Wapsipinicon River IA 01-WPS-346

Assessment Comments

Assessment is based on results of (1) monitoring conducted on Wapsipinicon River near Tripoli from (a) March 1996 through September 1998 and (b) from January 2001 through August 2002 as part of the USGS NAWQA study, (2) results of fish contaminant monitoring conducted in 1995 as part of the NAWQA program, and (3) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998-99.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation uses) are “not assessed” due to lack of data for indicator bacteria upon which to base an assessment.   The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported."  The fish consumption uses remain assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1995.   The sources of information for this assessment include (1) the results of monitoring conducted on Wapsipinicon River near Tripoli from (a) March 1996 through September 1998 and (b) from January 2001 through August 2002 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05420608), (2) results of fish contaminant monitoring conducted in 1995 as part of the USGS NAWQA program, and (3) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998-99.  

EXPLANATION:  Similar to results of USGS monitoring from 1996 through 1998, the results of USGS NAWQA monitoring in 2001 and 2002 suggest "full support" of the Class B(WW) aquatic life uses.   This monitoring showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the approximately 20 samples collected from January 2001 through August 2002 and (2) no violations of the Class B(WW) chronic water quality criterion for pesticides in the 19 samples analyzed during this period.  

Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams suggest “full support” of the aquatic life uses of this stream segment.   As part of this study, sampling results from 1998 and 1999 (Arbuckle et al.  2000) were compared to results from stream sites surveyed in 1984 and 1985 by Frest (1987).   On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s streams and rivers from the mid-1980s to the late 1990s.   Results of this comparison were used by staff of the Iowa DNR Water Quality Bureau to assess the degree to which the aquatic life uses of the sampled stream segments are supported.   For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey.   Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggests an impairment of the aquatic life uses.   Species richness of freshwater mussels at the three sample sites in this stream segment were 8, 6, and 4 in the 1984-85 period and were 6, 6, and 4, respectively, in the 1998-99 period.   The species richness between the 1984-85 and 1998-99 periods is similar at these sites, with an average decline of only minus 8%.   Thus, based on IDNRs assessment approach, these results do not suggest impairment of the aquatic life uses.   This is one of the few river/stream segments sampled by Arbuckle et al.  (2000) that did not show significant declines in species richness between the 1984-85 period and the 1998-99 period.    As presented by Arbuckle et al.  (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high in-stream levels of nutrients (phosphorus and nitrogen).   Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness.  

Fish consumption uses are assessed (evaluated) as “fully supported” based on results of the USGS/NAWQA fish tissue monitoring in September 1995 (see assessment for the 1998 report).   However, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively lower confidence).