Little Rock River IA 06-BSR-1798

Assessment Comments

Assessment is based on results of (1) biological monitoring conducted by IDNR Fisheries in 2000 and (2) IDNR/UHL ambient water quality monitoring conducted in 2002 and 2003 in support of TMDL development.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses are assessed as “fully supported” based on (1) results of biological monitoring for fish conducted in 2002 by the IDNR Fisheries Bureau and (2) results of IDNR/UHL ambient water quality monitoring conducted during the 2002-2004 assessment period as part of TMDL monitoring (TMDL station 6; STORET station 11600005).

EXPLANATION:  This assessment was based on data collected in 2000 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 2000 FIBI was 62 (good).   The aquatic life use support was assessed as Fully Supporting (=FS), based on a comparison of the FIBI score 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 43.

Similarly, results of chemical/physical water quality monitoring conducted by IDNR/UHL from March 2002 through December 2003 in support of TMDL development suggest relatively good water quality in this stream.   None of the 21 samples collected had levels of dissolved oxygen, pH, or ammonia-nitrogen that violated state water quality standards (these samples were not analyzed for toxic metals or pesticides).   These results, although somewhat limited in terms of parameter coverage, suggest "full support" of the Class B(LR) aquatic life uses.