Eutrophication Modeling to Aid in the Development of a TMDL for the Salton Sea, California
Project Number: 9KM32
Project Chief: Dale M. Robertson
Project Topics:Water quality and Southern California
Cooperators: University of California, Davis
Period of Project: October 2003– 2008
An upwelling on the north end of the Salton Sea, induced by northerly winds, can be observed on May 28, 2001, from this MODIS/Terra thermal infrared image. On the following day, a fish kill totaling an estimated 1,269,200 fish was reported as having occurred at the north end of the Sea, between Desert Shores and Mecca.
The Salton Sea is a eutrophic to hypereutrophic water body in southern California characterized by high nutrient concentrations, high algal biomass as demonstrated by high chlorophyll a concentrations, high fish productivity, low clarity, frequent very low dissolved oxygen concentrations, massive fish kills, and noxious odors. Its eutrophic condition is primarily controlled or limited by phosphorus concentrations in the Sea. Most of the phosphorus input to the Salton Sea on an annual basis is from tributary loading; however, it is uncertain how important the release of phosphorus from the sediments of the Sea (associated with resuspension or redox conditions at the sediment surface) is to driving short-term algal blooms and anoxic conditions. To reduce the phosphorus loading to the Sea, a Total Maximum Daily Load (TMDL) is being prepared by the California Regional Water Quality Control Board, that, if implemented, is intended to improve the water quality and eliminate/reduce the problems with eutrophication. To determine a TMDL for phosphorus that will reduce the productivity of the Salton Sea to acceptable limits and reduce the extent of fish kill and noxious odors, a better understanding is needed for the link between nutrient loading from the watershed and sediments and the water quality of the Sea.
The work proposed by the USGS is part of a collaborative effort with the University of California, Davis (Dr. S. Geoff Schladow, Dept. of Civil and Environmental Engineering), and the National Aeronautics and Space Administration (Dr. Simon Hook). The objectives of the USGS part of the study are: (1) refine all of the inputs (hydrologic and nutrient loading) to the Salton Sea, (2) determine what are the most important factors influencing short-term (daily) and long-term (annual and longer) productivity of the Salton Sea, (3) determine how modifications to the nutrient loading to the Sea should affect its short- and long-term productivity, and (4) in collaboration with the University of California, help the California Regional Water Quality Control Board establish a TMDL for the Salton Sea.
Historical data describing water quality in the Salton Sea and its tributaries will be assembled from the various agencies that collected the original data. Tributary loading will be estimated using the USGS load-estimating program Estimator, based on flow-to-load relations based on water-quality data and corresponding daily flow estimates from 1969 to 1999. To determine the sensitivity of the Salton Sea to decreases and increases in phosphorus loading, the BATHTUB model and other empirical models will be calibrated using lake and tributary data collected in 1999 and used to simulate conditions in the Sea with incremental increases and decreases in phosphorus loading. A dynamical model will also be developed by the University of California, Davis to describe how changes in the water quality of the Salton Sea should respond to decreases and increases in phosphorus loading. The results of the two different approaches will be compared.
Robertson, D.M., and Schladow, S.G., 2008, Response in the water quality in the Salton Sea to changes in phosphorus loading: An empirical modeling approach: Hydrobiologia, v. 604, p. 5–19. doi:10.1007/s10750-008-9321-4
Chung, E., Schladow, S.G., Perez-Losada, J., and Robertson, D.M., 2008. A linked hydrodynamic and water quality model for the Salton Sea: Hydrobiologia, v. 604, p. 57–75. doi:10.1007/s10750-008-9311-6
Robertson, D.M., Schladow, S.G., and Holdren, G.C., 2008, Long-term changes in the phosphorus loading to and trophic state of the Salton Sea: Hydrobiologia, v. 604, p. 21–36. doi:10.1007/s10750-008-9312-5