Deer Creek IA 02-CED-591

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to violations of Iowa’s water quality criteria for indicator bacteria.  The geometric means of indicator bacteria (E. coli) in the 20 samples collected during the recreational seasons of 2012 and 2013 at CR-MC site 15660007 were as follows:  the 2012 geometric mean was 83 orgs/100 ml, and the 2013 geometric mean was 150 orgs/100 ml.  Only the 2013 geometric mean very slightly exceeded the Class A1 criterion of 126 orgs/100 ml; the 2012 geometric mean was well below the Class A1 criterion.  Three of the 20 samples (15%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  Please note, however, that relative to other Iowa streams, levels of indicator bacteria in this segment of Deer Creek continue to be very low. 

Both chemical/physical and biological data suggest that the Class B(WW-2) aquatic life uses should be assessed (monitored) as “fully supported.”  None of the 15 samples collected in 2012 and 2013 at station 15660007 violated Class B(WW2) criteria for ammonia or dissolved oxygen, and none of the eight samples analyzed for chloride exceeded their respective Class B(WW2) criteria.  One of the 15 samples (7%), however, did violate Class B(WW2) criteria for pH and for temperature.  Similar to the results of monitoring at other Mitchell County water quality stations on June 19, 2012, the water temperature was very high (34.6C) and violated the Class B(WW2) criterion.  The pH of the sample collected on May 22, 2012 was 9.2 units which exceeded the Class B(WW2) criterion of 9.0 units.  These monitoring results do not suggest impairment of the Class B(WW2) aquatic life uses.  According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as dissolved oxygen or temperature, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b).  According to IDNR’s assessment/listing methodology, however, the results from station 15660007 do not indicate that significantly greater than 10% of the samples exceed the Class B(WW2) criteria for dissolved oxygen, pH, or temperature.  Thus, the results of chemical/physical water quality monitoring in 2012 and 2013 in this segment suggest that the Class B(WW2) aquatic life uses should be assessed (monitored) as “fully supported.” 

The assessment of the Class B(WW2) aquatic life uses was also based on biological data collected in 2008, 2010 and 2013 as part of the IDNR/SHL stream biocriteria project.  The 2008 FIBI score was 73 (excellent) and the BMIBI score was 91 (excellent).  The 2010 BMIBI score was 71 (good).  The 2013 FIBI score was 76 (excellent) and the BMIBI score was 60 (good).  The aquatic life use support was assessed (monitored) as fully supporting (=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 BIC 2/2 times and passed the BMIBI BIC 2/3 times in the last seven years.  This assessment is considered "monitored" because there were two or more (BMIBI) samples collected from this segment in multiple years in a recent five year period (2010-2014). 

This segment of Deer Creek was sampled as part of the 1998-99 statewide study of freshwater mussels in Iowa streams and rivers (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.  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 Water Quality Bureau to assess the degree to which the aquatic life uses of the sampled stream segments are supported.  The results of this sampling on Deer Creek, however, showed an increase in species richness between the 1984-98 and 1998-99 survey periods.  Species richness of freshwater mussels at the one sample site in this segment was 7 in the 1984-85 period and was 12 in the 1998-99 period, respectively, for a percent change of plus 71%.  Relative to other sites in the 1998-99 ISU survey, the freshwater mussel community of Deer Creek is exceptional:  this stream tied with Buffalo Creek in Jones and Linn counties (IA 01-WPS-0110_2) for the highest mussel species richness (12) of the 118 survey sites used for purposes of Section 305(b) assessments, and this stream tied for the biggest increase in mussel species richness between the 1984 and 1998-99 survey periods (increase of 7 species).  These results suggest "full support" of the aquatic life uses.