By Larry R.
Brown and Jason T. May
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5098
Sacramento, California 2004
ONLLINE ONLY
Prepared in cooperation with the Central Valley Regional Water Quality Control Board
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The effects of agriculture, particularly from the
use of pesticides, on aquatic ecosystems in the San Joaquin River Basin concern
many aquatic resource managers, water quality managers, and water users. A total
of five sites were sampled once in June 2001 and once in September 2001 to document
the periphyton (attached algae) community, the benthic macroinvertebrate (insects
and non-insects) community, and stream habitat conditions. The purposes of the
study were to document existing conditions and, to the extent possible, relate
the periphyton and macroinvertebrate community condition to environmental conditions.
A total of 161 taxa of algae were collected during
the study. Samples from the richest targeted habitat, woody debris, included
109 taxa. In both the June and September samples, greater than 95 percent of
the taxa collected were diatoms. Cluster analysis and detrended correspondence
analysis of sample data showed that Orestimba Creek had a very different periphyton
community than the Merced and Tuolumne Rivers. Salt Slough and the San Joaquin
River had community compositions that were intermediate between the two extremes.
A total of 126 taxa of macroinvertebrates were collected during the study. Samples
from woody debris included 59 taxa. The samples included a variety of both insect
and non-insect taxa. Cluster analysis and detrended correspondence analysis
of sample data showed that Orestimba Creek was very different from the Merced
River and Tuolumne River, similar to the results for periphyton. Orestimba Creek
was dominated by non-insects, while the Merced and Tuolumne Rivers were dominated
by insects. Salt Slough was more similar to Orestimba Creek because of the abundance
of non-insects. The San Joaquin River was more similar to the Merced and Tuolumne
Rivers.
There was no evidence of major differences between
June and September samples for either the periphyton or macroinvertebrate communities.
Specific conductance (a surrogate for salinity) and several habitat measures
were associated with differences in the periphyton and macroinvertebrate communities
at the five sites. Additional sampling at more sites over a longer period of
time will likely be necessary before the effects of water quality and habitat
conditions on aquatic communities are fully understood in the San Joaquin River
Basin.
Abstract
Introduction
Purpose and Scope
Study Area
Methods
Sampling Design
Periphyton
Benthic Macroinvertebrates
Data Analysis
Results and Discussion
Environmental Variables
Periphyton
Macroinvertebrates
Summary and Conclusion
References
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