Prairie Creek IA 01-MAQ-32

Assessment Comments

Assessment based on 2006 TMDL sampling data: FIBI = 75 (excellent), 41 (fair); BMIBI = 53 (fair), 71 (good). FIBI average = 58, BMIBI average = 62. FIBI BIC = 36; BMIBI BIC = 51.

Basis for Assessment

Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses.    Due to changes in Iowa’s surface water classification that were approved by U.S.   EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses.    The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses).    Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of data for indicator bacteria upon which to base an assessment.   The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of IDNR/UHL biological (biocriteria) monitoring in 2006.

EXPLANATION:  This aquatic life assessment was based on data collected in 2006 as part of the DNR/UHL stream TMDL follow-up sampling project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2006 FIBI scores were 75 (excellent), 41 (fair) and the BMIBI scores were 53 (fair), 71 (good).   The FIBI average was 58 (good) and the BMIBI average was 62 (good).   The aquatic life use support was assessed as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.   The FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.