Assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring in 2002, 2003 and 2004 and (2) IDNR/UHL ambient monthly monitoring near Mapleton from 2002-04.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported” based on results of biological monitoring in 2002, 2003, and 2004. Results of ambient water quality monitoring from 2002 through 2004 suggest relatively good water quality in this river segment. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. This assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring conducted in 2002, 2003, and 2004 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2002-2004 assessment period at the Highway 141-175 bridge at Mapleton (STORET station 10670002 (formerly station 911040)).
EXPLANATION: Results of ambient chemical/physical monitoring at the IDNR/UHL station at Mapleton showed no violations of Class B(WW) water quality criteria during the 2002-2004 assessment period for dissolved oxygen (minimum value = 7.1 mg/l), ammonia nitrogen (maximum value = 0.84 mg/l) or pH (range = 7.8 to 8.5 units). Levels of pesticides in the seven samples analyzed, and levels of toxic metals in the ten sampled analyzed, were all below the analytical level of detection. These results suggest “full support” of the Class B(WW) aquatic life uses.
Despite results of ambient physical/chemical monitoring that suggest “full support” of aquatic life uses, results of biological monitoring suggest only “partial support” of these uses. This assessment was based on biological data collected in 2002, 2003, and 2004 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 2002 BMIBI score was 46 (fair). The 2003 FIBI score was 9 (poor) and the 2003 BMIBI score was 55 (fair). The 2004 FIBI score was 14 (fair) and the 2004 BMIBI score was 50 (fair). The FIBI average was 11.5 and the BMIBI average was 50.3. 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 FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54. This assessment is considered “evaluated” because the drainage area (734 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. 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 "not assessed due to the lack of recent fish contaminant monitoring in this river reach.