Tipton Creek IA 02-IOW-755

Assessment Comments

Assessment based on results of IDNR/UHL biological (biocriteria) monitoring in1999: Fish IBI= 51 (good), BM-IBI= 61 (good).

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses are assessed (monitored) as "fully supported / 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) 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 1999 Fish IBI score was 51 (good) and the BM-IBI score was 61 (good).  The aquatic life use support was assessed as fully supporting/threatened (=FST), based on a comparison of the F-IBI and BM-IBI scores 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.

Although results of this and other biological assessments suggest that the Class B(LR) aquatic life uses of this segment of Tipton Creek are supported, the historic occurrence of fish kills suggests the potential for impacts to the aquatic life uses.   Fish kills occurred in this reach of Tipton Creek in August 1996 (46,000 fish estimated killed) and July 1998 (93,000 fish estimated killed over a 12-mile reach).   Both fish kills were caused by discharge of animal waste from animal feeding operations located near Williams, IA (the problems with repeated fish kills in Tipton Creek were highlighted in the August 1, 1998 Des Moines Register).   According to IDNR's assessment methodology, the absence of a fish kill in the three-year period following a fish kill suggest that impacts from the kill have dissipated.   And results of recent biological monitoring do suggest a recovery of the aquatic communities of this stream segment.   Thus, due to the lack of a kill in this stream reach since 1998, the occurrence of fish kills is no longer a factor in determining the degree to which the aquatic life uses are supported.