Migrating fall-run Chinook salmon can hit a stretch of the San Joaquin River in Central California with oxygen levels so low, the fish are forced to either wait around until conditions improve or to go elsewhere to spawn, thereby negatively affecting their spawning success. Algae consume much of the oxygen and according to a recently published U.S. Geological Survey (USGS) report, animal wastes or sewage were a major source of nutrients for the algae growth.
“Whereas tributaries were important sources of nutrients and organic carbon in the San Joaquin River, they were a relatively minor source of algae” said the report’s lead author, Charles Kratzer, a USGS hydrologist. "Nitrate was an important nutrient source for the algae growth in the San Joaquin River and the isotopic signature of the nitrate in the river suggested that animal waste or sewage was a significant source of the nitrate at the time of sampling."
Samples were collected in the summer and fall of 2000 and 2001 at 7 sites on the San Joaquin River in the Sacramento-San Joaquin Delta and 14 sites on tributaries. Analyses of the samples looked at nutrients, organic carbon, chlorophyll-a, and isotopes of carbon, nitrogen, and oxygen in the water and in the particulate organic matter.
The California Department of Water Resources and the CALFED Bay-Delta Program funded the USGS study to provide additional information to the Central Valley Regional Water Quality Control Board for their development of a Total Maximum Daily Load regulation for dissolved oxygen levels in the Stockton Deep Water Ship Channel. The sampling in this study was coordinated with a study done by the University of California at Davis (UCD). The U.S. Fish and Wildlife Service funded the UCD study to evaluate the food resources to the Sacramento-San Joaquin Delta from the Sacramento and San Joaquin Basins. The UCD data is included and interpreted in the USGS report.
The USGS report entitled, “Sources and Transport of Nutrients, Organic Carbon, and Chlorophyll-a in the San Joaquin River Upstream of Vernalis, California, during Summer and Fall, 2000 and 2001,” by Charles R. Kratzer, Peter D. Dileanis, Celia Zamora, Steven R. Silva, Carol Kendall, Brian A. Bergamaschi, and Randy A. Dahlgren, can be found on the web at http://water.usgs.gov/pubs/wri/wri034127/
The USGS serves the nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.
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