Bear Creek IA 02-IOW-701

Assessment Comments

Assessment based on results of IDNR/UHL biological (biocriteria) monitoring in 1999: Fish IBI= 49 (fair); partial results for macroinvertebrate monitoring suggest impairment..

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 to "monitored." Thus, partial results from monitoring of benthic macroinvertebrates in 1999 indicates impairment (I.e., "partial support") of aquatic life uses that is now appropriate for addition to Iowa's 2004 Section 303(d) list, and this waterbody was moved from IR Category 2b to 5b.   Iowa DNR’s original assessment for the 2004 Section 305(b) assessment cycle is included below.]

SUMMARY:  The Class B(LR) aquatic life uses are assessed (evaluated) as "fully supporting / threatened" (minor impacts) based on results of IDNR/UHL biological (biocriteria) sampling in 1999.   This is the same assessment as that developed for the 2002 reporting cycle.

EXPLANATION:  This assessment was based on data collected in 1999 as part of the DNR/UHL stream biocriteria 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).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 Fish IBI score was 49 (fair).   The benthic macroinvertebrate sampling results were incomplete; thus, the assessment category is considered "evaluated."  But the partial results suggested that benthic community integrity might be impaired.  Additional follow-up benthic sampling should be done to support a more complete assessment of aquatic life use status.   Until additional sampling data are available, the aquatic life use support is assessed as fully supporting / threatened (=FST), based on a comparison of the F-IBI score 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.