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 2000, 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 "fully supporting" based on results of fish contaminant monitoring in 2000. 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 2000.
EXPLANATION: The Class A uses were assessed (evaluated) as "not supported" due to high levels of indicator bacteria (fecal coliforms) that violate state water quality criteria. For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." Due to the lack of sample flow data, and due to the lack of a USGS gaging station near the MPCA monitoring site, data for both sample flow and long-term monthly averages were taken from the USGS gaging station at Charles City. Five of the 7 samples collected from the Austin, MN station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these five non-runoff-affected samples (231 orgs/100ml) is above the Iowa Class A water quality criterion of 200 orgs/100ml. In addition, one of the five samples (20%) contained a level of fecal coliform bacteria that exceeded the U.S. EPA-recommended single-sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean is greater than 200 orgs/100ml, the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Because less than 10 non-flow affected samples were available for this assessment, the assessment type is considered "evaluated"; thus, this assessment is not of sufficient quality to support a Section 303(d) listing.
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 as "fully supporting" based on results of EPA/IDNR fish tissue (RAFT) monitoring conducted west of Osage in 2000. Levels of all contaminants in the composite samples of fillets from channel catfish and smallmouth bass were below ½ of the respective FDA action levels and IDNR levels of concern.
