West Fork Cedar River IA 02-WFC-801

Assessment Comments

Assessment is based on results of (1) IDNR ambient monthly monitoring at Finchford from 2002-04 and (2) IDNR/UHL biological (biocriteria) sampling from 2000-2002.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported " based on results of both chemical/physical and biological monitoring.   Fish consumption uses are assessed as “fully supported” based on fish contaminant monitoring in 2002.   Sources of data for this assessment include (1) the results of IDNR/UHL ambient monthly water quality monitoring conducted on the West Fork Cedar River at Finchford (IDNR station 10070003) during the 2002-2004 assessment period, (2) results of IDNR/UHL biological monitoring conducted from 2000-2002 as part of the IDNR biocriteria project, and (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2002.  

EXPLANATION:  None of the approximately 50 samples collected during the 2002-2004 assessment period at the IDNR monthly station violated Class B(WW) water quality criteria for pH or ammonia-nitrogen; no violations occurred in the approximately 10 samples analyzed for pesticides and toxic metals.   One of 51 samples, however, did violate the Class B(WW) criterion for dissolved oxygen.   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses.   Thus, the percentages of violations of the dissolved oxygen criterion at this station (2%) does not suggest an impairment of aquatic life uses in this stream segment.

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 samples analyzed for DDE at the IDNR station from 2000 through 2004 has contained a detectable level of DDE.   Based on these results, the Class B(WW) aquatic life uses of this river segment would be assessed as "fully supported."  

Results of IDNR/UHL biological monitoring in 2002 suggest “partial support” of the Class B(WW) 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 (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 2000-2002 BMIBI scores was 39, 45, 50 (fair).   The BMIBI average was 44.7.   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI 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 artificial substrate BMIBI BIC for this ecoregion is 52.

Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Allison, Iowa, in 2002.   The composite samples of fillets from channel catfish and smallmouth bass had low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.105 ppm; total PCBs: 0.094 ppm; and technical chlordane: 0.045 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.08 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.03 ppm.

The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses.   Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa.   In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol.   This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol).   Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses.   This scenario, however, does not apply to the fish contaminant data generated from the 2002 RAFT sampling conducted in this assessment segment:  the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.