Wapsipinicon River IA 01-WPS-347

Assessment Comments

Assessment is based on: (1) the results of monitoring conducted by USGS on Wapsipinicon River near Tripoli from March 2010 to September 2012 as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05420680) and (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998-99.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses.   Due to changes in Iowa’s surface water classification that were approved by U.S.  EPA in February 2008, and due to the completion of a Use Attainability Analysis in 2007, this segment is now designated for Class A1 (primary contact recreation) uses.   The stream remains designated for aquatic life uses (now termed Class B(WW1) aquatic life uses).   Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]

SUMMARY:  The Class A1 (primary contact recreation uses) remain “not assessed” (IR 3a) due to lack of data for indicator bacteria upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (monitored) as "fully supported" (IR 2a) based on results of ambient physical/chemical monitoring in 2010 through 2012.   The fish consumption uses remain “not assessed” (IR 3a) due to the lack of recent fish contaminant monitoring in this assessment segment.   The sources of information for this assessment include (1) the results of monitoring conducted by USGS on Wapsipinicon River near Tripoli from March 2010 through September 2012 as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05420680) and (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998-99.   Note:  this is the same assessment as that developed for the next downstream waterbody:  IA 01-WPS-0020-7.  

EXPLANATION:  The Class A1 (primary contact recreation uses) remain “not assessed” due to lack of data for indicator bacteria upon which to base an assessment.   No samples were analyzed for indicator bacteria at USGS station 05420680 during the 2010-12 period.

The results of USGS NAWQA monitoring from 2010 through 2012 suggest "full support" of the Class B(WW1) aquatic life uses.   No violations of state water quality criteria occurred in the approximately 25 samples analyzed for dissolved oxygen, pH, and ammonia or in the 23 samples analyzed for the pesticides chlorpyrifos and dieldrin.  

Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams also suggest “full support” of the aquatic life uses of this stream segment.   As part of this study, sampling results from 1998 and 1999 (Arbuckle et al.   2000) were compared to results from stream sites surveyed in 1984 and 1985 by Frest (1987).   On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa’s streams and rivers from the mid-1980s to the late 1990s.   Results of this comparison were used by staff of the Iowa DNR to assess the degree to which the aquatic life uses of the sampled stream segments are supported.   For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey.   Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggests an impairment of the aquatic life uses.   Species richness of freshwater mussels at the three sample sites in this stream segment were 8, 6, and 4 in the 1984-85 period and were 6, 6, and 4, respectively, in the 1998-99 period.   The species richness between the 1984-85 and 1998-99 periods is similar at these sites, with an average decline of only minus 8%.   Thus, based on IDNR's assessment approach, these results do not suggest impairment of the aquatic life uses.   This is one of the few river/stream segments sampled by Arbuckle et al.   (2000) that did not show significant declines in species richness between the 1984-85 period and the 1998-99 period.   As presented by Arbuckle et al.   (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high in-stream levels of nutrients (phosphorus and nitrogen).   Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness.  

Fish consumption uses are not assessed due to the lack of recent fish contaminant monitoring in this river segment.   Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.   These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.