Little Sioux River IA 06-LSR-1577

Assessment Comments

F-IBI score was 57 (good) and the BM-IBI score was 69 (good). The aquatic life use support was assessed as fully supported / threatened (=FST),

Basis for Assessment

The assessment was based on data collected in 1996 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) 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) to 100 (maximum).

The F-IBI score was 57 (good) and the BM-IBI score was 69 (good).   The aquatic life use support was assessed as fully supported / threatened (=FST), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2000 Section 305(b) report.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-1998.

Based on this biological assessment, the causes of the threats to full support of the Class B(WW) uses were identified as (1) un-ionized ammonia, (2) nutrients, (3) organic enrichment/low DO, and (4) other habitat alterations.   The sources of these threats were all related to agricultural practices (pasture grazing, grazing of riparian areas, and intensive animal feeding operations).