Assessment Comments
Assessment is based on (1) results of IDNR/UHL biological (biocriteria) monitoring in 2002: FIBI = 55 (good), BMIBI = 55 (fair) (riffle habitat FIBI BIC = 53, BMIBI BIC = 62) and (2) results of a fish kill investigation in August 2006.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) 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 now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (evaluated) as "partially supported" based on results of a fish kill investigation in August 2006. The assessment is based on (1) results of IDNR/UHL biological (biocriteria) monitoring in 2002: FIBI = 55 (good), BMIBI = 55 (fair). Riffle habitat FIBI BIC = 53, BMIBI BIC = 62, and (2) results of a fish kill investigation in August 2006.
EXPLANATION: The presumptive Class A1 designation was added to this segment of Prairie Creek in 2008; no water quality data or other information are available upon which to base an assessment of support for this use designation.
The Class B(WW2) aquatic life uses are assessed (evaluated) as "partially supported" due to a fish kill in August 2006. The kill occurred on our before August 21, 2006 one mile upstream of Dolliver State Park and was attributed to natural causes (low dissolved oxygen). The partial fish kill of about 200 to 300 minnows, chubs and shiners occurred in a meandered section of the stream through a wooded area. It is speculated that day time oxygen levels in this section of stream were not sufficient to carry through the night time hours and the weaker fish succumbed. Live fish were observed in the same area as dead fish. Live fish were observed both above and below the fish kill segment. Manure or fertilizer releases are not suspected as a reason for the fish kill because ammonia nitrogen levels were not elevated in the stream. No estimate of the value of the fish was made.
According to IDNR’s assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2004-2007) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired.” If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation. Thus, this assessment segment will be placed in Category 3b of Iowa’s 2008 Integrated Report.
Data collected in 2002 as part of the DNR/UHL stream biocriteria project, however, suggest "full support" of the Class B(WW2) uses. The 2002 FIBI score was 55 (good) and the BMIBI score was 55 (fair). The aquatic life use support was assessed as Fully Supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62.
