Bonnell Creek IA 03-SKD-1868

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was classified only for general 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 and for Class B(WW1) aquatic life uses. According to the Iowa Water Quality Standards, all perennial rivers and streams and all intermittent streams with perennial pools that are not specifically listed in the Iowa surface water classification are designated as Class A1 and Class B(WW1) waters. Thus, for the current assessment, perennial flow is presumed, and the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW1) water quality criteria.]

The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supporting” based on biological data collected in 2002 as part of the IDNR/SHL stream REMAP project.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 2002 FIBI score was 34 (fair) and the BMIBI score was 47 (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 from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41.   Even though this site passed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it is a small headwater stream and doesn’t fall in the calibrated watershed size.

The assessment type is considered "evaluated" (relatively lower confidence assessment) due to the uncertainty of using biological assessment methods developed for Class B(WW2) and wadeable Class B(WW1) streams for assessing aquatic life conditions in small headwater stream segments.   Also, this assessment is considered of lower confidence (evaluated) as opposed to higher confidence (monitored) because the data from the 2002 biological sampling are now older than five years, thus, these data are considered less able to accurately characterize current water quality conditions than would be more recent data.