, and physiological processes such as infiltration (rainfall and irrigation water), evapotranspiration, root uptake, advection, adsorption, first-order transformation, volatilization, dispersion, and inter-layer mass transfer (i.e., matrix diffusion). They are also influenced by the geometric and hydraulic properties of the soils and aquifers (i.e., hydrogeology). Hence, understanding of the interaction between the different processes and modeling them at the local and regional scale is an important step toward conducting risk assessment against pollutant exposure levels in the neighborhood of supply wells and streams and wetlands that are interacting with or sustained by groundwater discharge.
The approach is to develop improved methods of modeling solute transport along pathways originating from the ground source to groundwater and discharge areas, and applying these methods in assessing the threat of regional groundwater contamination to the Sacramento River watershed. Specifically, the following points are emphasized: (1) averaged description of fate and transport in the root and intermediate vadose zones, (2) the effect of uncertainty in net groundwater recharge and (bio)chemical parameters, on pesticides levels in ground water and loading at groundwater discharge areas (streams and wetlands), and (3) developing indices that screen pesticides with respect to their long-term potential to migrate past a given zone in the aquifer and contaminate adjacent ecosystems.
Current Status:
To date, working in concert with Graham Fogg, new numerical and analytical methods for probabilistically quantifying origins and ages of ground waters arriving at discharge points (e.g., wetlands, wells) have been developed that rigorously account for the physical processes involved in pollutant transfer between different geologic materials. Results indicate that currently observed deterioration in groundwater quality in a typical alluvial groundwater basin is due to land use practices in the late 1940's and 1950's and that the deterioration may continue for many decades, thereby eventually impacting any wetlands and streams that are sustained by groundwater discharge. By the end of the current fiscal year, we anticipate having estimates of expected maximum dose of conservative contaminants such as nitrates and agricultural salinity to the Sacramento River and Delta System Wetlands. This is being accomplished by application of our Previously developed analytical stochastic model. Effects of simplifying assumptions in this model are being tested via local-scale numerical simulation experiments using our newly developed numerical modeling algorithm for transport in complex geological media.
Through previous research funded by the EPA Center, the investigators have developed two-dimensional and coupled transport models in layered porous formations. Two-dimensional analytical solutions are obtained which describe on average basis the diffusional mass transfer across a stratum and the capacitance effect of low permeability layers such as clay and silt to store and release solutes. The developed results are of basic and applied nature; they augment current literature and provide more insight into the role of heterogeneity of layered formations, such as aquifers of fluvial origin, on hydrodynamic dispersion of contaminant plumes in groundwater. The nature of the results is of particular significance to risk assessment against pollutant exposure levels in subsurface water and ecosystems such as streams, lakes, and wetlands that are interacting with or sustained by groundwater discharge. Furthermore, the results are not site specific and can be applied to risk assessment and remediation studies insofar as the assumptions are not violated. Application of the theory to Borden aquifer (Ontario, Canada) data from a natural gradient experiment of tracer chloride was satisfactory and promising toward evaluating the threat of regional groundwater contamination to the Sacramento River. Much work is needed to supplement the basic findings in this area, especially when moving from the local field scale to the regional scale, where uncertainties due to larger-scale heterogeneity play a dominant role in describing the spreading of contaminant plumes and their migration toward the ecosystems.
Efforts have been initiated to develop models to link the chemical source at the surface to groundwater. The models take into account processes such as advection, crop uptake, adsorption, biochemical degradation, and volatilization. The soil transport models will be linked to models being developed under Project IV.3 and to two-dimensional groundwater transport models, and analytical solutions will be obtained. It is anticipated that crop uptake, volatilization from soil surface, and agricultural practices may have profound effects on the long-term predictions of pesticides exposure levels in groundwater discharge areas. Further investigation is needed to assess the impact of uncertainty in data, such as precipitation. the interaction among the different physical and (bio)chemical processes, and agricultural practices on exposure levels in the Sacramento River.
Future Plans:
Develop lumped-parameters transport models to link the chemical source at the surface to groundwater. The models will consider averaged concentrations in the root zone and the intermediate vadose zone. The models will take into account processes such as advection, evapotranspiration, adsorption, first-order (bio)chemical transformation, root-uptake, and volatilization. While taking into account the major transport and fate processes, the models neither require extensive data nor are computationally demanding.
Develop simple screening indices for assessing the long-term and relative potential of selected pesticides to contaminate groundwater discharge areas at the Sacramento watersheds. The indices are developed by integrating the soil and groundwater models in time, and they are designed for long-term assessment based on annually-averaged input variables. The proposed indices will take into account additional factors such as crop uptake, volatilization from soil surface, agricultural practices, and properties of the subsurface environment (hydrogeology). The indices can be applied for risk assessment in ecosystems elsewhere.
Use the methodology to assess the effect of temporal variability of net groundwater recharge and spatial variability of (bio)chemical parameters on both estimates of pesticides leaching potential and the uncertainties associated with those estimates (i.e., probabilistic risk assessment). Probabilities of exceedance of maximum levels of concentrations, which are set by the EPA, will be obtained in space and time.
For cost-effective application of the methodology to the Sacramento River watershed, the methodology will be applied to agricultural fields bordering the Sacramento River and upper portions of the San Joaquin Rivers, and their Delta. Necessary data will be obtained from the U.S. Geological Survey (groundwater levels, soil type, and land use), the California Department of Pesticide Regulation (application history of pesticides), the USDA Soil Conservation Service (moisture content), and Earth Sciences Library, University of California at Berkeley (meteorological CD ROM data base). The data, along with the chemical properties of the pesticides, will be used in the developed fate and transport models to construct regional plots for risk assessment, using Monte Carlo simulations. The planar plots determine dynamic probabilities of exceeding maximum exposure levels in groundwater and groundwater discharge areas to the Sacramento River and upper portions of San Joaquin Rivers.
Develop optimal criteria for designing groundwater protection zones and regulating agricultural practices aimed at protecting most vulnerable groundwater discharge areas at the investigated ecosystems. Vulnerability of a given site is measured by exceeding the maximum concentrations (according to the EPA standards) at a given probability level.
Supplemental Keywords:wetland, water, ecosystem, stress. , Ecosystem Protection/Environmental Exposure & Risk, Water, Geographic Area, Scientific Discipline, Waste, RFA, Ecosystem/Assessment/Indicators, Water & Watershed, Engineering, Chemistry, & Physics, Civil/Environmental Engineering, Chemistry, Environmental Engineering, Fate & Transport, Hydrology, Watersheds, Ecological Effects - Environmental Exposure & Risk, Ecosystem Protection, West Coast, Regional/Scaling, Monitoring/Modeling, International, remediation, risk assessment, water quality, water table, Sacremento River, fate and transport, regional scale, stream flow, model ecosystem effects, river systems, degradation, eco-system quality, groundwater, wetland, wetlands, surface water, contaminated aquifers, heterogeneity, nitrates, Salinas Valley, Tahoe Basin, agriculture, contaminant transport, subsurface, nutrient transport model, contaminated waters, Pope Marsh, pesticides, groundwater contamination, hydrological, groundwater flow, lake ecosysyems, ecosystem, modeling, difffusion, industrial waters, Borden Aquifer (Ontario, Canada), ecological impacts, pollutant transport, transport, transport contaminants, solute transport, river ecosystems, model structure
Progress and Final Reports:
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