Des Moines River IA 04-UDM-1223

The Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supporting” based on biological data collected in 2005 as part of the IDNR/SHL 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 1994-2008. 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 segment failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size.

This aquatic life assessment is now also 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 2010 and 2014 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 are assessed (monitored) as “partially supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring in 2009 and 2010. The fish contaminant data generated from the 2009 RAFT sampling conducted at the West Fork Des Moines River near Bradgate showed that levels of mercury were sufficiently high for concern and thus justified follow-up monitoring. Results from the 2009 sampling showed that the level of mercury in the sample of walleye fillets (0.328 ppm) exceeded the 1 meal/week trigger level (0.30 ppm) as defined in Iowa’s fish consumption advisory protocol. According to IDNR’s assessment methodology, the single occurrence of contaminant above an advisory trigger level neither warrants issuance of an advisory nor indicates impairment of the fish consumption uses: two consecutive samplings that show contaminant levels are above the trigger level in fillet samples are needed to justify issuance of an advisory. Follow-up sampling conducted in 2010 showed that levels of mercury in walleye (0.37 ppm) again exceeded the 1 meal/week trigger level (0.30 ppm). Thus a one meal per week fish consumption advisory was issued for West Fork Des Moines River that extends from the confluence of the East Fork and West Fork of the Des Moines River upriver to Highway 15 south of West Bend, Iowa. Because this advisory includes approximately half of this 14-mile assessment segment, the fish consumption uses are assessed as if the advisory extended through the entire segment. The existence of the consumption advisory for this segment of the West Fork Des Moines River indicates that the fish consumption uses should be assessed as “partially supporting”.