physical, chemical, and biological properties; the way in which these properties influence aquatic biota and their growth, dynamics, and productivities; and how the community biological metabolism affects geochemical properties. The aquatic components are integrated in an interactive ecosystem that extends considerably beyond the traditional shoreline boundary of the lake, reservoir, wetland, or stream (Likens, 1984; Wetzel, 1990a; Wetzel and Ward, 1992). Physical, geological, hydrological, chemical, and biological characteristics and processes are examined along a large range of scales, for example, from individual chemical reactions to chemical fluxes within entire ecosystems. A fundamental aspect of aquatic ecosystems that is overlooked frequently, however, is that they are biogeochemical systems; biological processes are essential components of all qualitative and many quantitative aspects of inland aquatic ecosystems.
Past approaches to the study of inland waters were initially descriptive, which was common to many disciplines in the past century. Massive comparative analyses of physical, chemical, and biological properties of inland waters evolved rapidly from 1920 to 1950, particularly in Europe. Greater emphasis was placed on analytical evaluations of intercoupled relationships, particularly among nutrient-phytoplankton interactions, in the subsequent period (1950s-1970s). Simultaneously, great emphasis on feeding relationships emerged in 1970-1980 in concert with marked advances in predator-prey relationships. During the last and present decades, limnologists have begun to recognize the inadequacy of examining pelagic communities independently from the littoral-wetland and land-water interface regions of most lake and river ecosystems. Couplings of all components of the ecosystem, the drainage basin, land-water interface communities, and open-water communities, are critical to both the qualitative and the quantitative understanding of lake and river ecosystems. This essential ecosystem perspective is now being incorporated gradually into the management of inland waters. For a number of complex reasons discussed below, however, the ecosystem perspective is not being incorporated effectively into the undergraduate and graduate training of students in aquatic ecology.
There are two major needs for educating limnologists according to a broad, ecosystem perspective. Foremost, there is a need to promulgate the values of freshwater ecosystems properly in economic terms in our teachings at all levels of education. The importance of the availability