Assessment Comments
Assessment remains based on (1) results of a fish kill investigation in August 2007, and (2) results of 1997, 2003 & 2004 IDNR/UHL biological monitoring data: FIBI = 55, 52 (good) and 43 (fair); BMIBI = 59, 67 (good) and 48 (fair). FIBI BIC = 36; BMIBI BIC = 51.
Basis for Assessment
Note: Prior to the 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, 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 (2012) 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 data for indicator bacteria upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" due to a fish kill in August 2007. The sources of information for this assessment include (1) results of a fish kill investigation in August 2007 and (2) results of IDNR/UHL biological sampling in 1997, 2003 and 2004.
EXPLANATION: The assessment of the Class B(WW2) aquatic life uses is, in part, based on data collected in 1997, 2003 and 2004 as part of the IDNR/UHL stream biocriteria and REMAP projects. A series of biological metrics which reflect 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 and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1997 FIBI score was 55 (good) and the 1997 BMIBI score was 59 (good). The 2003 FIBI score was 52 (good) and the 2003 BMIBI score was 67 (good). The 2004 REMAP FIBI score was 43 (fair) and the 2004 REMAP BMIBI score was 48 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 2/3 times in the last 14 years.
While results of IDNR/UHL biological sampling suggest "full support" of the Class B(WW2) aquatic life uses, the occurrence of a fish kill in 2007 suggests that the aquatic life uses should be assessed (evaluated) as "partially supported." The kill occurred on or before August 21, 2007; no cause was identified for this fish kill. Approximately 3,497 fish were killed on August 21 and 22, 2007. The kill affected 5 miles of the stream from 2 miles south of Monmouth to the south edge of Baldwin. The estimated value of the fish was $11,145.37.
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 in a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous 14 years; however, multiple samples were not collected during a five-year period. Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Despite this change in assessment methodology and type, this waterbody remains in IR Category 3b based on the 2007 fishkill.
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 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 Integrated Report.
