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 2004 through October 2006, (2) results of IDNR/UHL biological (biocriteria) monitoring in 2000 and 2007 and (3) an updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in May 2006.
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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), 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 remain assessed (monitored) as “partially supported” based on results of bacteria monitoring from 2004-06. The presumptive Class A2 (secondary contact recreation) use remain assessed (monitored) as “fully supported.” The Class B(CW) coldwater aquatic life uses are 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 May 2006. 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 2004 through October 2006, (2) results of IDNR/UHL biological (biocriteria) monitoring in 2000 and 2007, and (3) information from a 2006 summary of trout reproduction in Iowa’s coldwater streams.
EXPLANATION: The presumptive Class A1 (primary contact recreation) remain assessed (monitored) as impaired due to violations of Iowa’s water quality criteria for indicator bacteria. The presumptive Class A2 (secondary contact recreation) uses, however, remain assessed (monitored) as “fully supported.” The geometric mean of E.coli in the 20 samples collected at UIRW site 24 during the recreational seasons of 2004 through 2006 was 85 orgs/100 ml. This geometric mean is well below the Class A1 criterion of 126 orgs/100 ml and is far below the Class A2 criterion of 630 orgs/100 ml. Five of the 20 samples (25%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.; none of the 20 samples exceeded Iowa’s Class A2 single-sample maximum criterion (2,880 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). Also, according to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the single-sample maximum criterion, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the results from UIRW Site 24 suggest that, although the geometric is well below the Class A1 criterion, significantly more than 10% of the samples exceed the Class A1 single-sample maximum criterion. Thus, the Class A1 uses should be assessed as “partially supported.” In terms of Class A2 criteria, however, the geometric mean and the number of samples exceeding the Class A2 single-sample maximum criterion both meet the Class A2 criteria; thus, these results suggest that the Class A2 uses should be assessed as “fully supported.”
The Class B(CW1) aquatic life uses are assessed (evaluated) as "fully supported." This assessment was based on data collected in 2000 and 2007 as part of the IDNR/UHL stream biocriteria project. A series of eight (8) coldwater biological indicators, which reflect stream water quality and habitat integrity, were calculated from the biocriteria sampling data and supplemental IDNR Fisheries Bureau data. The coldwater biological indicators are based on the numbers and types of coldwater benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. Sites that score 5-8 are Fully Supporting (FS), sites that score 2-4 are Partially Supporting (PS), and sites that score 0-1 are Not Supporting (NS). The 2000 coldwater biological indicator score was 7/8 and the 2007 score was 8/8. The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the coldwater biological indicator score with biological assessment criteria established for this Section 305(b) report. The coldwater biological indicators were determined from a statistical analysis of data collected at coldwater stream ecoregion reference sites from 1994-2008 and with assistance from the IDNR Fisheries Bureau.
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 nine years (2000-2008); however, the multiple samples were not collected during 2004-2008. 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 the listed species without any stocking. 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.
