Drainage Ditch 71 IA 03-SSK-963

Assessment Comments

Assessment is based on (1) 1997 DNR/UHL bioassessment (Fish IBI= 20 (poor), BM-IBI= 42 (fair)) and (2) occurrence of a fish kill in August 1999.

Basis for Assessment

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 20 (poor), and the BM-IBI score was 42 (fair).   The aquatic life use support status was assessed as not supporting (=NS), 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.   A fish kill occurred on DD-71 on August 19, 1999 at the north side of Jewell in Hamilton County.   This kill was attributed to agricultural fertilizer:  a brief, hard rain washed a slug of ammonia into DD-71.   Approximately ½ mile of stream was affected; an estimated 9,300 fish were killed (an additional kill occurred in DD-71 near Jewell on August 7, 1995 (see above)).   According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period (1997-1999) indicates that the aquatic life uses of a waterbody are only "partially supported."  The assessment based on results of DNR/UHL biocriteria sampling ("not supported"), however, is more restrictive; thus, the final assessment of the general aquatic life uses is "not supported."