Baldwin Creek IA 02-CED-6328

Assessment Comments

Assessment based on 2011 IDNR/SHL biological sampling data: FIBI = 53 (good), BMIBI = 59 (good). FIBI BIC = 36 and BMIBI BIC = 51.

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 (2014) assessment, 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 are “not assessed” (IR 3a) due to the lack of water quality information upon which to base an assessment.  The presumptive Class B(WW1) aquatic life uses of the waterbody are assessed (evaluated) as “fully supporting” (IR 2a) based on results of IDNR/SHL biological sampling conducted in 2011.  

EXPLANATION: The (evaluated) assessment of the presumptive Class B(WW1) aquatic life uses was based on data collected in 2011 as part of the IDNR/SHL headwater stream sampling 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 2011 FIBI score was 53 (good) and the BMIBI score was 59 (good).  The aquatic life use support was assessed (evaluated) 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 36 and the BMIBI BIC for this ecoregion is 51.  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.