Assessment Comments
Assessment based on: (1) results of monitoring for indicator bacteria conducted at Site 24 of the Upper Iowa River Watershed (UIRW) project from April 2008 through October 2010, (2) results of IDNR/SHL biological monitoring in 2000 and 2007 and (3) an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011.
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)).] 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 “not supported” based on results of bacteria monitoring from 2008-10. The presumptive Class A2 (secondary contact recreation) uses, however, are assessed (monitored) as “fully supported” based on this monitoring. The Class B(CW) coldwater aquatic life uses remain assessed (evaluated) as "fully supported" based on results of biological monitoring in 2000 and 2007 and on an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011. Fish consumption uses remain not assessed due to lack of fish contaminant monitoring in this stream segment. Sources of data for this assessment include (1) results of monitoring for indicator bacteria conducted at Site 24 of the Upper Iowa River Watershed (UIRW) project (STORET No. NEIARCD 191910015) from April 2008 through October 2010, (2) results of IDNR/SHL biological monitoring in 2000 and 2007, and (3) information from a 2011 summary of trout reproduction in Iowa’s coldwater streams.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as not supported based on levels of indicator bacteria that exceeded state water quality criteria while the Class A2 (secondary contact recreation) uses are assessed as "fully supported". The geometric means of indicator bacteria (E. coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at UIRW site 24 were as follows: the 2008 geometric mean was 192 orgs/100 ml, the 2009 geometric mean was 26 orgs/100 ml and the 2010 geometric mean was 142 orgs/100 ml. Two of the three geometric means (2008 and 2010) slightly exceed the Class A1 criterion of 126 orgs/100 ml; the 2009 geometric mean is far below the Class A1 criterion of 126 orgs/100 ml. All three geometric means are well below the Class A2 geometric mean criterion of 630 orgs/100 ml. Six of the 21 samples (29%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml; only one of the 21 samples (5%) exceeded the Class A2 single-sample maximum criterion of 2,880 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).
EXPLANATION: The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2000 and 2007 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 2000 CBI score was 59.4 and the 2007 CBI score was 60. In addition, this site had 2 CW fish species comprising ~70% of the fish collected during both samplings. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the CBI scores 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 2/2 times in an eight-year period (2000-2007). IDNR analyzed the all the benthic macroinvertebrate and fish data from this site to make the determination that it passed the criteria.
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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in an eight-year period (2000-2007); however, the multiple samples were not collected a five-year period. Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.
In addition to the biological sampling, an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006, the Class B(CW1) suggests the B(CW1) aquatic life uses are also assessed as "fully supported". According to the updated summary, North Bear 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 brown trout without any stocking (6 miles of the 6.3 mile segment has natural reproduction of brown trout). 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.
