Assessment Comments
Assessment based on (1) 2007 and 2008 IDNR/UHL biocriteria sampling data and (2) occurrence of a fish kill in July 2002.
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), and due to completion and approval of a use attainability analysis, this segment is also now 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 Class A1 (primary contact recreation) uses and the Class A2 (secondary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment. The Class B(CW1) aquatic life uses are assessed (monitored) as "partially supported" based on results of biological monitoring in 2007 and 2008 conducted as part of the IDNR/UHL stream biocriteria project. Occurrence of a fish kill, possibly caused by runoff by land-applied manure, suggests an additional impairment of the aquatic life uses. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream reach.
EXPLANATION: The assessment of the Class B(CW1) coldwater aquatic life uses was based on data collected in 2007 and 2008 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). Non-fish sampled sites that score 3 or 4 are fully supporting (FS), sites that score 1 or 2 are partially supporting, and sites that score 0 are not supporting (NS). The 2007 coldwater biological indicator score was 1/4 and was a benthic macroinvertebrate only score. The 2008 coldwater biological indicator scores were 1/8 and 3/8. The aquatic life use support was assessed as partially supporting (=PS), 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 use assessment is considered "monitored" because there were two or more samples collected in multiple years from 2004-2008.
In addition, a fish kill occurred on this stream on July 29, 2002. The kill followed heavy rainfall following a long period of hot, dry weather. No specific cause was determined, but runoff from feedlots and/or land applied manure is suspected due to presence of several feedlots in the watershed of this stream. Approximately 0.5 mile of stream was affected, and 184 fish were killed. According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill indicates ongoing impairment of the aquatic life uses. Any existing fish kill (5b) impairment will remain in IR Category 5b until more recent monitoring has shown full recovery of the aquatic communities affected by the kill. Thus, this assessment segment will remain in Category 5b of Iowa’s 2010 Integrated Report.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.
