Assessment Comments
Assessment is based on results of (1) 2000 IDNR/UHL biological monitoring: FIBI = 2, 10 (poor), BMIBI = 58 (good), 45 (fair) and (2) IDNR/UHL ambient water quality monitoring conducted from 2002-2003 in support of TMDL development.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as “not supported” due to results of biological monitoring for fish and aquatic macroinvertebrates in 2000. The sources of data for this assessment include (1) results of IDNR/UHL biological monitoring conducted in 2000 as part of the stream biocriteria project and (2) results of IDNR/UHL ambient monitoring conducted near Chatsworth at Station 8 during the 2002-2004 assessment period in support of TMDL development (STORET station 11840003).
EXPLANATION: Results of biological monitoring conducted in 2000 as part of the DNR/UHL stream biocriteria project suggest impairment of the Class B(LR) aquatic life uses. 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 2000 FIBI scores were 2 (poor) and 10 (poor); the BMIBI scores were 58 (good) and 45 (fair). FIBI average was 6 and BMIBI average was 51.5. The aquatic life use support was assessed as not supporting (= NS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54.
In contrast, results of IDNR/UHL ambient water quality monitoring conducted from March 2002 through December 2003 in support of TMDL development suggest “full support” of the Class B(LR) aquatic life uses. Levels of ammonia-nitrogen, dissolved oxygen, and pH in the 23 samples analyzed were all below the respective Class B(LR) water quality criteria.
