Assessment Comments
Assessment remains based on results of U.S. EPA/IDNR fish tissue monitoring in 2001 and 2005 IDNR/UHL stream REMAP biological sampling near West Bend.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is also now presumptively designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: Due to a lack of water quality information upon which to base assessments, the presumptive Class A1 (primary contact recreation) uses remain "not assessed.” The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on the 2005 stream REMAP biological sampling. Based on results of U.S. EPA / IDNR fish tissue monitoring in 2001 and on IDNR/UHL fish tissue monitoring conducted in 2005 for the REMAP project (Site 177), fish consumption uses remain assessed (monitored) as "fully supported."
EXPLANATION: The Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supporting” based on biological data collected in 2005 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 biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species 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 2005 FIBI score was 22 (poor) and the BMIBI score was 53 (fair). The aquatic life use support was assessed (evaluated) 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 riffle/non-riffle habitat FIBI BICs for this ecoregion are 53/32 and the BMIBI BIC for this ecoregion is 62. It is unknown at this time if this site had stable riffle habitat due to lack of quantitative physical habitat measurements; however, this site failed to meet either of the FIBI BICs and the BMIBI BIC. This assessment is considered evaluated because the drainage area (1,956 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2006 and 2010 to be considered “monitored”. This segment had a single sample collected in 2005. 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). According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Bradgate in 2001 and based on IDNR/UHL REMAP fish contaminant monitoring in 2005. The composite samples of fillets from channel catfish and walleye collected in 2001 had low levels of contaminants and did the composite sample of fillets in common carp collected in 2005. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.283 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm.
The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated from the 2001 RAFT and the 2005 REMAP samplings conducted in this segment of the Des Moines River show that the levels of contaminants do not exceed any of the IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.
