Assessment Comments
Assessment remains based on results of (1) IDNR/UHL biological monitoring in 1996 and 2001: FIBI = 38 (fair) and 50 (fair); BMIBI = 41 (fair) and 58 (good) and (2) TMDL monitoring in 2001. FIBI BIC = 36, BMIBI BIC = 51.
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 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." Sources of information for this assessment include (1) results of biological monitoring conducted in 1996 and 2001 as part of the IDNR/UHL stream biocriteria project and (2) water quality monitoring conducted at one site in this segment from March to November 2001 by IDNR and UHL in support of TMDL development. The biological sampling data are now greater than five years old; therefore, this assessment is now considered "evaluated" instead of "monitored".
EXPLANATION: The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of biological monitoring conducted in 1996 and 2001. The biological assessment was based on data collected in 1996 and 2001 as part of the IDNR/UHL stream biocriteria project. The 1996 FIBI score was 38 (fair) and 41 (fair). The 2001 FIBI score was 50 (fair) and the BMIBI score was 58 (good). This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 1/2 times in the last 15 years. The aquatic life use support was assessed (evaluated) as partially supported (=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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.
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 (1996-2010); however, the samples were not collected during a five-year period. 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).
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.
Results of chemical/physical water quality monitoring conducted in 2001 in support of TMDL development show no violations of Class B(WW1) state water quality criteria for conventional parameters and ammonia-nitrogen in the nine monthly samples collected between March and November 2001 at the site 2 miles E of Tipton (Site 9) (the maximum value of ammonia-nitrogen was 0.12 mg/l). These results suggest "full support" of the aquatic life uses.
