Assessment Comments
Assessment remains based on results of IDNR/UHL biological (biocriteria) monitoring in 1997: FIBI = 33 (fair), BMIBI = 70 (good). FIBI BIC = 43, BMIBI BIC = 54.
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.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 (2010) 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. The Class B(WW-2) aquatic life uses remain assessed (evaluated) as partially supported based on results of IDNR/UHL biological (biocriteria) sampling in 1997. The 1997 sampling data are now greater than five years old; therefore, this assessment is now considered "evaluated" instead of "monitored".
EXPLANATION: The aquatic life uses remain assessed (evaluated) as "partially supporting" based on results of the IDNR/UHL biocriteria monitoring conducted on this stream segment in 1997. The FIBI score was 33 (fair); the BMIBI score was 70 (good). The aquatic life use support was assessed (evaluated) as partially supported (=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 FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
The IDNR placed this segment in Category 4c instead of 3b or 5b for the following reasons:
1) the data are now more then five years old and are now unreliable for determining the current biological condition;
2) the benthic macroinvertebrate data indicate good water quality and score 16 points higher than the ecoregion BMIBI BIC and;
3) even though the fish data score marginally lower than the ecoregion FIBI BIC, after evaluating the habitat data, it was concluded that habitat alterations/hydromodification most likely led to the decreased FIBI scores.
