Wapsipinicon River IA 01-WPS-346

Assessment Comments

USGS/NAWQA fish tissue and water quality monitoring near Tripoli.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment IA 01-WPS-0020-1, which extended 108 miles from the confluence with Buffalo Creek at Anamosa to Snyder Access in Bremer County, was split into seven subsegments:  (1) Buffalo Creek at Anamosa to Walton Creek  in Linn County (IA 01-WPS-0020-1), (2) Walton Creek to Pine Creek in Buchanan Co.  (IA 01-WPS-0020-2), (3) Pine Creek to Harter Creek in Buchanan Co.  (IA 01-WPS-0020-3), (4) Harter Creek to L.  Wapsipinicon River in Buchanan Co.  (IA 01-WPS-0020-4), (5) L.  Wapsipinicon River to Crane Creek in Black Hawk Co.  (IA 01-WPS-0020-5), (6) Crane Creek to East Fork Wapsipinicon River in Bremer Co.  (IA 01-WPS-0020-6), and (7) East Fork Wapsipinicon River to Snyder Access in Bremer Co.  (IA 01-WPA-0020-7).   See assessment information for segment IA 01-WPS-0020-1 (Buffalo Creek to Walton Creek, Linn Co.) for previous Section 305(b) assessments for this river reach.]

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "fully supported / threatened"; the fish consumption uses are "not assessed."  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 through September 2001 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05420608) and (2) 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 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 9 samples collected from January through September 2001 and (2) no violations of the Class B(WW) chronic water quality criterion for pesticides in the 9 samples analyzed during this period.   Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams, however, suggest a potential threat to 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).   In general, this comparison showed sharp declines in the numbers of mussel species ("species richness") from the mid-1980s to the late 1990s.   For purposes of Section 305(b) reporting, 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.   This assessment included the following factors:  (1) the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey and (2) the number of mussel species found in the 1998-99 survey.   Greater than a 50% decline in species richness from the 1984-84 to the 1998-99 period suggests an impairment of the aquatic life uses.   In addition, low species richness in the 1998-99 survey suggests potential impairment.   For purposes of Section 305(b) assessment only, staff of the IDNR Water Quality Bureau used results from Arbuckle et al.  (2000) to define categories of species richness for Iowa's mussel communities:  less than three species indicates low species richness and "nonsupport" or "partial support" of aquatic life use; from four to seven species indicates moderate species richness and potential minor impacts (="fully supported / threatened"); more than seven species indicates high species richness and "full support" of 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 for an average percent change of only -8%.   The comparison of species richness between the 1984-85 and 1998-99 periods thus suggest relatively little change in the mussel community of this stream segment.   Based on these results, and based on the assessment framework described above, the "full support" of aquatic life uses suggested by results of USGS ambient monitoring is downgraded slightly to "fully supported / threatened."  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 instream 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 "not assessed" due the lack of recent fish contaminant monitoring in this river segment.   The previous assessment of fish consumption uses for this river segment ("fully supported") was based on results of the USGS/NAWQA fish tissue monitoring in September 1995 (see assessment for the 1998 report above).   These data are now considered too old (greater than five years) for characterizing current water quality conditions.