By Charles R. Kratzer, Peter D. Dileanis, Celia Zamora, Steven R. Silva, Carol Kendall, Brian A. Bergamaschi, and Randy A. Dahlgren
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 03-4127
Sacramento, California 2004
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Oxidizable materials from the San Joaquin River upstream of Vernalis can contribute to low dissolved oxygen episodes in the Stockton Deep Water Ship Channel that can inhibit salmon migration in the fall. The U.S. Geological Survey collected and analyzed samples at four San Joaquin River sites in July through October 2000 and June through November 2001, and at eight tributary sites in 2001. The data from these sites were supplemented with data from samples collected and analyzed by the University of California at Davis at three San Joaquin River sites and eight tributary sites as part of a separate study. Streamflows in the San Joaquin River were slightly above the long-term average in 2000 and slightly below average in 2001. Nitrate loads at Vernalis in 2000 were above the long-term average, whereas loads in 2001 were close to average. Total nitrogen loads in 2000 were slightly above average, whereas loads in 2001 were slightly below average. Total phosphorus loads in 2000 and 2001 were well below average. These nutrient loads correspond with the flow-adjusted concentration trends--nitrate concentrations significantly increased since 1972 (p < 0.01), whereas total nitrogen and total phosphorus concentrations did not (p > 0.05). Loading rates of nutrients and dissolved organic carbon increased in the San Joaquin River in the fall with the release of wetland drainage into Mud Slough and with increased reservoir releases on the Merced River. During August 2000 and September 2001, the chlorophyll-a loading rates and concentrations in the San Joaquin River declined and remained low during the rest of the sampling period. The most significant tributary sources of nutrients were the Tuolumne River, Harding Drain, and Mud Slough. The most significant tributary sources of dissolved organic carbon were Salt Slough, Mud Slough, and the Tuolumne and Stanislaus Rivers. Compared with nutrients and dissolved organic carbon, the tributaries were minor sources of chlorophyll-a, suggesting that most of the chlorophyll-a was produced in the San Joaquin River rather than its tributaries. On the basis of the carbon-to-nitrogen ratios and the δ13C of particulate organic matter in the San Joaquin River and tributaries, the particulate organic matter in the river was mostly phytoplankton. On the basis of the δ15N values of the particulate organic matter, and of total dissolved nitrogen and nitrate, the nitrate in the San Joaquin River probably was a significant nutrient source for the phytoplankton. The range of δ15N and δ18O values of nitrate in the San Joaquin River and tributaries suggest that animal waste or sewage was a significant source of nitrate in the river at the time the samples were collected.
Abstract
Introduction
Study Area
Methods of Data Collection and Analysis
Sample Collection and Processing
U.S. Geological Survey Methods
University of California at Davis Methods
Field Measurements and Streamflow
Analytical Methods
U.S. Geological Survey Methods
Organic Carbon, Ultraviolet Absorbance, and Volatile Suspended Solids
Chlorophyll-a and Pheophytin-a
Suspended Sediment
Isotopes
University of California at Davis Methods
Nutrients
Organic Carbon and Particulate Organic Matter
Chlorophyll-a and Pheophytin-a
Total Suspended Solids
U.S. Geological Survey Quality Control Samples
Hydrologic Conditions During the Study Period
Concentrations of Nutrients, Organic Carbon, and Chlorophyll-a
Nitrogen
Phosphorus
Organic Carbon
Chlorophyll-a and Pheophytin-a
Historical Nutrient Loads in the San Joaquin Basin
Monthly Loads in the San Joaquin River near Vernalis, 1972-2001
Upstream-to-Downstream Loads in the San Joaquin River, 1986-88
Loading Rates of Nutrients, Organic Carbon, and Chlorophyll-a
Nitrogen
Phosphorus
Organic Carbon
Chlorophyll-a and Pheophytin-a
Isotopes
Sources of Particulate Organic Matter
Nitrate as a Nutrient Source to Phytoplankton
Sources of Nitrate
Summary and Conclusions
References Cited
Appendixes
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