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Larry R. Brown, Charles R. Kratzer and Neil M. Dubrovsky
From cumulative impacts towards sustainable solutions -- Critical
methodologies for the study of ecosystem health: Davis, California, Center
for Ecological Health Research, Agenda and Abstracts, 1996, p. 4.
The purpose of the National Water Quality Assessment Program of the
U.S. Geological Survey is to describe current water quality conditions,
define long-term trends in water quality, and elucidate the natural and
human-induced processes that affect water quality in the United States.
One objective of the NAWQA Program's surface-water investigations is to
combine multiple lines of evidence to explain the interrelations between
aquatic biological communities and their environment. Studies in the San
Joaquin-Tulare basins study unit of the NAWQA Program have focused on the
lower San Joaquin River and its tributaries, particularly the Merced, Tuolumne,
and Stanislaus Rivers. The surface-water design included collection of
physical, chemical, and biological data at varying temporal and spatial
scales, ranging the hourly measurements of dissolved pesticide concentrations
at one site during a rainstorm, to synoptic studies where single samples
were collected at each site over a broad geographic range. A direct link
between aquatic biota and their environment was shown by the strong correlation
between concentrations of contaminants in bed sediment and organisms. Similarly,
the species composition of the fish assemblage at each location was correlated
with overall water quality conditions. However, species composition of
fish assemblages also correlated with overall habitat quality as affected
by land and water use. Fish assemblages are useful as indicators of overall
habitat and water quality, but the elucidation of causal mechanisms is
currently problematic because of strong covariance between measures of
habitat and water quality.
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U.S. Department of the Interior | U.S.
Geological Survey