Selected Water Quality Characteristics Of Minimally Impacted Streams From Minnesota's Seven Ecoregions

Data from minimally impacted streams in each ecoregion provide a basis for comparison to existing water quality in streams of concern and an initial basis for establishing water quality goals. For Minnesota, significant differences in water quality have been identified among ecoregions. These differences suggest that evaluating water quality on an ecoregion basis is appropriate and that attainable levels of water quality may vary between regions. As reported in Fandrei, et al. (1988), least impacted sites were selected for each of the seven ecoregions in Minnesota. STORET stream water quality data for the period from 1970 to 1985 was used to characterize stream water quality in each ecoregion. These least impacted sites, or reference sites, have been used to estimate the attainable water quality for an ecoregion. The streams included in Fandrei, et al. (1988) had the following characteristics: 1) at least four years of data; 2) data collected monthly for at least four years; 3) data that provides a reasonable representation of the ecoregion (drainage area should not include large areas of more than one ecoregion); and 4) no nearby point source discharges. Table 1 lists the least impacted sites by ecoregion. These estimates of attainable water quality have been used since 1988. Hughes et al. (1986) refer to areas of least impact as reference watersheds" and feel that reference sites can be used to estimate the best obtainable water quality for a region. The sites in Table 1 are not "reference watersheds" in the classical sense since they were not specifically selected based on their watershed characteristics and then intensively monitored. Rather the data