Assessment Comments
Assessment based on 2003 and 2007 IDNR/SHL biological sampling data: 2003 FIBI scores: 26 (fair), 20 (poor) and 2007 FIBI score was 35 (fair); 2003 BMIBI score was 38 (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 are "not assessed" (IR 3a) due to the lack of information upon which to base an assessment. The presumptive Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported" (IR 3b-u) based on the results of IDNR/SHL biological sampling in 2003 and 2007.
EXPLANATION: The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supported” (IR Cateogry 3b-u) based on results of biological sampling. This evaluated biological assessment was based on data collected in 2003 and 2007 as part of the IDNR/SHL stream biological monitoring project. A series of biological metrics that 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 2003 BMIBI score was 38 (fair). The 2003 FIBI scores were 26 (fair) and 21 (poor) and 2007 FIBI score was 36 (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 biological data collected at stream ecoregion reference sites from 1994-2008. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. This segment passed the FIBI BIC 1/3 times and passed the BMIBI BIC 0/1 times in the past 10 years. Also, 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).
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 between 2008 and 2012 to be considered “monitored”. This segment had multiple samples collected in the previous 10 years (2003-2012); however, the samples were not collected during 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).
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.
A fish kill occurred in this stream segment on August 27, 2001. Approximately 2,500 fish, mostly minnows, shiners, and creek chubs were killed along about 500 yards of Bear Creek. The value of these fish was estimated to be $219.93. The source of the kill was traced to a hog confinement facility. The party responsible for the kill was identified, and restitution was sought. According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill during an assessment period indicates "partial support" of the aquatic life uses. If, however, a consent order has been issued to the party responsible for the kill and monetary restitution has been sought for the fish killed, the affected waterbody should be placed in IR Category 4d (impaired but TMDL not required). IDNR considers IR 4d fish kill waters with no subsequent kills reported in at least five years subsequent to the kill as appropriate for movement from IR Category 4d to either categories 2b or 3b (i.e., Iowa’s list of waters in need of further investigation). Thus, this assessment segment remained in Category 3b of Iowa’s 2010 and 2010 Integrated Reports. IDNR considers IR Category 4d waterbodies where no additional kills have been reported for this stream for over 10 years, as appropriate for IR Category 3a (not assessed). Thus, this assessment is moved to IR Category 3a for the current (2014) cycle.
