Assessment Comments
Assessment is based on results of (1) IDNR investigation of a fish kill in September 2001; (2) IDNRU/UHL biological (REMAP) sampling in 2002 (Fish IBI= 5 (poor), BM-IBI= 30 (poor)); and (3) IDNR/UHL biological (biocriteria) sampling in 1999 (Fish IBI= 33 (fair), BM-IBI= 48 (fair)).
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as “not supporting” based on results of IDNR/UHL biological monitoring for fish and aquatic macroinvertebrates conducted in 2002. “Non-support” of the Class B(LR) uses is also indicated by the occurrence of pollutant-caused fish kills in 2001 and 2002. The sources of data for this assessment include (1) results of biological monitoring conducted in 2002 as part of the DNR/UHL REMAP project, (2) results of IDNR investigations of fish kills in 2001 and 2002 as retrieved from the IDNR fish kill data base, and (3) results of biological monitoring conducted in 1999 by IDNR/UHL as part of the stream biocriteria project.
EXPLANATION: This assessment was based, in part, on biological data collected in 2002 as part of the DNR/UHL REMAP project. The 2002 Fish IBI score was 5 (poor) and the BM-IBI score was 30 (poor). Thus, 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.
In addition to the indication of poor biotic integrity indicated by results of IDNR/UHL REMAP monitoring, this stream segment has a history of fish kills, the most recent occurring on September 19, 2001 and—almost to the day—one year later on September 18, 2002 (an additional kill occurred in 1996; see the assessments developed for the 1996 and 1998 reporting cycles for more information). The September 2001 kill occurred south of Royal and was caused by the discharge of cattle manure from an open feedlot; an estimated 8,900 fish were killed. No estimate of the length of stream affected is available. Water quality monitoring conducted with a field kit during the fish kill investigation showed a dissolved oxygen concentration of zero and an ammonia-nitrogen concentration of 12.5 mg/l. The September 2002 kill was caused by the discharge of cattle manure from the same feedlot that caused the September 2001 kill. An estimated 9,000 fish were killed over a 4.3 mile segment of stream. The same party was responsible for both kills; IDNR sought restitution for both kills. According to DNR's assessment methodology for Section 305(b) reporting, occurrence of more than one pollution-caused fish kill during the most recent three-year period (2000-02) indicates severe water quality impacts and "non-support" of the aquatic life uses.
The current (2004) assessment reflects a declining trend in the biotic condition of this stream segment. A biological assessment was conducted on Willow Creek in 1999, prior to the fish kill in 2001, as part of the IDNR/UHL stream biocriteria project. Similar to current procedures, a series of biological metrics which reflect stream water quality and habitat integrity were calculated from the sampling data on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The 1999 Fish IBI score was 33 (fair) and the BM-IBI score was 48 (fair). These results suggested that the aquatic life uses were "fully supported / threatened." The fish and macroinvertebrate scores in 1999 (33 and 48, respectively) are much higher than the respective scores for fish and macroinvertebrates in the 2002 sampling (5 and 30, respectively). Based on this comparison, and based on the fish kill history of this stream, a connection likely exists between the pollution-caused fish kills and the decline in biotic integrity.
