Temporal and Spatial Assessment of Water Quality, Physical Habitat, and Benthic Communities in an Impaired Agricultural Stream in California's San Joaquin Valley

The goal of this study was to characterize and discuss the relationships among water quality, physical habitat, and benthic community data collected annually over a three–year period (2000–2002) in an impaired agricultural stream (Orestimba Creek) in California's San Joaquin River watershed. Conductivity, pH, and turbidity were the most important water quality conditions influencing the various benthic metrics. Significantly higher flow conditions and lower dissolved oxygen values were reported in Orestimba Creek in 2001; increased turbidity conditions were reported in 2002. Channel alteration, riparian buffer, sediment deposition, and channel flow were the most important physical habitat metrics influencing the various benthic metrics. Higher total physical habitat scores were reported in 2001 when compared with 2002. The most dominant benthic taxa collected during all three years of sampling were oligochaetes and chironomids. Oligochaetes are found in stressful environments while chironomids can be either sensitive or tolerant to environmental stressors depending on the species. Populations of both daphnids and the exotic clam Corbicula were reported to increase over time. Both of these taxa are generally tolerant to most types of environmental degradation. The exception is that daphnids are highly sensitive to organophosphate insecticides. The % filterers increased over time, which suggests an increase in environmental disturbance. The % collectors decreased from 2000 to 2002, which suggests an improvement in environmental conditions. The presence of ∼100 taxa in Orestimba Creek during each of the three years of sampling implies that benthic communities in this stream are fairly diverse, considering their ephemeral environment, but without a clear definition of benthic community expectations based on established reference conditions it is unknown if this water body is actually impaired.

Key Words :

• San Joaquin River watershed
• Agricultural stream
• Benthic communities
• Physical habitat.

ACKNOWLEDGMENTS

We would like to thank Dow AgroSciences and the University of Maryland for supporting this study. Special consideration is extended to our project officers, Dr. Nick Poletika and Dr. Mike Shaw, for their valuable contributions. Dr. Elgin Perry is acknowledged for conducting the statistical analysis. Jeff DeBerardinis, Brian Mayer, and Michelle Osborn are acknowledged for assisting with field work. Jim Harrington and Angie Louis Montalvo of the California Department of Fish and Game are acknowledged for directing the identification of benthic species. We would also like to thank the following landowners for allowing access to their property near Orestimba Creek: Mr. Glenn Crow, Mr. Norman Crow, Mr. Marvin Kaminska, Mr. Anthony George, and Mr. Clyde Peters.

Notes

⁺Friedman test if three years, Wilcoxon signed rank test if two years.

^*<0.05 by Wilcoxon signed rank test.