Assessment Comments
Assessment is based on results of (1) 2001 Biocriteria sampling upstream from the Milford WWTP: Fish IBI= 38(fair),50(fair); BM-IBI= 14(poor),44(fair) & (2) IDNR/UHL TMDL monitoring in 2001. See attached document for details.
Basis for Assessment
[NOTE: Waterbody IA 06-LSR-0305_0 is a new segment for 2002 report that encompasses the general use-only reach of Milford Creek (unnamed tributary in S18, T98N, R36W, Dickinson Co. to outlet of Lower Gar Lake). See waterbody IA 06-LSR-0300_0 for previous Section 305(b) assessments that were applied to both the (lower) Class B(LR) reach and the (upper) general use-only reach of Milford Creek.]
SUMMARY: The general aquatic life uses were assessed as "partially supported." The sources of data for this assessment include results of (1) biological monitoring conducted in September 2001 and (2) monthly monitoring conducted by IDNR and UHL upstream from the Milford wastewater treatment plant at one location (station 11300001) from April to November 2001 as part of monitoring in support of TMDL development. Although this segment of Milford Creek is classified only for general uses in the Iowa Water Quality Standards, results of water quality monitoring were compared to Class B(LR) aquatic life criteria for purposes of estimating potential water quality impacts. EXPLANATION: Data upon with previous assessments were based (see assessment for the 1998 report for waterbody IA 06-LSR-0300_0) were collected in 1994 and 1995 and are now considered too old (greater than five years) for characterizing current water quality conditions. The current assessment was based on data collected in 2001 as part of the DNR/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 2000 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-1998. Despite the results of biological monitoring that show impairment, results of chemical monitoring in this stream segment show relatively good water quality. None of 8 samples collected from April through November violated Class B(LR) water quality criteria for dissolved oxygen (minimum value = 5.2 mg/l), pH (range of 7.6 to 8.7 units), or ammonia-nitrogen (maximum value = 0.60 mg/l). 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 general aquatic life uses as "partially supported."
