Sediment cores are useful tools in reconstructing the history of aquatic ecosystems. Many parameters, stresses and responses at the time of sediment deposition cause specific signals in a core. The USGS raised some very deep cores (115m long, representing 450,000 years) during the 1970s and 80s for work on the long time scale, and the UC Davis Mercury Project raised some shallow cores (~1m, representing 50-75 years) during 1992 to investigate changes in sediment Hg since the last mining episode. We are now interested in cores of 2-3 meters length, which will reflect the last 250-350 years of changes in the lake in order to assess the kinds of natural and anthropogenic stresses applied since the advent of European colonization. In collaboration with several other subprojects, we are also investigating the documentary history available to reconstruct stress events and responses. A combination of cores and standard historical analysis, together with process-oriented investigations, should result in an excellent reconstruction of past stresses and their effects.
For the past ten months we have been designing a sampling protocol and methodology and gathering historical information for the Clear Lake ecosystem. Because Clear Lake is relatively shallow, we have been able to design a simple hand-driven coring device that allows us to sample the whole historical sequence well back into the pre-European period. These cores will be dated (210Pb) and analyzed for a large number of parameters (x-ray, nutrients, Hg, diatoms, pollen, algal pigments, etc.). This will allow us to reconstruct the effects of major events in the basin (i.e. dam construction, logging, road building, stream channel disturbance, mining activities, residential development, etc.) on the physical and biological responses that can be detected in cores, such as sediment rate and planktonic community composition. The methodology is in place, some preliminary cores have been raised and used to work out the problems of sampling and analysis, and the historical research has been started. During the next year, we will raise six cores from Clear Lake and have them analyzed for the different parameters. There will be two cores raised from each of the three basins of the lake. By doing this, we can test how deposition has changed, both within the basins and between the basins.Previous research has shown that Lake Tahoe, which is in the earliest stage of eutrophication, has made a fundamental switch from a classically N-limited system to one that is increasingly sensitive to P. Studies by the Tahoe Research Group (TRG), directed by Dr. Goldman, and including Drs. Reuter and Jassby, indicate that the shift in lake nutrient limitation from N to P can be attributed to atmospheric N deposition from both in-basin and out-of-basin N sources. Most of the P entering the lake ultimately comes from the watershed, as has been shown by extensive monitoring data collected in conjunction with the TRG's Lake Tahoe Interagency Monitoring Program. P loading from the Tahoe watershed is the current focus of this project.
Graduate student Lorin Hatch is currently nearing completion of his Ph.D. thesis research on the generation and transport of P in the Lake Tahoe ecosystem, with particular emphasis on biologically available P to lake phytoplankton. Research in the last year has examined the temporal and spatial variability of P in ten Tahoe streams, with the most intensive work on two streams that are located in a fragile but urban-stressed area of the basin. Mr. Hatch has been conducting 24-hour studies on these two creeks, once a month over the course of the snowmelt season. A publication is currently being prepared, and results were presented at the North American Lake Management Society annual meeting in Toronto (November 6-10, 1995). Mr. Hatch has also been assembling a 15-year data set on discharge, P, and suspended sediment data collected for the Lake Tahoe Interagency Monitoring Program. Preliminary results were presented at the American Society of Limnology and Oceanography annual meeting in Reno, NV (June 1995) and more intensive analysis is currently under way.
Ongoing urbanization in the Tahoe basin is disturbing the fragile soils, increasing the erosion and delivery of P-rich sediments to the lake. Soils of nine major watersheds in the Tahoe basin have been analyzed for several P fractions in order to determine the actual P bioavailability associated with potential yield from various land-use practices. Mr. Hatch will address the subject of urban stress on the Tahoe ecosystem this coming year with the results of his intensive stream and lake analysis. Stream water samples from both above and below areas of human development will serve as nutrient spikes to lake water bioassay experiments, determining more precisely how land disturbance has enhanced the ongoing eutrophication of Lake Tahoe. This information will be combined with land classification parameters such as bioavailable P will enter the lake from various types of land disturbance.
Our goal is to incorporate a P yield potential into an improved land classification scheme. This should make it possible to incorporate P input into a geographical information system to yield important management directions so that remedial work on the watershed can most effectively address the problem of nutrient stress on the fragile Tahoe ecosystem as well as other lakes.
For the past ten months we have been designing a sampling protocol and methodology and gathering historical information for the Clear Lake ecosystem. Because Clear Lake is relatively shallow, we have been able to design a simple hand-driven coring device that allows us to sample the whole historical sequence well back into the pre-European period. These cores will be dated (210Pb) and analyzed for a large number of parameters (x-ray, nutrients, Hg, diatoms, pollen, algal pigments, etc.). This will allow us to reconstruct the effects of major events in the basin (i.e. dam construction, logging, road building, stream channel disturbance, mining activities, residential development, etc.) on the physical and biological responses that can be detected in cores, such as sediment rate and planktonic community composition. The methodology is in place, some preliminary cores have been raised and used to work out the problems of sampling and analysis, and the historical research has been started. During the next year, we will raise six cores from Clear Lake and have them analyzed for the different parameters. There will be two cores raised from each of the three basins of the lake. By doing this, we can test how deposition has changed, both within the basins and between the basins.The goal is to develop and verify a mathematical model for anaerobic biotransformations in the presence of competing electron acceptors, and to measure process kinetic constants. Electron acceptor interactions between chlorophenols and their dechlorinated metabolites and interactions between chlorophenols and sulfate are examined.
The HSRC program provided a national program of basic and applied research, technology transfer, and training. Five multi-university centers, each located in a pair of federal regions, focused on different aspects of hazardous substance management. They brought together researchers from a variety of disciplines to collaborate on integrated research projects.
The HSRCs were funded by EPA, DOE, DOD, academia, and other state and federal government agencies. The centers shaped their research agendas with the assistance of advisory committees made up of representatives from industry, regulatory organizations, academic institutions, and government.
The Western Region center covered EPA Regions 9 and 10, and is led by Stanford University, with Oregon State University participating. This HSRC focused on groundwater cleanup and site remediation with a strong emphasis on biological approaches. Projects addressed chlorinated solvents; halogenated aromatics (pentachlorophenol and PCBs); nonhalogenated aromatics including petroleum derivatives; ordinance wastes (TNT); heavy metals; and transport and fate.