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
[Note: For the 2002 report, the previous waterbody segment IA 02-CED-0540-0, which extended 12 miles from the mouth of Deer Creek to an unnamed tributary in Worth County, was split into two subsegments: (1) mouth to the Mitchell-Worth county line. (IA 02-CED-0540-1) and (2) Mitchell-Worth county line to confluence with an unnamed tributary at east line of S28, T100N, R19W, Worth Co. (IA 02-CED-0540-2). See assessment information above for previous Section 305(b) assessments for the previous 12-mile stream segment.]
SUMMARY: The Class B(LR) aquatic life uses remain assessed (monitored) as "fully supported / threatened" 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.
EXPLANATION: The assessment was based on data collected in 2001 as part of the DNR/UHL stream biocriteria project. The 2001 Fish IBI score was 68 (good) and the BM-IBI score was 77 (excellent). The aquatic life use support was assessed as fully supporting/threatened (=FST), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
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 suggest "full support" of the aquatic life uses. The assessment of the aquatic life uses, however, will remain based on the results of the more traditional biological monitoring conducted in this segment in 2001 (i.e., multi-metric fish / benthic macroinvertebrate indexes of biotic integrity).
