Aquatic Biology of the San Joaquin-Tulare Basins, California: Analysis of Available Data Through 1992

Larry R. Brown

U.S. Geological Survey Water-Supply Paper 2471

Abstract:
Available data on the biology of fish, aquatic macroinvertebrates, aquatic algae, and concentra tions of trace elements and organic pesticides in aquatic biota were analyzed to provide a conceptual overview of these issues in the San Joaquin­Tulare Basins study unit of the National Water-Quality Assessment Program. This conceptual overview will guide the study designs for assess ments of the structure of biological communities and occurrence of contaminants in tissues. These studies are an integral part of the multidisciplinary approach of the National Water-Quality Assessment Program.

The native fish fauna of the San Joaquin­Tulare Basins study unit included 21 species of fish. Of these, 14 species and 1 subspecies were endemic to California. Abundance of native species declined beginning in the mid-1800's as a result of habitat loss, introduction of exotic species, and changes in land and water use. The construction of reservoirs and diversion dams was especially detrimental because the altered physical conditions downstream from dams favored introduced species. Streams on the San Joaquin Valley floor now are dominated by introduced species, and native species are rare, extirpated, or extinct.

Historical information on native benthic macroinvertebrates and benthic algae in the study unit is limited, but it is likely these taxa have declined in distribution and abundance. In addition to physical changes associated with water development, exotic fish and invertebrates introduced into high-altitude lakes and streams that were naturally without fish likely have affected the native fauna through predation and competition.

The biology of fishes is significantly affected by altitude, stream gradient, stream order (size), and correlated physical and chemical aspects of the aquatic environment. Responses of individual species to these physical factors result in patterns of species cooccurrence that can be described as different assemblages. The rainbow trout assemblage is associated with cold, clear, steep headwater streams and altitudes greater than 1,500 feet above sea level. The squawfish-sucker-hardhead assemblage is associated with moderate stream gradient, warmer temperatures, and altitudes ranging from about 100 to 1,500 feet above sea level. Introduced species may be present in both of these assemblages and are replacing native species in some areas. The deep-bodied fish assemblage that originally existed on the valley floor has been almost completely replaced by introduced species. The California roach assemblage is associated with small intermittent streams and has been replaced by green sunfish and mosquitofish in some areas.

Benthic macroinvertebrates and benthic algae have not been studied as often as fishes. Benthic macroinvertebrate studies indicate that intermittent streams support a different group of species than perennial streams. Data on benthic algae are so limited that generalizations are not possible, although data on phytoplankton indicate increasing species richness with decreasing altitude.

A considerable amount of data is available on trace elements in biota in the study unit. At least four tissue samples from fish or bivalve mollusk (Corbicula fluminea) have been analyzed for each of 21 trace elements; trace elements of particular interest, such as selenium and mercury, have been sampled more intensively, with hundreds of samples collected. Nineteen elements were detected, and concentrations of 10 trace elements exceeded California criteria used to screen results. Of these, arsenic, boron, molybdenum, and selenium are of the most concern in the study unit.

Organic pesticides in biota have been studied less than trace elements, but some data are available. Thirty-five chemicals have been detected in the tissues or lipids of fish and Corbicula. Most of these pesticides were present in low concentrations, but several exceeded California criteria. The exceptions included total chlordane, total DDT, hexachlorobenzene, toxaphene, and chemical group A.

Limited data were available for the study unit on the effects of dissolved solids or atmospheric acid deposition on biota, toxicity of surface waters to biota, biological indicators, or distribution and abundance of microorganisms in surface water. Laboratory experiments showed that concentrations of dissolved solids in agricultural drainwater caused mortality and limited growth of chinook salmon and striped bass. Atmospheric acid deposition is not a threat to biota at this time, but experiments indicate that some benthic macroinvertebrates and benthic algae are sensitive to changes in acidity and may serve as bioindicators. U.S. Geological Survey data indicate a general pattern of increased densities of fecal-indicator bacteria at lower altitudes. However, Giardia, a protozoan, is widespread in the study unit. Bioassays have been useful for determining toxicity levels of surface water in the study unit but have not identified specific contaminants or groups of contaminants. A test of the Index of Biotic Integrity indicates that its usefulness may be limited in the San Joaquin­Tulare Basins study unit.