Assessment Comments
Assessment based on results of (1) IDNR/UHL biocriteria sampling in 2001 and (2) statewide survey of freshwater mussels in 1998-99 (Arbuckle et al. 2000).
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as "fully supported" based on results of IDNR/UHL biological monitoring in 2001. Results from the 1998-99 statewide survey of freshwater mussels suggests "full support" of aquatic life uses, as well.
EXPLANATION: The assessment was based on data collected in 2001 as part of the DNR/UHL stream biocriteria project. The 2001 FIBI score was 67 (good) and the BMIBI score was 78 (excellent). The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The riffle site FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70.
This segment of Deer Crek was sampled as part of the 1998-99 statewide study of freshwater mussels in Iowa streams and rivers (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). On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa streams and rivers from the mid-1980s to the late 1990s. For stream segments having four or more species reported for the 1984-95 survey, 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. The results of this sampling on Deer Creek, however, showed an increase in species richness between the 1984-98 and 1998-99 survey peirods. Species richness of freshwater mussels at the one sample site in this segment was 7 in the 1984-85 period and was 12 in the 1998-99 period, respectively, for a percent change of plus 71%. These results also suggest "full support" of the aquatic life uses.
