Assessment Comments
Assessment is based on results of (1) IDNR monthly monitoring near Olin in Jones Co. from 2002-04 and (2) results of a statewide survey of freshwater mussels from 1998-99.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" based on results of ambient chemical/physical/bacterial water quality monitoring from 2002-04. The Class B(WW) aquatic life remain assessed (monitored) as "partially supported" due to the apparent decimation of freshwater mussel species in this river segment. Fish consumption uses remain not assessed due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) the results of monthly monitoring at the IDNR fixed ambient station at the Highway 38 bridge north of Olin in from 2002 through 2004 (STORET station 10530001) and (2) information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000). This assessment is also used for the adjacent downstream segment (IA 01-WPS-0010-4).
EXPLANATION: The Class A uses were assessed (monitored) as "not supported" based on violations of state criteria 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.
Results of IDNR monitoring in the recreational seasons of 2002, 2003, and 2004 showed that the geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (278 orgs/100ml) was greater than the Iowa Class A water quality criterion of 126 orgs/100ml. Twelve of the 24 samples (50%) exceeded the U.S. EPA-recommended single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and 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).
Despite the results of bacterial monitoring that suggest impairment of the Class A uses, the results of ambient water quality suggest “full support” of the Class B(WW) aquatic life uses due to (1) the lack of violations of Iowa Class B(WW) water quality criteria for dissolved oxygen and ammonia-nitrogen in the 36 samples collected from January 2002 through December 2004 at the IDNR fixed ambient station near Olin and (2) the lack of violations of Class B(WW) water quality criteria in the 10 samples from this station analyzed for pesticides and toxic metals during the 2000-2002 period. One of the 36 samples analyzed for pH did exceed the Iowa Water Quality criterion to protect Class A and Class B uses. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), however, a violation frequency of less than 10 % for conventional parameters such as pH suggest "full support" of aquatic life uses. Thus, the percentages of violations of the pH criterion at these stations do not suggest an impairment of aquatic life uses.
Results from the 1998-99 statewide assessment of freshwater mussels in Iowa streams, however, continue to suggest a potential impairment to the aquatic life uses of this stream segment. The following is the same assessment developed for the 2004 Section 305(b) reporting cycle. 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’s rivers and streams 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. In addition, low species richness in the 1998-99 survey suggests potential impairment. 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. Although species richness declined at all four sites, the average decline at the two sample sites with four or more species in the 1984-85 survey (from 6 to 1 species, and from 8 to 4 species) was 67%. Based on IDNR’s assessment approach, this degree of decline suggests “partial support” of the Class B(WW) aquatic life uses for purposes of both Section 303(d) listing and 303(d) reporting. Based on these results, the full support of aquatic life uses suggested by results of IDNR ambient monitoring is downgraded to "partially supported." 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 in-stream 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. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence). Despite this change in assessment type, the impairment based on declines in the mussel community remains appropriate for IR Category 5b.
Fish consumption uses were not assessed due to the lack of fish contaminant monitoring information for this river reach.
