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The San Joaquin area is part of two studies assessing surface water trends in major river basins. These studies are:

Nutrient trends in California streams, 1975-2004

This study includes an assessment in nutrient trends in three California NAWQA study units: the Sacramento River Basin (SACR), the San Joaquin-Tulare Basins (SANJ), and the Santa Ana River Basin (SANA). The objectives of the study were:

Define trends in nutrient concentrations and loads in three major California river basins and explain (to the extent possible) the reasons for the trends. This explanation will require evaluating many forms of ancillary data on nutrient sources and their changes over time. All MRB reports will evaluate trends over the period of 1993-2004. In addition, we will evaluate trends in the SANJ for 1985-2004 and at the three integrator sites (Sacramento River at Freeport, San Joaquin River near Vernalis, and Santa Ana River below Prado) for 1975-2004. Discuss a SPARROW model application for the Central Valley (SACR and SANJ) to the extent possible.

A USGS report on this study will be published later in 2009. The tentative report title is “Trends in nutrient concentrations, loads, and yields in streams in the Sacramento, San Joaquin, and Santa Ana Basins, California, 1975-2004”.

Trends in concentration and loads of selected pesticides relative to application, and potential toxicity to aquatic life in western streams, 1991-2005

This study includes as assessment of pesticide trends in seven western NAWQA study units within MRBs 7 and 8: the Sacramento River Basin (SACR), the San Joaquin-Tulare Basins (SANJ), the Santa Ana River Basin (SANA), the Willamette River Basin (WILL), the Puget Sound Drainages (PUGT), the Central Columbia and Yakima Basins (CCYK), and the Upper Snake River Basin (USNK). The objectives of the study are:

Define trends in concentrations and loads of dissolved pesticides and relate these trends to available application data for 1991 to 2005. The California study units have the unique opportunity to do this sort of trend analysis because of the State database on application. The application data are reported for this time period by pesticide use per day per square mile. Although the study units in Oregon and Washington do not have this level of detail, county level data are available which will be applicable to larger watersheds.

Both agricultural and urban land uses will be investigated. The urban focus will be on PUGT, SANA, and selected SACR and WILL sites. Agriculture will be the primary land use studied in SANJ, CCYK, and selected SACR and WILL sites. Similarities and differences between the two land uses will be made where possible.

Modeled pesticide concentrations will be interpreted for potential toxicity to aquatic organisms using three, possibly four, approaches. First, the modeled daily average pesticide concentrations will be compared to existing acute and chronic criteria, as available, with appropriate exposure windows (i.e., 14, 21, or 30-day moving average). Secondly, complete mixtures will be evaluated for toxicity to three general organism classes (invertebrates, cladocerans, and fish) using the Pesticide Toxicity Index (PTI). Third, classes of pesticides will be grouped by common modes of action (organophosphates, carbamates, triazines, phenoxy herbicides, and organochlorines as available) and weighted by efficacy and summed to evaluate potential additivity to a common receptor. This approach will be specific to a particular group of organisms of particular regional concern (e.g., ESA-listed salmonids). Fourth, for those pesticides that have sufficient and comparable toxicity endpoints, the distribution of species sensitivity (SSD) will be modeled for a community of stream organisms; algae, invertebrates, or fish. This distribution of species sensitivity will allow a prediction of the number or percent of species likely to be effected at a given pesticide concentration. These approaches will build on the load and trend estimations produced from the modeling efforts.

More information on these studies and the overall NAWQA major river basin studies can be accessed at the following URL:


Some trend results for the San Joaquin study area are listed in the presentations and publications.

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Page Last Modified: Tuesday, 14-Jun-2011 14:18:28 EDT