Johnson Creek IA 02-CED-559

Assessment Comments

Assessment remains based on 2002 IDNR/SHL biological sampling data: FIBI = 54 (good), BMIBI = 56 (fair). Non-riffle site FIBI BIC = 44, artificial substrate BMIBI BIC = 52.

Basis for Assessment

[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.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses remain "not assessed" (IR 3a) due to the lack of information upon which to base an assessment.   The presumptive aquatic life uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of IDNR/SHL biological (REMAP) sampling in 2002.   The assessment type is considered "evaluated" (relatively lower confidence assessment) (1) due to the uncertainty of using biological assessment methods developed for larger wadeable streams for assessing aquatic life conditions in small headwater stream segments and (2) because the data from the 2002 biological sampling are now older than five years and are thus less able to accurately characterize current water quality conditions than are more recent data.  

EXPLANATION:  The assessment of the aquatic life uses was based on data collected in 2002 as part of the IDNR/SHL 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 54 (good) and the BMIBI score was 56 (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 non-riffle habitat FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.   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.