Assessment Comments
Assessment is based on results of IDNR/UHL biological (REMAP) monitoring in 2002: FIBI = 27 (fair). FIBI BIC = 36.
Basis for Assessment
SUMMARY: The general aquatic life uses are upgraded to "partially supported" (evaluated) based on results of IDNR/UHL biological (REMAP) sampling in 2002. Due to an error in the watershed size determination at this site, the 2002 FIBI score (24) used for the 2006 assessment was incorrect. The 2002 FIBI score is now a 27 and the assessment upgraded to "partially supporting", this segment remains in category 3b of the IR.
EXPLANATION: This evaluated biological assessment was based on data collected in 2002 as part of the DNR/UHL stream REMAP project. A series of biological metrics that 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 fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity. The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 FIBI score was 27 (fair). The aquatic life use support was assessed (evaluated) as Partially Supporting (=PS), 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 FIBI BIC for this ecoregion is 36. Even though this site failed to meet the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small general use stream and doesn’t fall in the calibrated watershed size.
As part of the 2002 REMAP project, stream physical habitat assessment found significant levels of silt, a lack of instream cover, and eroding stream banks that contribute to the biological impairment. Natural fluctuations in flow and aquatic habitat conditions that would be expected in a stream with a small watershed area might also contribute to aquatic life impairment.
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”.
