controlled experiments. This regional/descriptive approach reflected the pervading notion of lakes as microcosms in that studies on individual lakes usually were multidisciplinary: physical, chemical, and biological measurements were included in most studies, reflecting at least implicitly the idea that lakes are complex organized systems. Efforts at the regional scale during this period also focused on classifying lakes into major types based on a multidimensional set of descriptors. For example, the scheme that classifies lakes according to trophic state (meaning general nutritional status) was developed by August Thienemann and Einar Naumann (see Box 2-4) in the 1920s. According to this scheme, an array of indicators—including a physical measure (transparency), chemical concentrations (of nutrients), and biological characteristics (species types and abundance and primary production)—was used to classify lakes according to their overall nutritional status and productivity. These and other classification efforts provided an impetus for integration and synthesis, leading to generalizations about lakes as ecosystems.

In 1922, the international limnology society, Societas Internationalis Limnologiae (SIL), known in English as the International Association for Theoretical and Applied Limnology, was founded in Germany under the aegis of Thienemann and Naumann. Limnologists in the United States were organized as the Committee on Aquaculture in 1925 and as the Limnological Society of America in 1936. From a starting base of 221 members in 1936, the American society grew to include 4,000 scientists today. It joined with oceanographers to become the American Society of Limnology and Oceanography in 1948; its journal, Limnology and Oceanography, one of the premier research periodicals on lake limnology in the world, was launched in 1955.

MIDCENTURY EXPANSION

Most major universities in North America and Europe had hired limnology professors by the middle of the twentieth century. In almost all cases, these faculty were in departments of biological science (including zoology and botany as well as biology), and the field developed a distinct biological focus. With few exceptions, limnology programs in universities were staffed by one faculty member, and the success of the program rose or fell with the intellectual ability and initiative of that individual. In contrast, natural sciences that are related more directly to resource utilization and economic production (such as forestry, soil science, and fisheries and wildlife) typically developed academic programs with larger and more diverse faculties. Thus, their long-term success was less dependent on that of a single individual.

G. Evelyn Hutchinson, who spent most of his career at Yale University, was a dominant figure in North American limnology during the middle



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