Assessment Comments

Assessment based on results of (1) IDNR/UHL ambient water quality monitoring from 2002-04 and (2) 2000 IDNR/UHL biological monitoring: FIBI = 27 (fair), BMIBI = 55 (fair). FIBI BIC = 36, BMIBI BIC = 51.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses are assessed (monitored) as "partially supported” based on results of chemical/physical monitoring and biological monitoring.   The assessment of support of the Class B(LR) uses is based on (1) results of IDNR/UHL monthly ambient water quality monitoring conducted on Old Mans Creek near Iowa City at the County Road W62 bridge (STORET station 10520001) from 2002 through 2004 and (2) results of biological monitoring conducted in 2000 as part of the IDNR/UHL stream biocriteria project.  

EXPLANATION:  Results of the IDNR/UHL ambient water quality monitoring from 2002 through 2004 showed no violations of Class B(LR) water quality criteria in the approximately 35 samples analyzed for dissolved oxygen, pH, and ammonia.   In addition, none of the approximately 10 samples analyzed for toxic metals and pesticides exceeded the respective Class B(LR) chronic criteria.   During the previous (2000-2002) assessment period, a single sample exceeded the Class B(WW) chronic criterion for the pesticide chlorpyrifos.   None of the 11 samples analyzed for this pesticide during the 2002-2004 period violated Class B(LR) criteria.  

Conversely, results of biological monitoring suggest that the Class B(LR) uses should be assessed as “partially supported”.  This assessment is based on biological 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 (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 score was 27 (fair) and the BMIBI score was 55 (fair).  The aquatic life use support was assessed as partially supported (= PS), 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 36 and the BMIBI BIC for this ecoregion is 51.