Assessment Comments

Assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 2004: BMIBI = 71, 72 (both - good); (2) ISU statewide survey of freshwater mussels in 1998-99.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) 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), this segment is also now presumptively 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 presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW1) aquatic life uses are assessed (evaluated) as "not supported" based on results of the 1998-99 statewide assessment of freshwater mussels in Iowa streams by Arbuckle et al.  (2000).   However, results of IDNR/UHL biological (biocriteria) monitoring in 2004 suggest "full support" of these aquatic life uses based on sampling of the benthic macroinvertebrate community.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.  

EXPLANATION:  Results from the IDNR/UHL biocriteria sampling in 2004 suggest that the Class B(WW1) uses are "fully supported."  The 2004 BMIBI scores were 71, 70 (both good).   The aquatic life use support was assessed as fully supported (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The natural substrate BMIBI BIC for this ecoregion is 70.

Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams, however, suggest an impairment to the aquatic life uses of this stream segment.   [Note:  because the data from Arbuckle et al.  (2000) are now older than five years, the assessment category is changed from a “monitored” (i.e., a higher confidence assessment) to “evaluated” (i.e., lower confidence assessment).   Despite this change in assessment category, the impairment indicated by these data remains in IR Category 5 (i.e., Section 303(d) list) until more recent data suggest a good cause for de-listing.]  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).   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.   For stream segments having four or more species reported for the 1984-95 survey, 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.   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 one sample site in this segment of Lime Creek was 9 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%.   Based on these results, the aquatic life uses were assessed as “not supported.”  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 instream 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 remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.