Odebolt Creek IA 06-LSR-1592

Assessment Comments

Assessment remains based 1997 IDNR/UHL biological monitoring data: FIBI = 42, 34 (fair); BMIBI = 58, 59 (good). FIBI BIC = 31, BMIBI BIC = 54. Due to the age of the biological data (> 10 years), the assessment of the aquatic life uses is changed from "fully supported" (evaluated) to not assessed.

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 (see http://www.iowadnr.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 (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.   Due to the age of the biological data upon which the assessment is based, the assessment of the Class B(WW2) aquatic life uses is changed from "fully supported" (evaluated) to not assessed.   The previous assessments were based on results of IDNR/UHL biological (biocriteria) sampling in 1997.  

EXPLANATION:  For previous assessment/listing cycles, the assessment of the Class B(WW2) aquatic life uses (fully supporting/evaluated) was based on data collected in 1997 as part of the IDNR/UHL stream biocriteria project.   Sampling was conducted at two sites on this stream segment.   The FIBI scores were 42 and 34 (both in the "fair" category); the BMIBI scores were 58 and 59 (both good).   The aquatic life use support was assessed (evaluated) as fully supported (=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 1994-2004.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI and BMIBI BICs 2/2 times in 1997.  

Due to the age of the data used for this assessment (greater than 10 years), the previous (2010) assessment of the Class B(WW2) aquatic life uses is changed from “fully supporting” to “not assessed” due to age of the data upon which the assessment was based.   As water quality data age, they are less able to represent current water quality conditions.   As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect.   Additional monitoring is needed in this assessment segment to update status of its aquatic communities.