Assessment Comments
Assessment remains based on 2010 and 2011 IDNR/SHL biological sampling data: FIBI = 32, 39 (fair) and BMIBI = 27 (poor) and 43 (fair). FIBI BIC = 33 and BMIBI BIC = 41.
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/EXPLANATION: 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 (monitored) as “partially supporting” (IR 5b-t).
This aquatic life assessment was based on 2010 and 2011 IDNR/SHL biological sampling data. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 2010 and 2011 FIBI scores were 32 and 39 (fair) and the BMIBI scores were 27 (poor) and 43 (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 FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This segment passed both the FIBI and BMIBI BICs 1/2 times in 2010 and 2011. The biological impairment criteria were determined from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.
This assessment is considered "monitored" because there were two or more samples collected from this segment in multiple years. However, this segment should have been place in Category 3b-c for the 2012 cycle because the data collected in 2011/2012 were inconclusive regarding the aquatic life support level in this segment. However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b-t and remains on Iowa’s 2010 Section 303(d) list of impaired waters. Additional monitoring is needed in this assessment segment to update status of its aquatic communities.
