Assessment Comments
Assessment is based on results of (1) IDNR ambient monthly monitoring at Cedar Bluff from 2002-04, (2) statewide survey of freshwater mussels in 1998-99, and (3) U.S. EPA/IDNR fish contaminant monitoring near Cedar Rapids in 2002 and 2005.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW) aquatic life uses are assessed (monitored) as "not supported" based on results of a 1998-99 statewide survey of freshwater mussels. Fish consumption uses remain assessed (monitored) as “fully supported” based on results of fish contaminant monitoring downstream from Cedar Rapids in 2002 and 2005. The sources of data for this assessment are (1) the results of monthly monitoring from 2002 through 2004 at the IDNR ambient station located at the County Road F28 bridge near Cedar Bluff (station 10160001), (2) results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999, and (3) results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids in 2002 and 2005.
EXPLANATION: The Class A uses were assessed as "not supported" based on results of monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (fecal coliforms) in the 25 samples collected (150 orgs/100ml) slightly exceeds the Iowa Class A water quality criterion of 126 orgs/100ml. According to U.S. EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Eleven of the 25 samples (44%) also exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml.
Results of monitoring from the IDNR ambient station near Cedar Bluff from 2002 through 2004, however, suggest "full support" of these uses. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 36 samples collected or for pesticides and toxic metals in the nine samples analyzed during this biennial period.
Despite the results of ambient water quality monitoring that suggest "full support" of the Class B(WW) uses, results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams suggest a potential impairment to the aquatic life uses of this stream segment. As part of this study, sampling results from 1998 and 1999 (Arbuckle et al. 2000) were compared to results from stream sites surveyed in 1984 and 1985 by Frest (1987). On a statewide basis, this comparison showed sharp declines in the numbers of mussel species ("species richness") in Iowa streams and rivers from the mid-1980s to the late 1990s. Results of this comparison were used by staff of the Iowa DNR Water Quality Bureau to assess the degree to which the aquatic life uses of the sampled stream segments are supported. For purposes of Section 303(d) listing, this assessment was based on the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey. Greater than a 50% decline in species richness from the 1984-85 to the 1998-99 period suggests an impairment of the aquatic life uses. Species richness of freshwater mussels at the five sample site in this river segment were 4, 5, 5, 9, and 5 in the 1984-85 period and were 0, 0, 0, 2, and 0, respectively, in the 1998-99 period for an average percent change of minus 92%. Based on these results, the full support of aquatic life uses suggested by results of IDNR ambient water quality monitoring is downgraded to "not supporting." The confidence level of this assessment is relatively high; thus the assessment type is considered “monitored” in the context of Section 305(b) reporting. According to Iowa DNR’s assessment methodology, waterbodies identified as “impaired” based on a “monitored” assessment are candidates for Section 303(d) listing. As presented by Arbuckle et al. (2000), the potential causes of declines in species richness of Iowa's freshwater mussels include siltation, destabilization of stream substrate, stream flow instability, and high instream levels of nutrients (phosphorus and nitrogen). Their study also suggested the importance of stream shading provided by riparian vegetation to mussel species richness.
Fish consumption uses were assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Cedar Rapids at Palisades Park in 2002 and based on results of RAFT follow-up monitoring in 2005. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. 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 does not apply to the fish contaminant data generated from the 2002 RAFT sampling conducted in this assessment segment.
The 2002 composite samples of fillets from channel catfish and freshwater drum had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.259 ppm; total PCBs: 0.143 ppm; and technical chlordane: 0.034 ppm. Levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.085 ppm; total PCBs: 0.164 ppm; and technical chlordane: 0.032 ppm. The level of mercury in the sample of channel catfish fillets (0.259 ppm), however, exceeded the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory. According to the IDNR/IDPH advisory protocol, the single result from the 2002 sampling on the Cedar River neither warrants issuance of an advisory nor indicates impairment of fish consumption uses. But, this elevated level did indicate the need to conduct additional monitoring to better define contaminant levels in fish from this river segment. Thus, follow-up monitoring was conducted as part of the 2005 RAFT program to better determine (1) levels of mercury in the edible portions (fillets) of fish in this river segment and (2) whether a one-meal-per-week consumption advisory needs to be issued. This (2005) monitoring showed a much lower level of mercury in the composite sample of channel catfish fillets (0.0731 ppm), thus indicating that a consumption advisory is not justified for this river segment. Additional follow-up monitoring will be conducted to continue to monitor levels of mercury in fish from this segment of the Cedar River.
