Assessment Comments
Assessment remains based on results of IDNR/UHL biological REMAP sampling in 2006 and IDNR/UHL biological sampling in 1999.
Basis for Assessment
Note: Although USGS water quality monitoring was conducted at three locations in this segment during the 2004-2006 assessment period, only one sample per site was collected and analyzed. These 3 samples, collected on March 8, 2005, did not violate the respective Class B(WW2) criteria for ammonia, dissolved oxygen, or pH. This amount of data is insufficient for developing an updated assessment of support of designated uses.
SUMMARY: The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological REMAP sampling in 2006 and IDNR/UHL biological monitoring upstream and downstream of the Ankeny WWTP in 1999.
EXPLANATION: The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.
The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supporting” based on biological data collected in 2006 as part of the DNR/UHL stream REMAP project and IDNR/UHL biological monitoring upstream and downstream of the Ankeny WWTP in 1999. 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 1999 FIBI scores were 37, 37, 30 (fair) and 23 (poor). The 1999 BMIBI scores were 48, 54 (fair), 68, 74 (good). The 2006 FIBI score was 53 (good) and the BMIBI score was not calculated due to very low benthic macroinvertebrate colonization. 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 1994-2004. 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 3/5 times and passed the BMIBI BIC 2/4 times in the past 10 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 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous 10 years (1999-2008); however, the multiple samples were not collected during 2004-2008 and were not collected in multiple years (BMIBI). 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).
