ADBNet

Assessment Comments

1997 Biocriteria: Fish IBI=23(poor), BM-IBI=57(good).

Basis for Assessment

The DNR/EPD stream assessment project data collected in 1991 were not used to determine the degree of aquatic life use support for this waterbody segment because the data are more than five years old, and no longer considered current.   The assessment was based on data collected in 1997 as part of the DNR/UHL stream biocriteria development project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.    The biological metrics were combined to make a fish community index of biotic integrity (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum)-100 (maximum).  

The F-IBI score was 23(poor), and the BM-IBI score was 57(good).   The aquatic life use support status was assessed as partially supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2000 Section 305b report (IDNR 2000).   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-1998.  

Despite having moderate richness of fish species, the community index ranking was poor because the majority of fish were tolerant/habitat generalists, primarily consisting of minnow species; sensitive species were absent, and habitat specialists were present in very low numbers.  The "good" rating obtained for the benthic macroinvertebrate index suggests that water quality at the time of the assessment was acceptable, and capable of supporting a more balanced and diverse fish community.   The habitat assessment rating was in the "fairly good" range suggesting habitat is capable of supporting a better fish community.   However, several suboptimal habitat characteristics were observed.   The dominant type of substrate was sand, and the channel was relatively wide and shallow.   Several sediment bars and areas of raw, eroding banks were noted.   The riparian zone at the sampling site was relatively undisturbed, suggesting that sediment and channel erosion sources originate further upstream in the watershed.  It is possible that long-term changes in the watershed hydrology and stream channel morphology of the stream have adversely impacted the habitat for fish populations.   Additional assessment information is needed to determine the magnitude and extent of impairment.   The length of stream that was sampled (<0.25 mile) is very small in relation to the waterbody segment length (28 miles).   More assessment data are needed to adequately characterize aquatic life uses throughout the entire segment.   Follow-up sampling is needed to determine whether the 1997 sampling results are representative of the fish community.