Assessment Comments
Assessment is based on (1) results from IDNR monthly monitoring near Olin in Jones Co and (2) results of statewide survey of freshwater mussels.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment IA 01-WPS-0010-0, which extended 95 miles from the mouth of Wapsipinicon River to its confluence with Buffalo Creek at Anamosa, was split into five subsegments: (1) mouth to Silver Creek near DeWitt, Clinton Co. (IA 01-WPS-0010-1), (2) Silver Creek to Rock Creek south of Wheatland, Clinton Co. (IA 01-WPS-0010-2), (3) Rock Creek to Plum Creek southwest of Lost Nation in Clinton Co. (IA 01-WPS-0010-3), (4) Plum Creek to Walnut Creek near Olin, Jones Co. (IA 01-WPS-0010-4), and (5) Walnut Creek to Buffalo Creek at Anamosa (IA 01-WPS-0010-5). See assessment information for segment IA 01-WPS-0010-1 (mouth to Silver Creek near DeWitt) for previous Section 305(b) assessments for this river reach.]
SUMMARY: The Class A (primary contact recreation) uses were assessed as "fully supported." The Class B(WW) aquatic life were assessed as "fully supported / threatened." Fish consumption uses were not assessed. The sources of data for this assessment include (1) the results of montly monitoring at the IDNR fixed ambient station at the Highway 38 bridge north of Olin in 2000 and 2001 and (2) information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000). 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 15 samples were collected at flows greater than the monthly mean plus one standard deviation of this average and were thus considered "materially affected by surface runoff." Results of IDNR monitroing in the recreational seasons of 2000 and 2001 showed that the geometric mean level of indicator bacteria (fecal coliforms) in the 9 non-runoff-affected samples (129 orgs/100ml) was below the Iowa Class A water quality criterion of 200 orgs/100ml. One of the 9 samples (11%) 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 samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are only "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Due, however, to (1) the lack of sufficient data points for developing a "monitored" assessment (according to DNR's 305(b) assessment methodology, "monitored" assessments require at least 10 non-runoff-affected samples), and (2) the relatively low geometric mean, the Class A uses of this river reach were assessed (evaluated) as "fully supporting." The Class B(WW) aquatic life uses were assessed as "fully supported" due to (1) the lack of violations of Iowa Class B(WW) water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the 24 samples collected from October 1999 through September 2001 at the IDNR fixed ambient station near Olin and (2) the lack of violations of Class B(WW) water quality criteria in the 4 samples from this station analyzed for toxic metals and toxic organic compounds during the 2000-2001 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 four sample sites in this stream segment were 6, 2, 1, and 8 in the 1984-85 period and were 1, 0, 0, and 4, respectively, in the 1998-99 period for an average percent change of -83%. Based on these results, the full support of aquatic life uses suggested by results of IDNR ambient monitoring is downgraded to "fully supported / threatened." 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 were not assessed due to the lack of recent monitoring information for this river reach.
