Dutton Creek IA 01-TRK-6285

Assessment Comments

Assessment based on 2007 IDNR/UHL biological monitoring data: WW BMIBI = 84, 85 (excellent) and CBI = 65, 76. Both the warm and cold water assessments suggest full support.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses.   According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters.   Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.   This waterbody had not been assessed for Section 305(b)/303(d) purposes prior to the 2008 assessment/listing cycle.]

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 presumptive Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" based on results of IDNR/SHL biological monitoring in 2007.  

EXPLANATION:  The assessment of the presumptive Class B(WW1) aquatic life uses remains based on data collected in 2007 as part of the IDNR/SHL stream REMAP 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 2007 BMIBI score was 85 (excellent) and the 2011 BMIBI score was 84 (excellent).   Fish were not collected in this segment.   The aquatic life use support was assessed (monitored) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The BMIBI BIC for this ecoregion is 61.   Even though this site passed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.  

The 2007 sampling data suggest that this stream is a coldwater stream.   However, until a Use Attainability Assessment can be completed, the presumptive designated uses for this stream are the presumptive Class A1 (primary contact recreation) and Class B(WW1) aquatic life.   Below you will find the cold water assessment for this segment.  

The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007 and 2011 as part of the IDNR/SHL coldwater stream sampling project.   A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach.   The biological metrics were combined to make a coldwater benthic index (CBI).   The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2007 CBI score was 76 and the 2011 CBI score was 65.  The aquatic life use support was assessed (monitored) as fully supporting (=FS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 2/2 times in the last 5 years.