West Fork Cedar River IA 02-WFC-801

Assessment Comments

Assessment is based on results of (1) IDNR ambient monthly monitoring at Finchford from 2000-02 and (2) IDNR/UHL biocriteria sampling in 2002.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "fully supported / threatened" based on results of biological monitoring.   Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.   Sources of data for this assessment include (1) the results of IDNR ambient monthly water quality monitoring conducted on the West Fork Cedar River at Finchford during the 2000-2002 assessment period and (2) results of IDNR/UHL biological monitoring conducted in 2002 as part of the IDNR biocriteria project.  

EXPLANATION:  None of the 42 samples collected during the 2000-2002 assessment period at the IDNR monthly station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen; no violations occurred in the nine samples analyzed for pesticides.   This river segment continues to demonstrate above average water quality conditions for Iowa rivers.   Although monitoring conducted by USGS from 1996 to 1998 showed that one of 26 samples contained DDE above the Class B(WW) chronic criterion (see assessment for the 2000 report), none of the six samples analyzed for DDE at the IDNR station during the 2000-2002 assessment period contained a detectable level of DDE.   Based on these results, the Class B(WW) aquatic life uses of this river segment are assessed as "fully supported."  

Despite results of IDNR/UHL ambient chemical/physical monitoring that suggest “full support” of the aquatic life uses, results of IDNR/UHL biological monitoring in 2002 suggest a “threat” to the full support of these uses.   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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2002 Fish IBI score was unavailable and the BM-IBI score was 57 (good).   The aquatic life use support was assessed (evaluated) as fully supporting / threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established for previous Section 305(b) reports.   The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.

Support of the fish consumption uses remains "not assessed" due to the lack of recent fish contaminant monitoring in this river reach.