Assessment Comments
Assessment remains based on 2006 IDNR/SHL stream REMAP d.o./temp. diurnal monitoring and biological sampling data: FIBI = 1 (poor); BMIBI = 20, 26 (both poor). FIBI BIC = 43, BMIBI BIC = 54.
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.gov/Portals/idnr/uploads/water/standards/files/swcdoc2.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.]
SUMMARY/EXPLANATION: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR Category 3a) due to the lack of information upon which to base an assessment.
The presumptive Class B(WW1) aquatic life uses remains assessed (evaluated) as “not supporting” (IR Category 5p) based on biological and water quality data collected in 2006 as part of the IDNR/SHL stream REMAP project. A dissolved oxygen and temperature continuous monitoring instrument was deployed in the stream for 9 days in July/August 2006. The data logger recorded an early morning dissolved oxygen level of 3 mg/L, which is substantially less than the instantaneous criterion of 4 mg/L for Class B(WW1) streams. Also, a precipitous drop in d.o. to near 0 mg/L was observed, which was accompanied by an elevated ammonia level of 6.1 mg/L on August 3, 2006. This water quality evidence of presumptive Class B(WW1) impairment is considered "evaluated" rather than "monitored" because the data were obtained from limited short-term sampling.
Additionally, 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 2006 FIBI score was 1 (poor) and the BMIBI scores were 20, 26 (both poor). The aquatic life use support was assessed (evaluated) as not supporting (=NS), 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 1994-2008. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 0/1 times and passed the BMIBI BIC 0/2 times in 2006. Even though this site failed both the FIBI and BMIBI BICs, 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; however, the samples were not collected in multiple years nor in the last five year period. 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.
