Walnut Creek IA 05-NSH-1449

Assessment Comments

Assessment based on 1998 Fisheries data: FIBI = 29 (fair). FIBI BIC = 31.

Basis for Assessment

[Note:  Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption 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 also now presumptively designated for Class A1 (primary contact recreation) uses.   This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY/EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are "not assessed" due to the lack of information upon which to base an assessment.

The assessment of the Class B(WW1) aquatic life uses was based on data collected in 1998 as part of a DNR Fisheries stream sampling project: Manchester research station.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types of 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).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 evaluated FIBI was 29 (fair).   The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the FIBI 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 31 and this site passes the BIC with the use of the UAV (+7).

The sample data from this segment lack the necessary documentation or metadata to determine whether the data meet quality and completeness criteria required of “monitored” assessments.   Thus, FIBI scores calculated from IDNR Fisheries Bureau sampling data collected in this segment provide useful, but limited evidence of impairment.   With respect to FIBI sample results, the following criteria are considered: sampling conditions; sampling gear; crew size; and length of stream sampled.   One or more of these sample descriptors are not available for the Fisheries Bureau data.   Therefore, considering data completeness and data age issues, IDNR considers the aquatic life use assessment generated by these data as “evaluated” assessments.