affect ecological processes. During the past 25 years, his work in aquatic ecology has focused on experimental wetland ecology, including the use of wetlands as natural treatment systems for wastewaters.

Odum has authored or coauthored several books that have significantly influenced ecology and related fields. He contributed to the classic ecology text written by his brother, Eugene Odum, also a major figure in ecology in the second half of this century. H. T. Odum's first book, Environment Power and Society (1970), presented a computer language and modeling technique to describe energy flow through ecosystems. The language and modeling approach became the tool of a group of followers who modeled energy flows associated with the movement of commodities in both natural ecosystems and human-dominated systems. This work led to the concept of "embodied energy," since termed "emergy," which accounts for the direct and indirect energy flows (those from "free environmental services" and those supplied by the economy) required to produce a substance. In turn, this led to efforts to conduct economic analyses in terms of energy units.

Odum coined the term ecological engineering in 1962, and he has contributed much to its development as a field distinct from but related to environmental engineering (Mitsch, 1994). He continues to promote the development of university curricula to produce ecological engineers (Odum, 1994). Odum has received many awards, including the Mercer Award of the Ecological Society of America; the AIBS (American Institute of Biological Science) Distinguished Service Award; the Prize of the Institut de la Vie, Paris; and the Crafoord Prize of the Swedish Academy of Sciences. The last two prizes were shared by the two distinguished brothers, H. T. and Eugene.

Experimental Limnology

Experimental lake limnology has involved at least three types of manipulations: (1) stress-response experiments, in which a lake (or a basin in a lake) is treated with a chemical or biological stressor (such as excess nutrients, acid, or a top predator) and the responses of the lake system are studied; (2) hydrologic, physical, chemical, and/or biological manipulations aimed at lake remediation or rehabilitation; and (3) tracer additions to measure rates of physical processes, such as use of radiotracers to follow water movement and noble gases to monitor air-water-gas exchange. Most lake manipulations of the first type employ the modern, expanded concept of the lake as a microcosm in that their aim is to apply a stress to an ecosystem and observe the changes that it causes in various properties of the ecosystem. (Preferably, these properties are measured for a given number of years before the stress is applied, and the experiment continues for several years and includes a recovery phase following the removal of the stress.) Limnologists conducting these experiments typically have studied a wide range of responses—from changes in chemical concentrations



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