Assessment Comments
Assessment based on the February 2011 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.
Basis for Assessment
Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current (2014) assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.] This stream segment is identified as an Outstanding Iowa Water under the antidegradation policy in the Iowa Water Quality Standards.
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria. This is a new impairment for this assessment segment. The presumptive aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on the February 2012 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau and based on results of water quality monitoring in 2011. Although not designated for coldwater aquatic life uses in the Iowa Water Quality Standards/Surface Water Classification, this stream is considered a trout stream by the IDNR Fisheries Bureau and is identified as an "Outstanding Iowa Water" as part of Iowa's anti-degradation proram. Thus, this stream segment is assessed as a coldwater stream for the Iowa’s Integrated Reporting cycle. The sources of data for this assessment include (1) the results of monitoring from April 2010 to November 2011 at station Duck Creek 1 (STORET station 13030001) and (2) results of an IDNR Fisheries Bureau trout reproduction survey updated in February 2012.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 19 samples collected during the recreational season of 2010 (530 orgs/100 ml), exceeded the Class A1 criterion of 126 orgs/100 ml. The geometric mean of the 11 samples collected during 2011 (90 orgs/100 ml), however, was below the Class A1 criterion. Sixteen of the combined 30 samples (53%) exceeded Iowa’s 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 is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). [Note: Results of bacteria monitoring suggest that, if this stream were designated for Class B(CW1)/A1/A2 uses, the Class A2 uses would be assessed as “fully supporting” based on the available data for indicator bacteria.]
The aquatic life uses of this stream segment are assessed (monitored) as “fully supporting”. Results of chemical/physical water quality monitoring conducted at site Duck Creek 1 (STORET station 13030001) from June to November 2011 show no violations of Class B(CW1) water quality criteria for dissolved oxygen (seven samples) or temperature (11 samples) collected. The maximum temperature was 18.2C, and the minimum dissolved oxygen was 7 mg/l, thus suggesting that this stream segment functions as a coldwater stream.
Based on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, the presumptive aquatic life uses are assessed as "fully supported". According to the updated summary, Duck Creek is in the group of Iowa coldwater streams that supports natural reproduction of trout. Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout Streams that exhibit fairly consistent natural reproduction and maintain a viable population of the listed species without any stocking.
