Assessment Comments
Assessment remains based on results of (1) statewide assessment of freshwater mussels in 1998-99, (2) information from IDNR Fisheries Bureau, (3) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 2001 and 2005, and (4) ambient water quality monitoring by the MN Pollution Control Agency in 2000-01.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "not supported" based on levels of indicator bacteria (fecal coliforms) at the monitoring station three miles south of Austin, MN. The Class B(WW) aquatic life uses are assessed (monitored) as "not supported" based on results of the 1998-99 statewide survey of freshwater mussels. The fish consumption uses were assessed (monitored) as "not supporting" based on results of fish contaminant monitoring in 2001 and 2005 and issuance of a fish consumption advisory in 2006. Sources of information for this assessment include (1) information from the IDNR Fisheries Bureau, (2) results of a 1998-99 statewide assessment of freshwater mussels in Iowa streams (Arbuckle et al. 2000), (3) results of monitoring by the Minnesota Pollution Control Agency (MPCA) three miles south of Austin, MN, and (4) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001 and 2005.
EXPLANATION: The Class A uses remain assessed (evaluated) as "not supported" based on data for indicator bacteria (fecal coliforms) collected at the Minnesota Pollution Control Agency's fixed monitoring station approximately three miles north of the Iowa/Minnesota state line. As shown in the assessment developed for the 2004 reporting/listing cycle, these data suggested that the Class A uses of this segment of the Cedar River should be assessed as "not supported". Despite the fact that Iowa now uses E. coli as the indicator bacterium to assess support of Class A uses, IDNR considers the previous assessment based on levels of fecal coliform as still valid.
The Class B(WW) uses are assessed (monitored) as "not supported" based on information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000). 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 one sample site in this stream segment was 12 in the 1984-85 period and was 0 in the 1998-99 period for a percent change of minus 100%. Based on these results, the aquatic life uses are assessed (monitored) as “not supported.” 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.
Information from the IDNR Fisheries Bureau also suggests potential impairments to the aquatic life uses designated for this river segment. Recent surveys have shown that the smallmouth bass population of the Cedar River from the Iowa/Minnesota state line downriver to St. Ansgar is relatively poor and will not support the "catch and release" fishery planned for this river reach. Potential explanations for this problem include (1) habitat alterations caused by flooding in 1993 and (2) water quality impacts. For example, a pesticide-related fish kill occurred on the Cedar River in March 2001 downstream from the Austin, MN, wastewater treatment plant. Additional monitoring is needed to more accurately characterize the water quality of this river reach.
Fish consumption uses were assessed (monitored) as “not supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Osage in 2001 and in 2005. 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 (IDPH), 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 applies to the fish contaminant data generated from the RAFT sampling conducted in this segment of the Cedar River: levels of mercury in fillet samples of smallmouth bass and walleye from consecutive samplings exceeded advisory trigger levels, thus suggesting the need for a consumption advisory. According to IDNR’s assessment methodology, the existence of a consumption advisory indicates that fish consumption uses should be assessed as “not supported”.
The level of mercury in the composite sample of smallmouth bass fillets (0.305 ppm) from the 2001 RAFT sampling exceeded the IDNR/IDPH trigger level of 0.20 ppm for a one meal per week consumption advisory (this levels is well below the “do not eat” trigger level for mercury of 1.0 ppm). According to the IDNR/IDPH advisory protocol, if two consecutive samplings show that contaminant levels are above the trigger level in fillet samples, issuance of a consumption advisory is justified. Because the level of mercury in composite sample of walleye fillets from the 2005 sampling (0.33 ppm) also exceeded this advisory trigger level, issuance of a fish consumption advisory is justified. This advisory was issued by IDNR and IDPH in January 2006 and covers the reach of the Cedar River from the Highway 218 bridge at Floyd, IA upriver to the Iowa/Minnesota state line.
