Assessment Comments
Assessment remains based on results of 1997 IDNR/SHL biological sampling data: FIBI = 20 (poor), BMIBI = 41 (fair). Non-riffle habitat FIBI BIC = 32, BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) 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 presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR 3b-c) based on results of IDNR/SHL biological sampling in 1997.
EXPLANATION: The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supporting” based on data collected in 1997 as part of the IDNR/SHL stream biological sampling 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 2003 FIBI score was 20 (poor) and the BMIBI score was 41 (fair). 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 1994-2008. The non-riffle FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment failed both the FIBI and BMIBI BICs in 1997.
This assessment is considered "evaluated" because there were not two or more samples collected in multiple years from 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).
In addition, the data upon which this biological assessment is based are now more than ten years old. As water quality data age, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasingly suspect. Despite the age of these data, the aquatic life uses of this assessment segment will remain “partially supporting/evaluated” and will remain on Iowa’s list of waters in need of further investigation (IR Category 3b-c). Additional monitoring is needed in this assessment segment to update status of its aquatic communities.
