Assessment Comments
Assessment remains based on 1998 IDNR/SHL biological sampling data: FIBI scores = 20, 24 (both poor) and 32, 37 (both fair). FIBI BIC = 33.
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 (2014) 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 are assessed (evaluated) as "partially supported" (IR 5b-t) based on results of IDNR/SHL biological (biocriteria) sampling in 1998. The biological monitoring data are now greater than 10 years old. As water quality data age, they become less able to represent current water quality conditions. According to IDNR’s assessment/listing methodology, waterbodies with assessments based on data older than ten years will be considered “not assessed” unless the previous assessment indicated impairment of the assessed use. Because the presumptive Class B(WW1) aquatic life uses of this assessment segment have been assessed as Section 303(d)-impaired (IR Category 5), the impairment of the presumptive aquatic life uses will remain in IR Category 5b-t. Note: All of the FIBI scores increased compared to what was reported in previous Section 305(b) reports but the segments is still not meeting Biological Impairment Criteria. Prior to the 2008 Section 305(b) assessment cycle, the FIBI scores were calculated using erroneous data.
EXPLANATION: The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “partially supported” based on data collected in 1998 as part of the IDNR/SHL stream biological sampling project. The 1998 FIBI scores were 20, 24 (both poor) and 32, 37 (both fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 33. This segment passed the FIBI BIC 0/4 times in the last 15 years. Even though this site failed to meet the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.
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 15 years (1998-2012); however, the samples were not collected during a five-year period and were not collected in multiple years. 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, 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).
Also, the data from the 1998 biological sampling are now older than 10 years old and are thus of questionable utility for assessing current water quality and biological conditions. Because, however, this segment is a 303(d) listed water, the impairment will remain until monitoring is conducted to show “full support” of the aquatic life uses.
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.
