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Region 9 CA Central Valley Project Information

Text reproduced from the publication, USEPA 1993. Regional Environmental Monitoring and Assessment Program. EPA/625/R-93/012. September 1993. U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC.

Figures and tables not reproduced here. The complete publication may be ordered from the U.S. Environmental Protection Agency, Center for Environmental Research Information, Cincinnati, OH 45268. The publication request desk may be reached by phone at 513-569-7562.


California's Central Valley, which comprises more than 48,000 miles of surface water and 16 percent of the land area of California, is one of the nation's most productive agricultural areas. EPA and the state of California are concerned, however, that agricultural practices might be jeopardizing the health of wildlife and the quality of aquatic ecosystems throughout the Central Valley. The Central Valley contains ecologically critical and highly impaired habitat for both aquatic and terrestrial resources. As a result of pesticide runoff, resident fish populations such as striped bass, chinook salmon, and delta smelt have experienced sharp declines in the last decade, and some are now listed as threatened or endangered species. Many wildlife deaths and deformities have been linked to selenium that is dissolved from soil by irrigation and enters surface water. In addition, many bird populations are in a steep decline due to the lack of high-quality wintering habitat.

Previous studies focusing on the Sierra foothill streams and the San Francisco Bay Delta have indicated that human-related activities, such as contamination by agricultural wastes, have contributed to the decline in environmental conditions for aquatic life. However, the aquatic biological communities in the waters of the Central Valley have not been comprehensively evaluated. The Region IX R-EMAP project seeks to assess the current condition of aquatic resources in the Central Valley, focusing on constructed agricultural drains (ditches) and natural waterbodies affected by agricultural management practices. The geographic target area of the project is the whole watershed of the Sacramento-San Joaquin Valley, approximately 24,000 square miles.

The objectives of the Region IX R-EMAP study are to:

The Region IX R-EMAP project will be jointly managed by staff from the EPA Region IX Environmental Services Branch and Water Management Division. California's Department of Fish and Game will be responsible for most of the data collection and taxonomic work.


The Region IX R-EMAP project will assess the biotic integrity of agriculture-dominated waterbodies in the Central Valley. Some drains are thought to provide extremely important habitat, supporting biota where the original habitat has been highly modified or destroyed. Even before the concentrations of agricultural chemicals reach toxic levels, sensitive species may disappear and native biotic diversity may decrease. To assess the health of aquatic communities, the Region IX R-EMAP project will categorize these waterbodies based on:

This will allow the investigators to assess the overall health of the resources and the biological condition of each waterbody. Depending on the results, the sampled waterbodies may be re-categorized according to additional critical features.

To accomplish the project objectives, the investigators will undertake the following activities:

Table 9-1 shows the schedule and milestones for the Region IX R-EMAP project.



The Region IX R-EMAP project will focus exclusively on California's Central Valley. The monitoring network will be established by overlaying the national EMAP 12,600 40-km2 hexagon frame over the California Central Valley. Figure 9-1 illustrates this for an example watershed, the Middle San Joaquin. (Agricultural drains are shown as dotted lines.)

The investigators will then randomly select sampling sites within the hexagons for field monitoring. These sites will be selected to represent all classes of waterbodies highly affected by agricultural land use. During the first year, the investigators will select and sample approximately 80 sites in the Sacramento-San Joaquin Valley. An additional 10 to 20 sites will be selected and sampled to reflect representative agricultural waters throughout the Valley. At each site, measurements will include fish and macroinvertebrate collections, physical habitat assessments, and basic water chemistry analyses. (Macroinvertebrates will be collected using a standard D-frame dip net; fish will be collected using electrofishing equipment.)

In the project's second year, the field crew will revisit the same sites, one-half during the same index (sampling) period and one-half during a different index period. The researchers will evaluate how the measurements vary between seasons and how the target communities vary between the two sampling years.


The Region IX R-EMAP project will use fish and macroinvertebrate assemblages as indicators of response to environmental stressors. The study will assess these organisms (number, species, length and weight, and presence of external abnormalities) to determine if they have been affected by chemical, physical, or biological changes in their habitats. The response indicators used in this study will not directly identify the causes of problems originating from certain land-use practices. Rather, they will allow investigators to determine associations between measured indicators and potential stressors. Subsequent studies could investigate further to determine the probable causes of impacts such as contamination from agricultural pesticides, habitat alterations, and nutrient loadings.

Two nationally recognized indices of biotic integrity, the Rapid Bioassessment Protocol and the Index of Biotic Integrity, were developed using very different streams and communities than those in the Central Valley. This project will determine what modifications to these indices are needed to accurately assess the current condition of aquatic biota in the Central Valley.

The study will use the habitat parameters listed in Table 9-2 (for nontidal coastal plain streams) and Table 9-3 (for reaches where glides and pools are prevalent). Water chemistry indicators will include temperature, dissolved oxygen, pH, conductivity, turbidity, and flow.


The Region IX R-EMAP project will test the following hypotheses:

The results of this study will help states with irrigated agriculture to assess their agriculture-dominated waterbodies and develop meaningful, realistic water quality standards for agricultural drains. The study will also help meet the need for scientifically supported environmental quality standards to measure the health of these ecosystems.



Gary Wolinsky
Water Management Division
Region IX
U.S. Environmental Protection Agency
Mail Code W3-175 Hawthorne Street
San Francisco, CA 94105 (415) 744-2015

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