HR: 0800h
AN: H51B-0445    [Abstracts]
TI: Seasonal and Interannual Variations of Stream Chemistry in an Urban Fringe Watershed in Southern California
AU: Hogue, T S
EM: thogue@seas.ucla.edu
AF: UCLA, 5732 Boelter Hall Department of Civil and Environmental Engineering, Los Angeles, CA 90095-1593, United States
AU: * Barco, J
EM: ojbarco@ucla.edu
AF: UCLA, 5732 Boelter Hall Department of Civil and Environmental Engineering, Los Angeles, CA 90095-1593, United States
AU: Rademacher, L
EM: lrademacher@pacific.edu
AF: University of the Pacific, Department of Geosciences 3601 Pacific Avenue, Stockton, CA 95211, United States
AB: Understanding the hydrological, geochemical and biological watershed processes involved in ecosystem evolution involves numerous scientific challenges. The transition from undisturbed to urbanized landscapes has impacted ecosystems worldwide. Of critical concern is ecosystem degradation in undisturbed watersheds due to regional atmospheric deposition. This study focuses on the undeveloped, upper reaches of the Arroyo Seco watershed, located on the eastern edge of the Los Angeles basin, where estimates of dry deposition are considered some of the highest in North America. Weekly water quality grab samples were collected from April 2004 to December 2006 and analyzed for standard geochemical constituents. Atmospheric wet deposition for different constituents was obtained from the National Atmospheric Deposition Program (NADP) site located in eastern Los Angeles County. Hydrologic, geochemical and atmospheric data were assessed at various time scales to evaluate current hydro-geochemical dynamics and ecosystem response to the impacts of large-scale regional urbanization. For almost all the constituents, streamwater concentrations are higher in the fall and lower in the spring, while atmospheric wet deposition values are higher in the summer and lower in the winter. The streamwater chemistry also exhibits interannual variation which can be primarily explained by the interactions of the hydrological and biogeochemical cycles. Seasonal stream concentration-discharge relationships were developed using a hyperbolic dilution model. In general, the developed model results in a better fit for the cations rather than anions. Model results were used to predict seasonal and annual mass loadings to downstream urban streams. Both observations and model predictions indicate the watershed is a sink for atmospheric nitrate and a source for various cations.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1804 Catchment
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2007 Fall Meeting