Assessment Comments
Assessment remains based 2001, 2005 and 2008 IDNR/SHL biological sampling data: FIBI = 5 (poor), 44 (fair), 51 (good); BMIBI = 10 (poor), 59, 63 (good). FIBI BIC = 43, BMIBI BIC = 54.
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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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 are assessed (evaluated) as “partially supporting” (IR 5b-t) based on data collected in 2001, 2005 and 2008 as part of the IDNR/SHL stream biocriteria and REMAP projects. 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 2001 FIBI score was 51 (good) and the BMIBI score was 63 (good). The 2005 FIBI score was 5 (poor) and the BMIBI score was 59 (good). The 2008 FIBI score was 44 (fair) and the BMIBI score was 10 (poor). 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 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI and BMIBI BICs 2/3 times in the last 12 years. This satisfies the IDNR methodology to be considered "fully supporting". However, IDNR decided that the two failing scores were too low to declare this segment fully supporting its' aquatic life uses and declared this segment "partially supporting". The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.
This aquatic life assessment is now considered "evaluated" because there were not two or more samples collected from this segment in multiple years in a recent five year period. 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 2014 Section 303(d) list of impaired waters.
