Little Waterman Creek IA 06-LSR-1621

Assessment Comments

Assessment remains based on results of IDNR/UHL biological (biocriteria) monitoring in 2002: FIBI = 42 (fair), BMIBI = 45 (fair). FIBI BIC = 43, BMIBI BIC = 54.

Basis for Assessment

[Note:  Prior to the current (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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 (2008) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW2) aquatic life uses remain assessed (monitored) as "partially supported" based on results of IDNR/UHL biological (biocriteria) sampling in 2002.   This assessment changed from the 2006 assessment of "fully supporting" to the 2008 "partially supporting" because the BMIBI score was previously calculated incorrectly due to a programming or watershed delineation error.   The BMIBI score changed from a 46 to a 45 and went from meeting the BMIBI BIC (using the UAV of 8 points) to being one point below the BMIBI BIC.    

EXPLANATION:  The assessment of the presumptive Class B(WW1) aquatic life uses remains based on data collected in 2002 as part of the DNR/UHL stream biocriteria project.  The 2002 FIBI score was 42 (fair) and the BMIBI score was 45 (fair).   The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54.   Even though this site passed the FIBI BIC (using the FIBI UAV of 7 points) and failed to meet 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.  

This assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for headwater streams.   Prior to the changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions.   IDNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow.   The aquatic environment of most headwater streams is one of extremes in water quality.   Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow.   Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams.   For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report).   The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence).   Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.