Iowa River IA 02-IOW-647

Assessment Comments

Assessment remains based on 2005 IDNR/UHL biological monitoring data: FIBI = 63 (good), 71 (excellent); BMIBI = 68, 71 (both good). FIBI BIC = 36, BMIBI BIC = 51.

Basis for Assessment

SUMMARY:  The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supporting” based on results of IDNR/UHL biological (REMAP) monitoring in 2005.   Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.

EXPLANATION:  The evaluated biological assessment of the Class B(WW1) aquatic life uses was based on data collected in 2005 as part of the IDNR/UHL stream REMAP project.   A series of biological metrics that 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 collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2005 FIBI scores were 63 (good), 71 (excellent) and the BMIBI scores were 68 (good), 71 (good).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 2/2 times (from both the 47b and 47f ecoregions).   This assessment is considered evaluated because the drainage area (748 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”.   This segment had multiple samples collected in 2005; however, the samples were not collected in multiple years.