Assessment Comments
Assessment based on results of IDNR/UHL biological (REMAP) monitoring in 2002.
Basis for Assessment
SUMMARY: The general aquatic life uses were assessed (evaluated) as “partially supported” based on results of IDNR/UHL biological monitoring conducted in 2002 as part of the REMAP project. Because assessing support of aquatic life uses in general use-only waters with biological assessment methods developed for Class B(LR) and Class B (WW) streams is problematic, the assessment type will be considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to “monitored” (indicating an assessment with relatively higher confidence.
EXPLANATION: The assessment was based on data collected in 2002 as part of the DNR/UHL stream REMAP project. 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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 Fish IBI score was 48 (fair) and the BM-IBI score was 47 (fair). The aquatic life use support was assessed as Partially Supporting (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
This assessment is considered “evaluated” (of lower confidence) due to the lack of a biological assessment protocol for general use-only streams. IDNR’s existing protocol has been calibrated to aquatic life reference conditions in wadeable Class B(LR) and Class B(WW) streams. The aquatic environment of most general use streams is one of extremes in water quality. Consequently, general use-only streams tend to have biological diversity that is low relative to more stable aquatic environments of Class B(LR) and Class B(WW) streams. Thus, the use of biological assessment methods developed for the ecologically more stable and diverse Class B(LR) streams to assess general use reaches will likely overstate the existence of impairment. For these reasons, general use-only stream reaches that show a failure to meet regional expectations for aquatic biota (fish or aquatic macroinvertebrates) of Class B(LR) streams, 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 waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation”.
As part of the REMAP project, diurnal dissolved oxygen/temperature monitoring conducted during July-August 2002 found substantial fluctuation of d.o. levels, including nighttime sags (<3 mg/L), associated with very high estimated levels of community respiration and primary production. Levels of BMIBI metrics that are sensitive to organic enrichment suggest a nutrient enrichment/algal growth-related water quality problem. Habitat modification that has resulted in a wide and shallow stream channel with high solar input may contribute to algal growth. Additional sampling data are needed to evaluate the extent, causes and sources of this water quality problem.
