Assessment Comments
Assessment based on 2002 REMAP data: Fish IBI = 13 (Poor).
Basis for Assessment
[NOTE: The IDNR assessment methodology for biological data was changed in Fall 2005 during U.S. EPA's review of Iowa's 2004 Section 303(d) list such that only one of the two IBI scores for target groups (fish and aquatic macroinvertebrates) is now needed for a "monitored" assessment. Previously, the IDNR methodology required that IBI values for both target groups be present in order for an assessment to be considered "monitored" (of higher confidence); if only one of the two IBIs was available, the assessment was considered "evaluated" and of lower confidence. Based on this revision in methodology, the assessment type for this assessment was changed from "evaluated" to "monitored." Thus, the F-IBI score of 13 (poor) from biological monitoring in 2002 indicates impairment that is now appropriate for addition to Iowa's 2004 Section 303(d) list, and this waterbody was moved from IR Category 3b to 5b.]
The assessment was based on data collected in 2002 as part of the DNR/UHL REMAP 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 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). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 Fish IBI score was 13 (Poor). The aquatic life use support was assessed as Not Supporting (=NS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
As part of the 2002 REMAP project, stream physical habitat assessment found significant channel alterations that could contribute to the biological impairment. These include, bank instability, channel widening, shallow water depth, and excessive sediment bar development. Elevated summer water temperature (33.4C) and low D.O. levels at night (4.7 mg/L) were observed. Channel alterations, which have increased the stream width:depth ratio (38.4), probably have also contributed to adverse water quality conditions.
