Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) sampling in 2001 (Fish IBI= 38(fair), 50(fair); BM-IBI= 14(poor), 44(fair)) and (2) IDNR/UHL water quality monitoring in 2001 in support of TMDL development.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses were assessed (monitored) as "partially supported" based on results of biological monitoring in 2001. The sources of data for this assessment include results of (1) biological monitoring conducted in September 2001 and (2) monthly monitoring conducted by IDNR/UHL at one location (STORET station 11300002) from March to November 2001 as part of monitoring in support of TMDL development. Both the chemical and biological monitoring were conducted in the lower reach of Milford Creek approximately 1 mile SW of Milford.
EXPLANATION: The current assessment was based on data collected in 2001 as part of the IDNR/UHL stream biocriteria 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 F-IBI scores were 38 (fair) and 50 (fair); the BM-IBI scores were 14 (poor) and 44 (fair). The aquatic life use support was assessed as partially supported (=PS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
Despite the results of biological monitoring that show impairment, results of chemical monitoring in this stream segment show relatively good water quality. None of 9 samples collected from March through November 2001 violated Class B(LR) water quality criteria for dissolved oxygen (minimum value = 5.7 mg/l), pH (range of 7.9 to 8.9 units), or ammonia-nitrogen (maximum value = 0.40 mg/l). This monitoring, however, showed some extremely high levels of total phosphorus in this segment of Milford Creek. The mean, median, and maximum total phosphorus levels for the TMDL monitoring at the lower Milford Creek station in 2001 were 1.0, 0.7, and 2.2 mg/l, respectively. Sample values for total phosphorus in the September, October, and November samples were 2.2, 2.1, and 1.1 mg/l, respectively. These summary statistics suggest atypically high levels of total phosphorus in lower Milford Creek and potential problems with organic enrichment. Because biological monitoring is better able to reflect cumulative impacts of water quality over time and thus more accurately represents water quality conditions, the results of biological monitoring in 2001 were use to assess support of the Class B(LR) aquatic life uses of lower Milford Creek as "partially supported."
