Assessment Comments
Assessment remains based on (2) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), (2) results of Iowa DNR freshwater mussel surveys in 2008 and 2013, and (3) 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" (IR 3a) due to the lack of information upon which to base an assessment. The previous impairment of Class B(WW1) aquatic life uses due to declines in the freshwater mussel community of this segment is de-listed based on results of new (2013) mussel surveys. Based on results of Section 319 monitoring in this segment in 2008, the Class B(WW1) aquatic life use are assessed as "fully supporting" (IR 2a). Fish consumption uses remain "not assessed" (IR 3a). Sources of data for this assessment include (1) results of the report “Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams, (2) results of Iowa DNR freshwater mussel surveys in 2008 and 2013, and (3) 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: The presumptive Class A1 (primary contact recreation) uses are remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supporting" based on results of Section 319 monitoring in 2008 at Buffalo Creek sites 5 and 7. 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, thus suggesting good chemical water quality in this assessment segment.
Results of IDNR surveys of freshwater mussels at three sites in this assessment segment in 2013 suggest that, based on IDNR's assessment methodology, the previous biological impairment based on the apparent decline of freshwater mussels no longer exists. The following is a summary of these surveys:
--Total number of live freshwater mussel species in this segment from surveys conducted in 1984 (Frest (1987), in 1998 (Arbuckle et al. 2000), and IDNR Watershed Improvement Section staff (J. Kurth) in 2008 and 2013:
1984 1998 2008 2013
No. of live mussel species: 13 0 0 9
The original impairment was based on a comparison of sampling results from 1998 and 1999 (Arbuckle et al. 2000) to results from stream sites surveyed in 1984 and 1985 by Frest (1987). Impairment 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. According to the IDNR assessment methodology, greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggested an impairment of the aquatic life uses. The degree of decline in the number of freshwater mussel species in this segment between 1984 and 1998 (100%) suggested “partial support” (impairment) of the Class B(WW) aquatic life uses for purposes of Section 303(d) listing. Results of the IDNR's surveys in 2013, however, show recovery in the number of freshwater mussel species in this assessment segment, with less than a 50% difference in the current (2013) versus historical (1984) mussel species richness (31%). Due to the lack of a protocol for identifying biological thresholds that indicate "full support" of a freshwater mussel community, this impairment is moved from Category 5b of Iowa's Integrated Report to IR Category 3a (insufficient information to develop an assessment of support of uses).
The fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
