Assessment Comments

Assessment is based on (1) IDNR/UHL ambient monitoring in 2004; (2) a 2002 summary of trout reproduction prepared by the IDNR Fisheries Bureau and (3) 2003 IDNR biocriteria sampling data: 7/8 coldwater biological indicators met the criteria - Fully Supporting (FS).

Basis for Assessment

SUMMARY:  The Class B(CW) aquatic life uses are assessed (monitored) as "fully supported" based on results of both biological and chemical/physical monitoring.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.   Sources of data for this assessment include (1) results of IDNR/UHL chemical/physical water quality monitoring conducted from May to December 2004 at STORET station 15030004; (2) information from the April 2002 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau and (3) 2003 UHL special project sampling.  

EXPLANATION:  The results of the IDNR/UHL water quality monitoring in 2004 show three violations of the Class B(CW) criteria for dissolved oxygen (7.0 mg/l) in the 26 samples (12%) collected.   The violations were relatively minor (lowest DO level = 5.4 mg/l).   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), "partial support" of aquatic life uses is indicated if criteria are exceeded in from 11 to 25% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen).   Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(CW) uses of Dousman Creek.  

According to the 2002 summary of trout reproduction in Iowa streams, this reach of Dousman Creek is in the category of Iowa trout streams that exhibit recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population for the target trout species at this time.  

The assessment of the Class B(CW) aquatic life uses was based on data collected in 2003 as part of the UHL stream sampling special project.   A series of eight (8) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the biocriteria sampling data and supplemental IDNR Fisheries Bureau data.   The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.   Sites that score 5-8 are Fully Supporting (FS), sites that score 2-4 are Partially Supporting (PS), and sites that score 0-1 are Not Supporting (NS).   The 2003 coldwater biological indicator score was 7/8.   The aquatic life use support was assessed (monitored) as fully supporting (= FS), based on a comparison of the coldwater biological indicator score with biological assessment criteria established for this Section 305(b) report.   The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2004 and with assistance from the IDNR Fisheries Bureau.

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.