Assessment Comments
Assessment remains based on (2) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000) and (2) results of monitoring at two sites (Buffalo Creek 5 and Buffalo Creek 7) conducted in 2008 as part of a Clean Water Act Section 319 water quality project.
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, including fish consumption uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, 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 remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW1) aquatic life use uses remain assessed (evaluated) as "not supported" based on information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000). 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 streams and rivers from the mid-1980s to the late 1990s. This stream segment remains in Category 5b of Iowa's Integrated Report. Fish consumption uses remain "not assessed." Sources of data for this assessment include (1) results of the report “Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams and (2) results of monitoring at two sites (Buffalo Creek 5 (STORET station 15100005) and Buffalo Creek 7 (STORET station 15280010))conducted as part of a Clean Water Act Section 319 water quality project from June through December 2008.
EXPLANATION: 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 TMDL & Water Quality Assessment Section 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 three sample sites in this segment of Buffalo Creek was 2, 12, and 3, respectively, in the 1984-85 period (average of approximately 6 species) and was zero at all three sites in the 1998-99 period for a percent change of minus 100%. Based on these results, the aquatic life uses are assessed (monitored) 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. 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 type, this waterbody remains in IR Category 5b.
Results of Section 319 monitoring in 2008 at Buffalo Creek sites 5 and 7 suggest good chemical water quality in this assessment segment. None of the 21 samples collected at each monitoring station in 2008 exceeded Class B(WW1) water quality criteria for ammonia, dissolved oxygen, pH, and temperature.
The fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
