Assessment Comments
Assessment remains based on 2003 and 2008 IDNR/SHL biological sampling data: FIBI = 33, 34, 44 (fair); BMIBI = 33, 40, 44 (fair). FIBI BIC = 32 (non-riffle), 53 (riffle); BMIBI BIC = 62.
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 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" (IR 3a) due to the lack of information upon which to base an assessment The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supported” (IR 5b-t) based on biological monitoring data collected in 2003 and 2008. This assessment remains in Category 5b-t of Iowa’s Integrated Report (on Iowa’s Section 303(d) list).
EXPLANATION: The Class B(WW2) aquatic life uses remain assessed (evaluated) as “partially supported” based on biological data collected in 2003 and 2008 as part of the IDNR/SHL stream biocriteria and follow-up sampling projects. 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 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 2003 FIBI scores were 34 (fair); 33 (fair) and the BMIBI scores were 33 (fair); 44 (fair). The 2008 FIBI score was 44 (fair) and the BMIBI score was 40 (fair). The aquatic life use support was assessed as partially supporting (=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 1994-2008. The FIBI BIC for this ecoregion is 32 (non-riffle) and 53 (riffle) and the BMIBI BIC for this ecoregion is 62. The 34 and 44 FIBI scores correspond with a non-riffle site and passed the non-riffle BIC (32), while the 33 FIBI score was from a riffle site, thus it failed to meet the riffle BIC (53). In addition, all sites failed to meet the BMIBI BIC of 62. This segment passed the FIBI BICs 2/3 times and passed the BMIBI BIC 0/3 times in the past 10 years.
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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 10 years (2003-2012); however, the multiple samples were not collected during 2008-2012. 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). However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s Section 303(d) list of impaired waters.
