Assessment Comments
Assessment based on 2003 REMAP d.o./temp. diurnal monitoring, 2003 REMAP biological sampling, and 2006 IDNR Fisheries Bureau sampling: FIBI = 27 (fair), 31 (fair), BMIBI = 35 (fair). FIBI average = 29. Non-riffle habitat FIBI BIC = 32; BMIBI BIC = 62.
Basis for Assessment
[Note: Prior to the current (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 (2008) 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/EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment. The evaluated "not supporting" biological assessment of the presumptive Class B(WW1) aquatic life uses was based on data collected in 2003 as part of the DNR/UHL stream REMAP project and data from a 2006 IDNR Fisheries Bureau sampling project. In July 2003, a dissolved oxygen and temperature continuous monitoring instrument was deployed in the stream for 13 days. The data logger recorded an early morning dissolved oxygen level below 2 mg/L, which is substantially less than the instantaneous criterion of 4 mg/L for Class B(WW1) streams. This evidence of presumptive Class B(WW1) impairment is considered "evaluated" rather than "monitored" because the data were obtained from a single, short-term monitoring event.
Additionally, a series of biological metrics that 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 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 2003 REMAP FIBI score was 27 (fair) and the 2003 REMAP BMIBI score was 35 (fair). The 2006 Fisheries FIBI was 31 (fair). The FIBI average was 29. 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 1994-2004. The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62. The average FIBI score and the BMIBI score fail to meet the BIC.
This assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for headwater streams. 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. For these reasons, headwater stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) will not be added to Iowa’s Section 303(d) list of impaired waters (Category 5 of the Integrated Report). The assessment type for these assessed waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence).
