Assessment Comments

Assessment is based on: (1) IDNR/UHL biological (REMAP) monitoring conducted in 2002-2004 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2006-2008 assessment period at the Highway 141-175 bridge at Mapleton (STORET station 10670002 (formerly station 911040)).

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) aquatic life uses, including fish consumption 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) and the results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) 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 violate state water quality criteria.   The Class B(WW1) aquatic life uses are assessed (evaluated) as "partially supported” based on results of biological monitoring in 2002, 2003, and 2004.   Results of ambient water quality monitoring from 2006 through 2008 suggest relatively good water quality in this river segment.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL biological (REMAP) monitoring conducted in 2002, 2003, and 2004 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2006-2008 assessment period at the Highway 141-175 bridge at Mapleton (STORET station 10670002 (formerly station 911040)).  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric mean level of indicator bacteria (E.  coli) in the 21 samples collected at the IDNR/UHL ambient monitoring station near Mapleton during summer recreational seasons of 2006-2008 (1,489 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Eighteen of the 21 samples (86%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

Regarding support of the Class B(WW1) aquatic life uses, results of ambient chemical/physical monitoring at the IDNR/UHL station at Mapleton showed no violations of Class B(WW1) water quality criteria during the 2006-2008 assessment period for dissolved oxygen (minimum value = 7.1 mg/l), ammonia nitrogen (maximum value = 1.6 mg/l) or pH (range = 7.6 to 8.6 units) in the 33 samples collected.   Levels of toxic metals in the two samples analyzed, were all below the analytical level of detection.   (Note: pesticides were not monitored at this site from 2006 through 2008.)  These results suggest “full support” of the Class B(WW1) aquatic life uses.

Despite results of ambient physical/chemical monitoring that suggest “full support” of aquatic life uses, results of biological monitoring suggest only “partial support” of these uses.   This assessment was based on biological data collected in 2002, 2003, and 2004 as part of the IDNR/UHL stream REMAP project.   A series of biological metrics that 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 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 2002 BMIBI score was 46 (fair).   The 2003 FIBI score was 9 (poor) and the 2003 BMIBI score was 55 (fair).   The 2004 FIBI score was 14 (fair) and the 2004 BMIBI score was 50 (fair).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The FIBI BIC for this ecoregion is 31 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI BIC 0/2 times in the last six years and passed the BMIBI BIC 1/3 times in the last seven years.   This assessment is considered “evaluated” because the drainage area (724 and 732 mi2) above the sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site failed the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.  

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 multiple samples collected in the previous 10 years (1999-2008); however, the samples were not collected during 2004-2008.   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  

Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river reach.