Assessment Comments
Assessment is based on: (1) the results of ambient water quality monitoring conducted at station 15660007 on Deer Creek at Dancer Avenue from April 2008 through November 2010 as part of the Cedar River/Mitchell County study, (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999 and (3) results of 2001, 2008 and 2010 IDNR/UHL biological sampling near Carpenter.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008, this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 primary contact recreation uses are assessed (monitored) as “not supported” due to high levels of indicator bacteria. The Class B(WW2) aquatic life uses remain assessed (monitored) as “fully supported” based on results of IDNR/UHL biological monitoring in 2001, 2008 and 2010 and based on results of chemical/physical water quality monitoring from 2008 to 2010. Results from the 1998-99 statewide survey of freshwater mussels also suggest "full support" of aquatic life uses. The sources of data for this assessment are (1) the results of ambient water quality monitoring conducted at station 15660007 on Deer Creek at Dancer Avenue from April 2008 through November 2010 as part of the Cedar River/Mitchell County study, (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999 and (3) results of 2001, 2008 and 2010 IDNR/UHL biological sampling near Carpenter.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The geometric means of indicator bacteria (E. coli) in the 18 samples collected during the recreational seasons of 2008 through 2010 at CR-MC site 15660007 were as follows: the 2008 geometric mean was 200 orgs/100 ml, the 2009 geometric mean was 61 orgs/100 ml and the 2010 geometric mean was 102 orgs/100 ml. Only the 2008 geometric mean slightly exceeded the Class A1 criterion of 126 orgs/100 ml; geometric means for the 2009 and 2010 recreation seasons were well below the Class A1 criterion. Five of the 18 samples (28%) 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 are "not supported" (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 18 samples collected during the 2008-2010 period as part of Cedar River/Mitchell County monitoring violated Class B(WW2) criteria for dissolved oxygen (minimum = 6.0 mg/l) or pH. The maximum temperature in the 23 samples collected over the three-year period was 23.3 C. Levels of ammonia were extremely low in this stream during the 2008-10 period with five of the six samples analyzed having less than the detectable level of ammonia (< 0.05 mg/l); the only detectable level was 0.3 mg/l in the sample collected on April 1, 2008. Taken together, these monitoring results suggest excellent water quality in this stream.
The assessment was also based on data collected in 2001, 2008 and 2010 as part of the IDNR/UHL stream biocriteria project. The 2001 FIBI score was 68 (good) and the BMIBI score was 78 (excellent). The 2008 FIBI score was 73 (excellent) and the BMIBI score was 91 (excellent). The 2010 BMIBI score was 71 (good). The aquatic life use support was assessed (evaluated) 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 1994-2004. 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 3/3 times in the last 10 years.
This assessment is considered "monitored" because there were two or more (BMIBI) samples collected from this segment in multiple years from 2006-2010.
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.
