Assessment Comments

Assessment is based on: (1) results of IDNR/UHL chemical/physical monitoring conducted from 2004-06 at STORET station 15030004 monitored as part of the Yellow River Watershed Project (YRWP); (2) results of IDNR bacterial 2006-08 at STORET station 15030004, (3) information from the May 2006 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau, and (4) 2003 UHL special project sampling.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.   EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]

SUMMARY:  The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported” due to levels of indicator bacteria that exceed state water quality criteria.   The Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.”  The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as "partially supported" based on results of chemical/physical monitoring for dissolved oxygen.   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 bacterial monitoring conducted from February 2006 to September 2008 at STORET station 15030004 monitored as part of the Yellow River Watershed Project (YRWP); (2) results of IDNR/UHL chemical/physical monitoring at station 15030004 from May 2004 through November 2006, (3) information from the May 2006 summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau and (4) 2003 UHL special project biological sampling.  

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria.   The Class A2 (secondary contact recreation) uses are assessed (monitored) as “fully supported.”  The geometric mean of E.   coli in the 34 samples collected at YRWP site 15030004 during the recreational seasons of 2006 through 2008 was 231 orgs/100 ml.   This geometric mean exceeds the Class A1 criterion of 126 orgs/100 ml.   Fifteen of the 34 samples (44%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.   EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if the geometric mean of E.   coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).  

The geometric mean of the 38 samples collected at this station during calendar years of 2006 through 2008 was 180 orgs/100 ml; this geometric mean is well below the Class A2 criterion of 630 orgs/100 ml.   Only one of the 38 samples (3%) exceeded Iowa’s Class A2 single-sample maximum criterion (2,880 orgs/100 ml.).   According to U.S.   EPA guidelines for Section 305(b) reporting, if the geometric mean is less than the applicable state criterion, and if less than 10% of samples exceed the single-sample maximum criterion, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S.   EPA 1997b).  

The Class B(CW1) coldwater aquatic life uses remain assessed (monitored) as “partially supported.”  The results of the IDNR/UHL water quality monitoring from May 2004 through November 2006 showed 20 violations of the Class B(CW1) criteria for dissolved oxygen (7.0 mg/l) in the 73 samples (27%) collected.   The violations were relatively minor (lowest DO level = 4.5 mg/l).   Similar to results for other sites monitored as part of the Yellow River Watershed Project, 2005 was a year of low dissolved oxygen:  16 of the 20 violations occurred from April through November 2005.   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, these results indicate that significantly more than 10 percent of the samples exceed Iowa’s Class B(CW1) dissolved oxygen criteria and thus suggest an impairment of the Class B(CW1) uses of Dousman Creek.   Note:  although IDNR station 15030004 was monitored for E.  coli through September 2008, monitoring for dissolved oxygen was not conducted after November 2006.   Improved levels of dissolved oxygen at other stations in the Yellow River basin after 2005 (e.g., station 15960002 on the Yellow River [IA 01-YEL-0080_3]) suggest the potential for improved water quality in Dousman Creek as well.

According to the May 2006 summary of trout reproduction in Iowa streams, this reach of Dousman Creek is in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species (brown trout) without any stocking.   This updated summary of trout reproduction suggests an improvement over the previous (April 2002) characterization for this stream (i.e., 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(CW1) aquatic life uses was also 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 6/8.   The aquatic life use support was assessed (evaluated) 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 1994-2008 and with assistance from the IDNR Fisheries Bureau.  

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.   IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”.   This segment had a single sample collected in 2003.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).    Despite this change in assessment methodology and type, this waterbody remains in IR Category 5a based on the other impairments.

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