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 May 2006 through August 2008 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 and 2008 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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 (2010) 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 and 2008 and based on results of chemical/physical water quality monitoring from 2006 to 2008. 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 May 2006 through August 2008 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 and 2008 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 mean of E. coli in the 20 samples collected at station 15660007 during the recreational seasons of 2006 through 2008 was 165 orgs/100 ml. This geometric mean slightly exceeds the Class A1 criterion of 126 orgs/100 ml. Six of the 20 samples (30%) exceeded Iowa’s 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 the geometric mean of E. coli is greater than the applicable state criterion, the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Despite the impairment of the presumptive Class A1 uses, the levels of indicator bacteria in this stream appear to be very low relative to levels seen in most monitored streams and rivers in the state.
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 23 samples collected during the 2006-2008 period as part of Cedar River/Mitchell County monitoring violated Class B(WW2) criteria for dissolved oxygen (minimum = 5.9 mg/l), ammonia, or pH. The maximum temperature in the 23 samples collected over the three-year period was 24.4C (76F) on July 10, 2007. Levels of ammonia were extremely low in this stream during the 2006-08 period with 21 of the 22 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. None of the 24 samples collected during this period had a water temperature of greater than 20C (water samples were collected from late morning to early afternoon). Taken together, these monitoring results suggest excellent water quality in this stream.
The assessment was based on data collected in 2001 and 2008 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 90 (excellent). 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 and BMIBI BICs 2/2 times in the last eight years.
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 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous eight years (2001-2008); however, the multiple samples were not collected during 2004-2008. Despite this change in assessment methodology and type, this assessment remains "fully supporting".
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.
