Buffalo Creek IA 01-WPS-374

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

The Class B(WW1) uses are assessed (evaluated) as "fully supporting" based on results of IDNR/SHL biological monitoring of fish and aquatic macroinvertebrates in 2001, 2008 and 2012.  This assessment is based on data collected in 2001, 2008 and 2012 as part of the IDNR/SHL stream biocriteria project.  A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.  The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach.  The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).  The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2001 BMIBI scores were 71 and 58 (both good).  The 2008 FIBI score was 77 (excellent) and the BMIBI score was 69 (good).  The 2012 FIBI score was 86 (excellent) and the BMIBI score was 87 (excellent).   The aquatic life use support was assessed (evaluated) as fully supported (=FS), based on a comparison of the FIBI and 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 1994-2008.  The non-riffle habitat FIBI BIC for this ecoregion is 44 and the natural/artificial substrate BMIBI BIC for this ecoregion is 70/52.  For one of the samples, artificial substrates were used and that BMIBI score (58) was compared to the artificial substrate BMIBI BIC (52).  For the three other samples, a Hess sampler was used and the BMIBI scores (87, 71 and 69) were compared to the natural substrate BMIBI BIC (70).  This segment passed the FIBI BIC 2/2 times in the last seven years (2008-2014) and passed the BMIBI BICs 3/4 times in the last 14 years (2001-2014). 

This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology.  IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between over a recent five-year period to be considered “monitored”.  This segment had multiple FIBI samples collected in the previous seven years (2008-2014) and multiple BMIBI samples collected in the previous 14 years (2001-2014).  Despite this change in assessment methodology and type, this aquatic life use assessment based on the biological (fish and macroinvertebrate) data remains "fully supporting". 

A re-examination of the results of surveys for freshwater mussels in this segment in 1984, 1998, and 2012 suggests that the original Section 303(d) listing for this segment was in error.  Although the percent decline in the freshwater mussel community between the 1984 and 1998 surveys was calculated as 51% (a marginal impairment based on Iowa's assessment methodology), the percent decline should have been calculated at only 25%.  That is, a total of 16 freshwater mussel species were found at the three 1984 sample sites.  A total of 12 species was found at these three sites during the 1998 surveys with a resultant percent decline of 25%.  According to the IDNR assessment/listing methodology, this percent decline does not indicate impairment of the Class B(WW1) aquatic life uses.  Similarly, results of IDNR surveys of freshwater mussels at these three sites in 2012 do not suggest impairment with a percent decline between the 1984 and 2012 survey periods of 38%.  Thus, the original listing of this segment of Buffalo Creek was in error.  The following is a summary of the surveys of freshwater mussels in this stream segment:

--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:        16       12       10


These results suggest that this segment of Buffalo Creek continues to support one of the more diverse communities of freshwater mussels in the state.

The fish consumption uses remain "not assessed" due to the lack of recent fish tissue monitoring in this stream reach.