Assessment Comments
Assessment is based on results of (1) water quality monitoring conducted in 2001 and 2002 by IDNR/UHL in support of TMDL development and (2) biological monitoring by the IDNR Fisheries Bureau in 1999. Data from the 1998-99 statewide survey of freshwater mussels (Arbuckle et al. 2000) was considered but not used for the assessment.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported " due to levels of indicator bacteria that exceed state criteria. In addition, historical anecdotal information that suggests that nuisance growth of aquatic plants occurs during summer months in this segment of this river. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring conducted at Rockford and on results of biological monitoring in 1999. Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment. The sources of data for this assessment are (1) results of monthly monitoring conducted near Rockford (station 11340001; No. 68) from January 2002 to December 2004 by IDNR/UHL in support of TMDL development, (2) anecdotal information and best professional judgment used to develop assessments for the 1998 and 2000 reports, and (3) 1999 IDNR Fisheries sampling results. In addition, results of a statewide survey of freshwater mussels conducted by Iowa State University in 1998 and 1999 (Arbuckle et al. 2000) were evaluated for this assessment.
EXPLANATION: The Class A uses were assessed (monitored) as "partially supported" due to levels of indicator bacteria (E. coli) that exceed state criteria. This assessment is based on results of IDNR/UHL ambient water quality monitoring. 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.
The geometric mean level of indicator bacteria (E. coli) in the 23 samples collected during the recreational seasons of 2002 through 2004 (72 orgs/100ml) is well-below the Iowa Class A water quality criterion of 126 orgs/100ml and indicates relatively low levels of bacteria in this river reach. Five of the 23 samples, however, exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if levels of E. coli exceed the single-sample maximum value in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported” (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.
This segment of the Shell Rock River may also be impacted by excessive growth of aquatic plants (algae) during summer months. This information was originally supplied to IDNR in the context of problems with fishing this segment of river due to algal blooms; however, such conditions suggest potential violation of Iowa's narrative water quality standard protecting against "aesthetically objectionable conditions."
The Class B(WW) uses are assessed (monitored) as "fully supported " based on results of IDNR/UHL ambient water quality monitoring conducted during the 2002-2004 period. Results of this monitoring show no violations of state water quality criteria for conventional parameters (dissolved oxygen, pH, or ammonia) in the 31 monthly samples collected between January 2002 and December 2004 (these samples were not analyzed for toxic metals or pesticides).
This segment of the Shell Rock River was sampled as part of the 1998-99 statewide study of freshwater mussels in Iowa streams and rivers (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. For stream segments having four or more species reported for the 1984-95 survey, 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. The results of this sampling on this segment of the Shell Rock River, however, do not meet IDNR guidelines for developing an assessment of support for the aquatic life uses. Species richness of freshwater mussels at the three sample sites in this segment was 0, 2, and 3 in the 1984-85 period and was 0, 0, and 0 in the 1998-99 period, respectively, for an average 1984-85 species richness of approximately 2 and an average percent change of minus 67%. Based on these results, the aquatic life uses are considered “not assessed” due (1) to IDNR’s assessment methodology in which assessment decisions are developed only for those stream segments having an average of four or more species reported in the 1984-85 (Frest) survey and (2) the difficulty of interpreting status of mussel communities showing relatively low species richness during the both the historical (1984-85) and current (1998-99) surveys.
The assessment was partially based on data collected in 1999 as part of a DNR Fisheries stream sampling project: Manchester research station. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data. The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (F-IBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999 evaluated Fish IBI was 42 (fair). The aquatic life use support was assessed (evaluated) as Partially Supporting (=PS), based on a comparison of the F-IBI score with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001. However, this site was a larger river and was sampled by a boat shocker. Because the biological assessment criteria were calibrated for wadeable streams, it was decided to leave the aquatic life use support assessment as “fully supported” based on the data from IDNR/UHL water quality monitoring.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
