Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring in 2002 (Fish IBI= 18 (poor), BM-IBI= 33 (fair)) and (2) IDNR/UHL ambient water quality monitoring conducted from March-November 2002 in support of TMDL development.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as “not supported” based on results of biological monitoring for fish and aquatic macroinvertebrates conducted in 2002 as part of the DNR/UHL REMAP project. This assessment is also based on results of ambient chemical/physical water quality monitoring conducted by IDNR/UHL from March through November 2002 as part of TMDL monitoring (TMDL station 11; STORET station 11750003).
EXPLANATION: This assessment was based on data collected in 2002 as part of the DNR/UHL 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 18 (poor) and the BM-IBI score was 33 (fair). The aquatic life use support was assessed as Not Supporting (=NS), 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.
Habitat assessment and site photographs indicated channel incision, vertical eroding banks, narrow riparian buffer next to row crop land, and silt accumulations. Diurnal dissolved monitoring indicated levels lower than 3 mg/L can occur during summer months. Additional sampling data are needed to evaluate this potential water quality problem.
Despite results of biological monitoring that suggest “non-support” of the aquatic life uses, the results of chemical/physical water quality monitoring conducted in support of TMDL development suggest relatively good water quality in this stream. None of the 12 samples collected between March and November of 2002 had levels of dissolved oxygen, pH, or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides).
