Assessment Comments
Assessment is based on results of water quality monitoring conducted in 2001 and 2002 by IDNR and UHL in support of TMDL development and on 1999 Fisheries data: Fish IBI = 42 (fair). 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 (evaluated) as "fully supported/threatened" due to anecdotal information that suggests that nuisance growth of aquatic plants occurs during summer months in this segment of this river. Results of IDNR/UHL monitoring for indicator bacteria, however, suggest that the Class A uses should be assessed (monitored) as "fully supported." The Class B(WW) aquatic life uses remain assessed (evaluated) as fully supported / threatened" based the anecdotal information suggesting that nuisance growth of aquatic plants (algae) occurs in this segment of the Shell Rock River in summer. 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 from April 2001 to December 2002 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.
EXPLANATION: The Class A (primary contact recreation) uses were assessed (evaluated) as "fully supported/threatened" due to anecdotal information that suggests that nuisance growth of aquatic plants occurs during summer months in this segment of this river. 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." Results of IDNR/UHL water quality monitoring suggest "full support" of the Class A uses. 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." Eleven of the 13 samples collected from the Rockford station during the 2001 and 2002 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these 11 non-runoff-affected samples (62 orgs/100ml) is well-below the Iowa Class A water quality criterion of 200 orgs/100ml. None of the 11 samples had levels of fecal coliforms that 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 the geometric mean is less than 200 orgs/100 ml, and if 10% or less of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW) uses remain assessed (evaluated) as "fully supported / threatened" based on anecdotal information that nutrient enrichment of the river tends to produce nuisance levels of algae in summer (see assessments developed for the 1998 and 2000 reports). Results of IDNR/UHL ambient monitoring conducted near Rockford in 2001 and 2002 in support of TMDL development, however, show no violations of state water quality criteria for conventional parameters in the 20 monthly samples collected between April 2001 and December 2002 (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.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
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/threatened based on the data above.
