Prairie Creek IA 01-MAQ-32

Assessment Comments

Assessment based on 2008, 2009 and 2010 IDNR/SHL biological sampling data: 63, 65 (both good) and 78 (excellent); BMIBI = 51, 55 (both fair) and 59 (good). FIBI BIC = 36; BMIBI BIC = 51.

Basis for Assessment

Note:  Prior to the 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, 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 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 remain "not assessed" (IR 3a due to the lack of data for indicator bacteria upon which to base an assessment.   The Class B(WW2) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of IDNR/SHL biological sampling from 2008-2010.  

EXPLANATION:  The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on data collected in 2008, 2009 and 2010 as part of the IDNR/SHL 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 2008 FIBI score was 65 (good) and the BMIBI score was 51 (fair).   The 2009 FIBI score was 78 (excellent) and the BMIBI score was 59 (fair).   The 2010 FIBI score was 63 (good) and the BMIBI score was 55 (fair).   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.   This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 3/3 times in the most recent five year period.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.

This assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years from 2008-2012.