Assessment Comments
Assessment is based on statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000). Potential causes & sources of impairment were applied to all sites in study.
Basis for Assessment
Segment not assessed for Section 305(b) reports prior to 2002.
SUMMARY: The Class A (primary contact recreation) uses are "not assessed." The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported" based on results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams. The fish consumption uses are "not assessed." EXPLANATION: The Class A (primary contact recreation) uses are "not assessed" due to the lack of information on levels of indicator bacteria in this river segment. The Class B(WW) uses are assessed (evaluated) as "partially supported" based on information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000). 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 one sample site in this stream segment were 13 in the 1984-85 period and was 1 in the 1998-99 period for an average percent change of 92%. Based on these results, the aquatic life use are assessed as "partially supported." 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. Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairment of these uses that may exist. Fish consumption uses are "not assessed" due to the lack of fish contaminant monitoring in this river segment.
