East Big Creek IA 02-CED-503

Assessment Comments

This assessment was historically based on 2001 IDNR/SHL biological sampling data (see below). These data are now too old (greater than 10 years) to accurately characterize this waterbody.

Basis for Assessment

This assessment was historically based on 2001 IDNR/SHL biological sampling data (see below).   These data are now too old (greater than 10 years) to accurately characterize this waterbody.

[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 (2012) 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" due to the lack of information upon which to base an assessment.   The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supporting" based on results of IDNR/SHL biological sampling in 2001.   Because the data upon which this assessment is based are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively low confidence).  

EXPLANATION:  The Class B(WW2) aquatic life uses remains assessed (evaluated) as “fully supporting” based on data collected in 2001 as part of the IDNR/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 (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 2001 FIBI score was 72 (excellent) and the BMIBI score was 75 (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 for previous Section 305(b) reports.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The riffle habitat FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70.  

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a five-year period.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.