Middle Fork Little Maquoketa River IA 01-TRK-138

Assessment Comments

Assessment based on 2004 IDNR/SHL biological monitoring data: CBI = 42, 45 and 49; CW BIC = 60.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) 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 also now presumptively designated for Class A1 (primary contact recreation) and Class A2 (secondary contact recreation) uses.   This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.  

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses and presumptive Class A2 (secondary contact recreation) uses remain "not assessed" due to the lack of data for indicator bacteria upon which to base an assessment.   The Class B(CW1) coldwater aquatic life uses remain assessed (evaluated) as "partially supported" based on based on results of REMAP stream biological monitoring in 2004.   Fish consumption uses remain "not assessed."  

EXPLANATION:  The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2004 as part of the IDNR/SHL REMAP stream sampling project.   A series of biological metrics which reflect coldwater 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 that were collected in the stream sampling reach.   The biological metrics were combined to make a coldwater benthic index (CBI).   The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2004 CBI scores were 42, 45 and 49.  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI scores with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 0/3 times in 2004.  

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 a multiple samples collected in 2004.   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).   However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5b and remains on Iowa’s 2012 Section 303(d) list of impaired waters.  

In contrast to the biological sampling data, the updated summary of trout reproduction in Iowa streams prepared by the DNR Fisheries Bureau in February 2011, indicates the Class B(CW1) uses should be assessed "fully supported".   According to the updated summary, Middle Fork Little Maquoketa River (a.k.a.   Bankston Cr.) is in the group of Iowa coldwater streams that supports natural reproduction of trout.   Based on results of surveys by the IDNR Fisheries Bureau, this stream is placed in the category of Iowa trout streams that exhibit fairly consistent natural reproduction and maintain a viable population of brown trout without any stocking.  

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.