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Results
During the period 1992-1999, 1457 samples of 76 species
of aquatic organisms were collected by the NAWQA Program
for determination of trace-element concentrations in selected tissues; the
trace-element concentrations are presented in table 1A. The meanings of the
column names (metadata) in this table are presented in table 1B.
Table 1. (A) Trace-element
concentrations and
percent moisture in aquatic tissue samples, 1992–1999,
(B) Metadata for column headings
A summary of the number of samples collected by species
and tissue type is shown in table 2 (included in table1A). The
most commonly collected sample types were: common carp livers (248 samples), asiatic
clam edible portion (183 samples), white sucker livers (160 samples), common
carp whole organisms (76 samples), and net-spinning caddisfly larvae whole
organisms (67 samples).
Table 2. Number of samples by species and tissue type.
A summary of the number of samples collected by species
and study unit is shown in table 3. This table provides an indication of the
geographic distribution of samples. Only species with 10 or more total samples
are shown in this table; an additional 300 samples were collected for
miscellaneous species and are not shown in table 2. Common carp were collected
in the most study units (30 study units), although the number of common carp
samples per study unit ranges widely, from 1 to 18 (not including the 189
samples collected as part of the special REDN mercury study). White sucker were
the second most commonly collected fish (22 study units). The most commonly
collected invertebrate was asiatic clams (17 study units).
Table 3. Number of samples by species and study unit
(species with 10 or more samples).
Summary statistics for the trace-element concentrations
(and percent moisture) in tissue samples are shown in table 4; this table shows
maximum, minimum, and median concentrations for each trace element, in addition
to the number of observations. These summary
statistics are reported for the most common species-tissue type combinations. Multiple
samples at a given site are each given equal weight in the summary statistic
calculations. These observed concentrations can be used as a guide for expected
concentrations in tissue samples from rivers and streams in the United States.
Table 4. Summary statistics for element
concentrations and percent moisture for most common species-tissue types.
Interpretations of the data presented here are beyond the scope
of this report. These data serve as a
library of information that others can use to compare trace-element
concentrations in tissues of aquatic organisms found in other studies.
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U.S. Department of the Interior |
U.S. Geological Survey