Assessment Comments
Assessment based on (1) results of IDNR/SHL biological sampling in 2007, 2010 and 2011 (CBI = 50, 53 and 63) and (2) a summary of trout reproduction in Iowa streams prepared by IDNR Fisheries in 2012.
Basis for Assessment
[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses. This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses and presumptive Class A2 (secondary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of data for indicator bacteria upon which to base an assessment. The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as "fully supported" (IR 2a) based on (1) biological sampling conducted in 2007, 2010 and 2011 and (2) a summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in 2012. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this stream segment.
EXPLANATION: The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007, 2010 and 2011 as part of the IDNR/SHL coldwater stream sampling project. A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach. The biological metrics were combined to make a coldwater benthic index (CBI). The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2007 CBI score was 53, the 2010 score was 50 and the 2011 score was 63. The aquatic life use support was assessed (monitored) as fully supporting (=FS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report. The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011. The CW BIC is 60 and this segment passed the CW BIC 1/3 times in a six-year period (2007-2012). IDNR normally requires a segment to have a simple majority of passing scores from multiple years in a five-year period to be considered fully supporting. 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 2008 and 2012 to be considered “monitored”. This assessment used multiple samples collected in the previous six years (2007-2012) because the two samples that were collected in 2010/2011 could not complete the assessment (one passed, one failed). Additionally, this assessment of Burr Oak Creek includes the professional judgment of IDNR staff incorporating an in-depth analysis of the metric scores, location of the stream (ecoregion) and the fish sampling that occurred at the time the benthic macroinvertebrates were sampled. This segment is located in the 47c ecoregion while all of the CW reference sites are located in the 52b ecoregion. Additionally, the fish sampling conducted at this segment combined with the natural reproduction data (see below) indicate a healthy trout population in this segment.
In addition, based on an updated summary of trout reproduction in Iowa streams prepared by the IDNR Fisheries Bureau in February 2012, the Class B(CW1) uses remain assessed as "fully supported". According to the updated summary, Burr Oak 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 recent, but inconsistent reproductive success and that are generally not capable of maintaining a viable population of brown trout at this time. This assessment is consistent with previous assessments of the ability of this stream to support natural reproduction of trout.
Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.
