North Cedar Creek IA 01-YEL-431

Assessment Comments

Assessment is based on results of water quality and biological monitoring conducted as part of the Sny Magill / Blood Run project.

Basis for Assessment

SUMMARY:  The Class B(CW) coldwater aquatic life remained assessed as "fully supported."  Fish consumption uses remain "not assessed."  EXPLANATION:   The assessment of the Class B(CW) aquatic life uses is based on results of monitoring of chemical water quality, habitat quality, fish populations, and aquatic macroinvertebrate populations at North Cedar Creek; this monitoring has been conducted since 1992 as part of the Sny Magill Creek Nonpoint Source Pollution Monitoring Project.   This monitoring shows good chemical water quality and aquatic life.   Results of weekly chemical water quality monitoring from October 1996 through September 1999 at the stations on the lower reach of this stream show (1) no violations of the Class B(CW) water quality criterion for dissolved oxygen (7.0 mg/l) in the 155 samples collected (minimum level = 8.0 mg/l) and (2) no (estimated) violations of the Class B(CW) chronic criterion for ammonia-nitrogen in 156 samples collected (violations of the temperature/pH-dependent water quality criteria for ammonia-nitrogen were based on "worst case" estimated values of pH; pH was not measured during sample collection at the Sny Magill project sites).   The episodes of low dissolved oxygen that occurred in the Sny Magill and Bloody Run watersheds from 1992-1994 (see assessments for the 1996 and 1998 reports above) were due, at least in part, to problems with field equipment and certain reagents used to measure dissolved oxygen.   Since July 1995, measurements have been made with a YSI portable dissolved oxygen meter.   During the period October 1996 through September 1999, none of the samples collected at monitoring sites in the Sny Magill Nonpoint Source project have violated the Class B(CW) water quality criterion for dissolved oxygen of 7.0 mg/l.   Based on the Hilsenhoff Biotic Index, results of biological monitoring for benthic macroinvertebrates suggest good to very good water quality.   Fish consumption uses remain "not assessed" due to lack of recent fish tissue monitoring in this stream reach.   For more information on the Sny Magill Creek Nonpoint Source Pollution Monitoring Project visit the DNR-Geological Survey Bureau web site at http://www.igsb.uiowa.edu/inforsch/waterag.htm.