North Cedar Creek IA 01-YEL-431

Assessment Comments

Assessment based on results of: (1) IDNR/SHL biological sampling data in 2007, 2008 and 2011; (2) water quality and biological sampling conducted in 2000-01 as part of the Sny Magill / Blood Run project; and (3) the February 2012 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 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 (monitored) as "fully supported" (IR 2a) based on the results of biological monitoring conducted in 2007, 2008 and 2011, results of ambient water quality monitoring conducted from 2000-2001 and on the February 2012 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach (IR 3a).   The sources of data for this assessment are results of (1) IDNR/SHL biological sampling conducted in 2007, 2008 and 2011 as part of the stream biocriteria project, (2) water quality monitoring conducted at IDNR station 15220003 from January 2000 to September 2001 as part of the Sny Magill Creek Nonpoint Source Pollution Monitoring Project and (3) the February 2012 summary of trout reproduction in Iowa streams as prepared by the IDNR Fisheries Bureau.   This assessment remains unchanged from the 2012 assessment used for this segment.  

EXPLANATION:  The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2007, 2008 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 scores were 54 and 71, the 2008 scores were 48 and 57 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 2/5 times in a five year period (2007-2011).   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 (monitored).   However, this assessment of North Cedar Creek includes the professional judgment of IDNR staff incorporating an in-depth analysis of the metric scores, sampling conditions and the fish sampling that occurred at the time the benthic macroinvertebrates were sampled.   The 2008 sampling conditions were adversely affected by flooding and if those scores were removed, this segment would have passed the CW BIC 2/3 times and also shown recent improvement in CBI scores.   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, the B(CW1) aquatic life assessment was 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 are assessed as "fully supported".   According to the updated summary, North Cedar 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.  
  
The results of the chemical monitoring conducted on this stream segment in from 2000 through 2001 as part of the Sny Magill Creek Nonpoint Source Project also suggest "full support" of the Class B(CW1) uses.   No violations of Class B(CW1) water quality criteria for dissolved oxygen or temperature occurred in the approximately 90 samples analyzed during this period.  

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.