West Fork Cedar River IA 02-WFC-802

The Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supporting" based on biological data collected in 2006 and 2012 as part of the DNR/SHL 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 2006 FIBI score was 65 (good) and the BMIBI score was not available due to flooding removing the artificial substrates. The 2012 FIBI score was 70 (good) and the BMIBI score was 54 (fair). The aquatic life use support was assessed as fully supporting (=FS), 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 1994-2008. The non-riffle site FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC is 52. This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 1/1 times in the last 11 years. This assessment is considered evaluated because the drainage area (554 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 passed 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 DNR assessment methodology. DNR now requires a segment have two or more biological samples collected from the segment in multiple years over a recent five-year period to be considered “monitored”. This segment had multiple FIBI samples collected in the previous 11 years (2006-2016); however, the multiple samples were not collected during the recent five-year period. Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring near Allison, Iowa, in 2011 and 2012. In the 2011 samples, the composite samples of fillets from channel catfish had low levels of contaminants: mercury: 0.136 ppm; total PCBs: 0.091 ppm; and technical chlordane: <0.03 ppm. The average level of mercury in the tissue plugs from four smallmouth bass, however, was 0.415 ppm (SD=0.099 ppm). This level exceeded the threshold for a one-meal per week consumption advisory. According to Iowa’s fish consumption advisory protocol, however, two consecutive samplings that show contaminant levels above the advisory threshold are needed to confirm that an advisory should be issued. Thus, follow-up sampling was conducted in 2012. The results of this follow-up sampling showed that the average level of mercury in the tissue plugs from four smallmouth bass (0.182 ppm; SD=0.077 ppm) was well below the advisory threshold of 0.3 ppm, thus suggesting no justification for issuance of a consumption advisory for this river segment. These results suggest continued full support of the fish consumption uses.