Assessment Comments
Assessment is based on results of (1) IDNR ambient city monitoring in 2000-01, (2) statewide assessment of freshwater mussels, and (3) fish tissue (RAFT) monitoring in 2001.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supported." The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supported." The fish consumption uses are assessed as "fully supported." The sources of data for this assessment are (1) the results of monthly monitoring from November 1999 through September 2001 at the IDNR ambient city monitoring station located downstream from Iowa City at the county road F62 bridge east of Hills, IA, (2) results of the statewide assessment of freshwater mussels in Iowa (Arbuckle et al. 2000), and (3) results of EPA/IDNR fish tissue (RAFT) monitoring at Iowa City in 2001. EXPLANATION: The Class A uses were assessed as "fully supported." 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." Six of the 9 samples collected from the County Road F62 bridge 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 6 non-runoff-affected samples (120 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml. However, one of the 6 samples (17%) 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 more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially 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, however, 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) aquatic life uses were assessed as "partially supported" based on results of the statewide survey of freshwater mussels. Results of monitoring from the IDNR ambient station suggest full support of the Class B(WW) uses. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 14 samples collected or for toxic metals and toxic organic compounds in the two samples analyzed during this biennial period. Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams, however, 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). In general, this comparison showed sharp declines in the numbers of mussel species ("species richness") from the mid-1980s to the late 1990s. For purposes of Section 305(b) reporting, 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. This assessment included the following factors: (1) the percent change in the number of species of freshwater mussels found in the 1984-85 survey versus the 1998-99 survey and (2) the number of mussel species found in the 1998-99 survey. Greater than a 50% decline in species richness from the 1984-84 to the 1998-99 period suggests an impairment of the aquatic life uses. In addition, low species richness in the 1998-99 survey suggests potential impairment. For purposes of Section 305(b) assessment only, staff of the IDNR Water Quality Bureau used results from Arbuckle et al. (2000) to define categories of species richness for Iowa's mussel communities: less than three species indicates low species richness and "nonsupport" or "partial support" of aquatic life use; from four to seven species indicates moderate species richness and potential minor impacts (="fully supported / threatened"); more than seven species indicates high species richness and "full support" of aquatic life uses. Species richness of freshwater mussels at the 9 sample sites in this stream segment were 22, 17, 11, 10, 14, 18, 7, 16, and 6 in the 1984-85 period and were 10, 4, 3, 2, 2, 8, 6, 8, and 4, respectively, in the 1998-99 period for an average percent change of -58%. Based on these results, the full support of aquatic life uses suggested by results of IDNR ambient monitoring is downgraded to "partial support." 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. Additional monitoring is needed to better define the biological status of this stream segment as well as the site-specific causes and sources of impairments of these uses that may exist. Fish consumption uses are assessed as fully supported based on results of EPA/IDNR fish tissue (RAFT) follow-up monitoring in 2001 that showed levels of all contaminants were well below U.S. FDA action levels and IDNR levels of concern. This river segment has a history of relatively high levels of chlordane, and RAFT follow-up monitoring has thus been conducted on an every-other-year basis since 1994 (see assessments for the 1994 through 2000 reports above). The level of chlordane in the sample of channel catfish fillets collected in 2001 was 0.049 mg/kg; this level is much lower that chlordane levels in previous samples (1997: 0.17 mg/kg; 1999: 0.16 mg/kg).
