Assessment Comments

Assessment based on results of IDNR ambient monitoring in 2000 and 2001. Assessment based on 2000 biocriteria data: Fish IBI= 28 (fair), BM-IBI= 54 (fair).

Basis for Assessment

[NOTE:  For the 2002 report, the previous waterbody segment for Old Mans Creek (IA 02-IOW-0150-0), which extended 40 miles from the its mouth to its confluence with Hog Run in Iowa County, was split into four subsegments:  (1) mouth to unnamed tributary southwest of Iowa city (IA 02-IOW-0150-1), (2) unnamed tributary southwest of Iowa City to unnamed tributary southwest of Cosgrove (IA 02-IOW-0150-2), (3) unnamed tributary southwest of Cosgrove to Convey Creek (IA 02-IOW-0150-3), and (4) Convey Creek to Hog Run, Iowa Co.  (IA 02-IOW-0150-4).   The assessments devleoped for previous Section 305(b) repoting cycles (found in the assessment in formation for segment IA 02-IOW-0150-2) apply to the original 40-mile segment.]

SUMMARY:  The Class B(LR) aquatic life uses remain assessed as "fully supported / threatened."  Fish consumption uses are not assessed.   The assessment of support of the Class B(LR) uses is based on results of monitoring conducted on Old Mans Creek near Iowa City at the Co.Rd.  W62 bridge from October 2000 to September 2001 as part of the IDNR ambient water quality monitoring program.   EXPLANATION:  Results of the IDNR monitoring showed no violations of Class B(LR) water quality criteria in the 12 samples analyzed for pH, dissolved oxygen, and ammonia.   In addition, no violations of Class B(LR) chronic criteria occurred in the 4 samples analyzed for pesticides.   Although the monitoring results for conventional and toxic parameters suggests "full support" of the aquatic life uses, the assessment of "fully supported / threatened" is used due to concerns with results of past biological monitoring (see assessment for the 2000 report).   Additional biological monitoring is needed to better determine the status of the aquatic communities of this stream.   Fish consumption uses are "not assessed because (1) data used for the previous assessment (see 1998 assessment above) are now considered too old (greater than five years) for characterizing current water quality conditions and (2) fish consumption uses are not considered appropriate for Class B(LR) streams.  

The assessment was based on data collected in 2000 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 2000 Fish IBI score was 28 (fair) and the BM-IBI score was 54 (fair).  The aquatic life use support was assessed as fully supported / threatened (=FST), 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.