Assessment Comments
2014: Assessment remains based on: (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 and (2) results of ambient water quality monitoring near Rockford by USGS from April to December 2004. 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.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (evaluated) as “partially supported” (IR 4a) based on monitoring for indicator bacteria (E. coli) from 2002-2004. The Class B(WW1) aquatic life uses remain assessed (evaluated) as "fully supported" (IR 2a) based on results of ambient water quality monitoring conducted at Rockford from 2002-2004. The assessment type is changed from “monitored” (higher confidence assessment) to “evaluated” (lower confidence assessment) due to the age of the data (greater than five years. 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 and (2) results of ambient water quality monitoring near Rockford by USGS from April to December 2004. 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.
Note: A TMDL for indicator bacteria in this segment of the Shell Rock River was prepared by and approved by EPA in February 2010. Because all Section 303(d) impairments identified for the 2008 assessment/listing cycle (indicator bacteria) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved) of Iowa’s Integrated Report.
EXPLANATION: The Class A1 uses remain assessed (monitored) as "partially supported” due to levels of indicator bacteria (E. coli) that exceed state criteria. This assessment remains based on results of IDNR/UHL ambient water quality monitoring for E. coli. 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) was well-below the Iowa Class A1 water quality criterion of 126 orgs/100ml and indicated relatively low levels of bacteria in this river reach (note: results of ambient (IDNR/UHL) monitoring downriver in Shell Rock River segment IA 02-SHL-0010_2 also suggest low levels of E. coli). Five of the 23 samples, however, exceeded Iowa’s 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 of E. coli is less than the applicable state criteria, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Thus, these data suggest that the Class A1 uses should be assessed as “fully supported.” These EPA guidelines, however, also suggest that if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the monitoring data from 2002-04 suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.”
Previous assessments for this segment of the Shell Rock River have suggested possible impacts from 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." This information is out-of-date (older than 10 years), and no additional complaints of problems with aquatic vegetation in this segment of the Shell Rock River have been received.
The Class B(WW1) uses remain assessed (evaluated) as "fully supported" based on results of (1) IDNR/UHL and (2) USGS ambient water quality monitoring conducted during the 2002-2004 period. Results of IDNR/UHL monitoring showed 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). Similarly, results of USGS monitoring showed no violations of Class B(WW1) criteria for ammonia, dissolved oxygen, or pH in the nine samples collected from April to December 2004.
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 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.
Previous assessments for this segment were also partially based on data collected in 1999 as part of an IDNR 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 (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 1999 evaluated FIBI was 42 (fair). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI 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 1994-2004. 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. Because the data upon which this assessment was based are now more than ten years old, they are no longer being used for purposes of assessment. As water quality data age, they are less able to represent current water quality conditions. As data age beyond ten years, their ability to represent current water quality conditions is increasing suspect. Additional monitoring is needed in this assessment segment to update status of its aquatic communities.
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
