Assessment Comments
Assessment is based on (1) water quality monitoring conducted by LTRMP office, Bellevue, IA. and (2) 1999 Biocriteria sampling: Fish IBI= 17(poor), BM-IBI= 42(fair). See attached document for details.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed as "partially supported." Fish consumption uses remain "not assessed." The sources of data for this assessment include (1) results of IDNR/UHL biological monitoring near Teeds Grove in 1999 and (2) results of routine water quality monitoring conducted in 2000 and 2001 by IDNR staff of the Upper Mississippi River "Long-Term Resource Monitoring Program (LTRMP) at Bellevue, IA. EXPLANATION: The assessment of the Class B(WW) uses is based on results of IDNR/LTRMP chemical/physical monitoring and IDNR / UHL biological monitoring. Results of the 1999 biocriteria sampling by IDNR and UHL show that the fish IBI was "poor" (=17), while the IBI for benthic macroinvertebrates was only "fair" (=42). These results justify the lowering of the assessment of support of the Class B(WW) uses from "partially supported" to "not supported." based on a comparison of the most recent F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.
In addition to biological monitoring, the IDNR/LTRMP staff at Bellevue supplied water quality data for 56 samples collected from Elk River during the period October 1999 through November 2001. Samples were collected approximately every two weeks; samples were collected during all months of the year. The parameters analyzed included dissolved oxygen, pH, ammonia-nitrogen, total phosphorus, total nitrogen, total suspended solids, and chlorophyll. A summary of these data show no violations of the Class B(WW) water quality criteria for temperature, pH, dissolved oxygen, or ammonia-nitrogen in the 56 samples collected. A comparison of water quality data between the 1998-99 and 2000-01 periods suggests very little change over this four-year period. Average, maximum, and minimum levels of dissolved oxygen, pH, total phosphorus, and total nitrogen were nearly identical between the two period. For example, average and median levels of total phosphorus were unchanged from the 1998-1999 period, with a mean of 0.19 mg/l and median of 0.12 mg/l. Similarly, levels of total nitrogen in the 1998-99 period were nearly identical to those of the 2000-01 period, with average levels in the two periods of 10.9 and 11.8 mg/l, respectively. . Although these nutrient values are moderately high, they are more or less typical for Iowa streams and do not suggest serious water quality problems.
Despite the results of chemical monitoring that suggest good water quality in Elk River ("full support"), the results of biological monitoring suggest an impairment ("non-support") of the aquatic life uses. Because stream biota (fish and aquatic macroinvertebrates) integrate water quality impacts over the long-term, the results of biological monitoring are typically weighted more than results of chemical monitoring when determining support of aquatic life uses for purposes of Section 305(b) reporting. This approach is consistent with recommendations in U.S. EPA's guidelines for Section 305(b) reporting (see U.S. EPA 1997b, page 3-21). Thus, considering the "full support" suggested by results of chemical monitoring, and the "non-support" suggested by results of biological monitoring, the aquatic life use of this segment of Elk River are assessed as "partially supported" for the 2002 report. This assessment is also consistent with results of previous biological monitoring that has suggested impairments to the aquatic life uses of this river segment (see assessments for the 1998 and 2000 reports above).
Fish consumption uses remain "not assessed" due to the lack of monitoring in this river reach.
