Assessment Comments
Assessment is based on 1997, 2003 and 2007 IDNR/UHL biological monitoring data: 2003 FIBI scores: 26 (fair), 21 (poor) and 2007 FIBI score was 36 (fair); 1997 BMIBI scores: 43 (fair) and 59 (good), 2003 BMIBI score was 38 (fair) and results of a fish kill investigation in 2001. 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 (2010) 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" 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" based on the results of IDNR/UHL biological (biocriteria) monitoring in 1997, 2003 and 2007 and results of a fish kill investigation in 2001.
EXPLANATION: This evaluated biological assessment was based on data collected in 1997, 2003 and 2007 as part of the IDNR/UHL 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 1997 BMIBI scores were 43 (fair) and 59 (good) and 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 1994-2004. 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 in the last six years and passed the BMIBI BIC 0/3 times in the past 14 years.
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 2006 and 2010 to be considered “monitored”. This segment had multiple samples collected in the previous 14 years (1997-2010); however, the samples were not collected during 2006-2010. 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.
In addition to the results of biological monitoring, a fish kill that occurred on August 27, 2001, also suggests that the aquatic life uses be assessed (evaluated) as "partially supported." 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 year 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 remains in Category 3b of Iowa’s 2010 Integrated Report.
