Assessment Comments
Assessment based on 2000 IDNR/UHL biocriteria data: FIBI = 21 (poor), BMIBI = 31 (fair). Non-riffle habitat FIBI BIC = 32, BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the current (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.com/water/standards/files/06mar_swc.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 (2008) 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 are "not assessed" due to the lack of information upon which to base an assessment.
The Class B(WW-2) aquatic life uses remain assessed as "partially supported" based on results of biological monitoring in 2000. The full biological monitoring in 2000 suggests "partially supporting". Because of the segment's proximity to the upstream marsh, and the marsh-like qualities of the year 2000 site, it was determined to loosely apply the biological criteria and enter this assessment as evaluated. According to IDNR's assessment methodology, "evaluted" impairments are of relatively lower confidence that “monitored" which have relatively higher confidence. Such "evaluated" waters, while not appropriate for addition to Category 5 of the Integrated Report (= Section 303(d) list), 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”. In addition, the 2000 sampling data are now greater than five years old; therefore, this assessment is now considered "evaluated" instead of "monitored".
The assessment was based on data collected in 2000 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 2000 FIBI score was 21 (poor) and the BMIBI score was 31 (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 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 non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62.
