Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 2002 and 2004 (2) IDNR/UHL ambient water quality monitoring conducted in 2001 in support of TMDL development, and (3) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (monitored) as "partially supported " based on results of IDNR/UHL biological (biocriteria) sampling in 2002 and 2004. This assessment is also based on results of IDNR/UHL ambient monthly water quality monitoring conducted from March to November 2001 in support of TMDL development. Fish consumption uses are assessed (monitored) as "fully supported" based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2004.
EXPLANATION: The assessment of the Class B(WW) aquatic life uses was based on data collected in 2002 and 2004 as part of the DNR/UHL stream biocriteria project. The 2002 FIBI score was 61 (good) and the BMIBI score was 63 (good). The 2004 FIBI score was 44 (fair) and the BMIBI score was 36 (fair). The FIBI average was 52.5 and the BMIBI average was 49.5. The aquatic life use support was assessed as partially supporting (= PS), based on a comparison of the FIBI and 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 non-riffle FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.
Results of monitoring conducted in 2001 in support of TMDL development for the downstream segment of Black Hawk Creek show no violations of state water quality criteria for conventional parameters in the nine monthly samples collected between March and November 2001. Biological monitoring is better able to reflect cumulative impacts of water quality over time and thus is believed to more accurately represent water quality conditions of this segment of Black Hawk Creek than do results from the monthly TMDL monitoring site.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hudson in 2004 (see the assessment for previous reporting cycles for information on previous RAFT monitoring in this stream segment).. 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: 0.072 ppm; total PCBs: 0.092 ppm; and technical chlordane: 0.044 ppm. Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.098 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 2004 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.
