Assessment Comments

Assessment remains based on: (1) IDNR/SHL monthly monitoring conducted from March to November 2001, near the mouth of Buffalo Creek at Anamosa (Site 11; STORET station 11530001) in support of TMDL development for this stream reach, (2) results of sampling at four sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), (3) results of Iowa DNR freshwater mussel surveys at three sites in 2012, and (4) IDNR/SHL biological sampling in August 2001 conducted as part of the stream biocriteria 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, and due to the completion of a Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life uses (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 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 (2012) mussel surveys.   Due to the age of other data available to assess support of the Class B(WW1) aquatic life uses (> 10 years), these uses are considered "not assessed" (IR 3a) for the current IR cycle.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this stream reach.   The sources of data for this assessment are the results of sampling at four sites for the 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al.   2000) and (2) results of Iowa DNR freshwater mussel surveys at three sites in 2012.  

EXPLANATION:  The Class A1 uses remain “not assessed” due to the lack of water quality information upon which to base an assessment.  

Results of IDNR surveys of freshwater mussels at three sites in this assessment segment in 2012 suggest that, based on IDNR's assessment methodology, the 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 2012:

                                                          1984             1998            2012
No.  of live mussel species:                 11                 4                 7


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 (64%) 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 2012, 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 (36%).  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).

Other data upon which the assessment of the Class B(WW1) aquatic life uses have been based (i.e., Iowa DNR TMDL-related chemical/physical water quality monitoring in 2001 and Iowa DNR/SHL biological (fish & macroinvertebrate) monitoring in 2001) have now aged beyond 10 years.   Because these data are now more than ten years old, the Class B(WW1) uses are not considered “not assessed.”  That is, as water quality data age, they are less able to represent current water quality conditions.   As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect.   Additional monitoring is needed in this assessment segment to update status of its aquatic communities and chemical/physical water quality.

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