Buffalo Creek IA 01-WPS-374

The Class B(WW1) uses are assessed (monitored) as "fully supporting" based on results of DNR/SHL biological monitoring of fish and aquatic macroinvertebrates in 2012 and 2016. 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 2016 FIBI score was 77 (excellent) and the BMIBI score was 73 (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 riffle habitat FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70. This segment passed the FIBI and BMIBI BICs 2/2 times in the last five years (2012-2016).

This aquatic life assessment is now considered "monitored" based on a change in the 2010 DNR assessment methodology. DNR 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 and BMIBI samples in the previous five years (2012-2016).

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 DNR assessment/listing methodology, this percent decline does not indicate impairment of the Class B(WW1) aquatic life uses. Similarly, results of DNR 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 DNR 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.

Fish consumption uses are assessed as "fully supported" based on results of DNR fish tissue monitoring at Central City in 2016. The average level of mercury in the tissue plugs from three smallmouth bass in 2016 was 0.05 ppm (SD=0.0).The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The levels of contaminants in the tissue samples from fish collected at Central City do not exceed any of Iowa’s consumption advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.