Assessment Comments
Assessment is based on: (1) the results of monthly monitoring at the IDNR fixed ambient station at the Highway 38 bridge north of Olin from 2004 through 2006 (STORET station 10530001), (2) information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000) and (3) fish sampling conducted by IDNR Fisheries Bureau in 2003.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of ambient chemical/physical/bacterial water quality monitoring from 2004-06. The Class B(WW1) aquatic life remain assessed (evaluated) 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 from 2004 through 2006 (STORET station 10530001), (2) information from the report "Statewide Assessment of Freshwater Mussels (Bivalva, Unionidae) in Iowa Streams" by Arbuckle et al. (2000) and (3) IDNR Fisheries bureau sampling in 2003. This assessment is also used for the adjacent downstream segment (IA 01-WPS-0010-4) except for the Fisheries Bureau fish sampling.
EXPLANATION: The Class A1 uses are 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 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 2004, 2005, and 2006 showed that the geometric mean level of indicator bacteria (E. coli) in the 24 samples collected (236 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 criterion 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). Note: the summary statistics for the current (2008 cycle are nearly identical to the summary for the previous (2006) cycle: the geometric mean values are nearly identical (278 orgs/100 ml for the 2004 cycle; 236 orgs/100 ml for the 2008 cycle), and 12 of 24 samples (50%) exceeded the single-sample during assessment period for both the 2006 and 2008 cycles. These results suggest relatively constant levels of indicator bacteria in this assessment segment.
Despite the results of bacterial monitoring that suggest impairment of the Class A1 uses, the results of ambient water quality suggest “full support” of the Class B(WW1) aquatic life uses due to (1) the lack of violations of Iowa Class B(WW1) water quality criteria for dissolved oxygen and ammonia-nitrogen in the 36 samples collected from January 2004 through November 2006 at the IDNR fixed ambient station near Olin and (2) the lack of violations of Class B(WW1) water quality criteria in the 10 samples from this station analyzed for pesticides and toxic metals during the 2004-2006 period. One of the 36 samples analyzed for pH did exceed the Iowa Water Quality criterion to protect Class A1 and Class B(WW1) uses: the pH in the sample collected on November 5, 2003, was 9.3 units, thus exceeding the Class A1/B(WW1) criterion of 9.0 pH units. 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 does not suggest impairment of aquatic life or primary contact recreation uses. Thus, the percentage of violations of the pH criterion at this station does not suggest an impairment of designated 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 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.
Contrary to the results from the mussel results, the results of the 2003 IDNR Fisheries bureau fish sampling suggest this segment is fully supporting (evaluated) its aquatic life uses. This evaluated biological assessment was based on data collected in 2003 by the IDNR Fisheries Bureau. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2003 FIBI score was 46 (fair). The aquatic life use support was assessed (evaluated) as Fully Supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004. The FIBI BIC for this ecoregion is 36. This assessment is considered evaluated because the drainage area (1596 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
Fish consumption uses were not assessed due to the lack of fish contaminant monitoring information for this river reach.
