The above approach to determining the best candidates for lake restoration differs significantly from the traditional one of simply selecting the lakes with the worst trophic states and then spending the available money in an attempt to restore them. The desired trophic state may not be attainable or may require large and continued expenditures of energy and money to be maintained. For example, lake 1 in figure 4.3 is hypereutrophic, and its water quality is among Ohio's poorest. It is located in an ecoregion with rich humic soils in which the principal land use is agricultural. Its attainable trophic state (Figure 4.3) does not differ significantly from its current state. Although management activities (e.g., aeration, weed harvesting, dredging) could improve the lake for recreation, continued loading will refill it with silt and maintain its current trophic state. If this lake were assigned a top priority for restoration without considering its attainable condition, scarce restoration funds could be wasted. Lakes 6, 10, 11, and 12 (Figure 4.3) have much better attainable quality, have deviated significantly from this condition, and are thus better candidates for restoration.

One of the values of the ecoregion concept in lake restoration and management is that it provides a rational basis for setting regional rather than national lake water quality standards. The approach can take into account regional factors related to attainable water quality and thus can be used to designate lakes for protection and to establish lake restoration goals appropriate for each ecoregion.

Stream water quality in some watersheds of an ecoregion, and ultimately lake trophic state, can be greatly improved through changes in land use (e.g., wetland restoration, improved agricultural practices) and through stream restoration itself. In these cases, the additional use of in-lake procedures, such as enhancement of biological controls on algal populations or application of chemicals to control sediment phosphorus release, may improve a lake beyond expectations based on original ecoregion characteristics. Although no lake in the Eastern Corn Belt Plains (ECBP) ecoregion of Indiana and Ohio will look like the oligotrophic lakes of the Northern Lakes and Forests ecoregion of Minnesota, Wisconsin, and Michigan, it is important to recognize that the various ecoregions were defined based on existing land use conditions and that intensive row crop farming is not the native condition of land in the ECBP. If farming became less intensive or less prevalent in the ECBP, or if best management practices became effective in reducing the export of soil and nutrients to streams in the region, land use would become a reduced factor in determining stream quality, and lakes could improve to some degree beyond the conditions currently defined as attainable.

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