Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (REMAP) sampling in 2002, (2) water quality monitoring conducted in 2001 by Minnesota Pollution Control Agency at Gordonville, MN, approximately 1 mi N of the IA/MN state line, and (3) U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Northwood in 1999.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as “fully supported / threatened” based on (1) results of monitoring for indicator bacteria and (2) reports of nuisance levels of algae in this river segment. The Class B(WW) aquatic life uses are assessed (evaluated) as “fully supported / threatened” based on (1) results of biological monitoring in 2002 and (2) based on anecdotal information that suggests nuisance growth of aquatic plants (algae) occur in this segment of the Shell Rock River. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 1999. Sources of data for this assessment include (1) results of IDNR/UHL biological (REMAP) monitoring in 2002, (2) results of ambient chemical/physical monitoring by the Minnesota Pollution Control Agency (MPCA) near Gordonsville, MN in 2000 and 2001, (3) anecdotal information on nuisance algal blooms and best professional judgment used to develop assessments for the 1998 and 2000 reports, and (4) results of U.S. EPA/IDNR fish contaminant monitoring near Northwood in 1999.
EXPLANATION: The results of monitoring for indicator bacteria by MPCA during the 2001 recreation season suggest that the Class A (primary contact) uses are “fully supported / threatened.” For purposes of Section 305(b) assessments, IDNR 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." Due to the lack of flow data for the MPCA samples, IDNR was not able to identify results that may have been affected my surface runoff. Thus, this assessment is based on an evaluation of the available data. The geometric mean level of indicator bacteria (fecal coliforms) in the seven samples (113 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml. Two of the 7 samples exceeded the U.S. EPA-recommended single-sample maximum value of 400 orgs/100 ml. Based on the relatively low geometric mean, and based on the lack of sufficient data to develop a “monitored” assessment, the Class A uses are assessed (evaluated) as “fully supporting / threatened.” In addition, anecdotal information that suggests that nuisance growth of aquatic plants occurs during summer months in this segment of the Shell Rock 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 ambient chemical/physical monitoring from MPCA suggest that the Class B(WW) aquatic life uses are “fully supported.” None of the 10 samples collected from October 2000 through September 2001 violated state water quality criteria for dissolved oxygen, temperature, pH, or ammonia nitrogen. Results of IDNR/UHL biological monitoring, however, suggest that these uses should be assesses (monitored) as “fully supported / threatened.” This assessment was based on data collected in 2002 as part of the DNR/UHL REMAP project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and 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) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2002 Fish IBI score was not available and the BM-IBI score was 56 (good). The aquatic life use support was assessed (evaluated) as fully supported/threatened (=FS/T), based on a comparison of the BM-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. The Class B(WW) uses also 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).
Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S. EPA / IDNR fish tissue (RAFT) monitoring near Northwood in 1999.
