Assessment Comments
Assessment remains based on 2001 and 2006 IDNR/UHL biological monitoring data: 2001 FIBI = 48 (fair) and 2006 FIBI = 57 (good), 2006 BMIBIs = 26 (poor) and 38 (fair). Riffle-habitat FIBI BIC = 53, 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, 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 (2012) 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" 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” based on results of IDNR/UHL biological (biocriteria) sampling in 2006.
EXPLANATION: The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supporting” based on biological data collected in 2001 and 2006 on Big Cedar Creek approximately 7 mile NNE of Fonda in Pocahontas County as part of the IDNR/UHL stream biocriteria project. 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 that were 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 48 (fair). The 2006 FIBI score was 57 (good) and the BMIBI scores were 26 (poor) and 38 (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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The riffle site FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 1/2 times in the last 10 years and failed the BMIBI BIC 2/2 times in 2006.
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 (2001-2010); however, the samples were not collected during a five year period (2006-2010) and/or were not collected in multiple years. 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).
Prior to the changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this stream was classified only for general uses due to the inability of the stream to support a viable aquatic community at low-flow conditions. IDNR’s existing biological assessment protocol, however, was calibrated to aquatic life reference conditions in larger wadeable streams with perennial flow. The aquatic environment of most headwater streams is one of extremes in water quality. Consequently, intermittent headwater streams tend to have biological diversity that is low relative to more stable aquatic environments of larger streams with perennial flow. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse streams will likely overstate the existence of impairment in headwater streams.
