Assessment Comments
Assessment remains based on 2002 IDNR/SHL biological sampling data: FIBI = 13 (poor). FIBI BIC = 33.
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 (evaluated) as “not supporting” (IR 5b-t) based on biological data collected in 2002 as part of the IDNR/SHL stream REMAP biological sampling project. 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 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). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 FIBI score was 13 (poor) and the density of macroinvertebrates on the sampling gear was too low to calculate a BMIBI. The aquatic life use support was assessed as not supporting (=NS), based on a comparison of the FIBI score 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 33 and this segment failed the FIBI BIC using the single 2002 sample.
As part of the 2002 REMAP project, stream physical habitat assessment found significant channel alterations that could contribute to the biological impairment. These include, bank instability, channel widening, shallow water depth, and excessive sediment bar development. Elevated summer water temperature (33.4C) and low D.O. levels at night (4.7 mg/L) were observed. Channel alterations, which have increased the stream width:depth ratio (38.4), probably have also contributed to adverse water quality conditions.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over a five-year period. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). 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 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 was previously on Iowa’s Section 303(d) list and thus remains on Iowa’s Section 303(d) list of impaired waters (IR Category 5b-t).
