Howard T. Odum was an American ecologist noted for his pioneering studies of energy flows in ecosystems, and for the application of those same principles to energy use in society. The results from Odum’s seminal research in the 1950s on the energetics of the food web in Silver Springs, Florida, and of the coral reefs of Eniwetok Atoll in the Marshall Islands are found in nearly every text on ecology. Odum’s Environment, Power and Society (1971) was based on a path-breaking application of thermodynamics and ecological energetics to energy flows in human society. Based on the work of Lotka, Odum argued that society faced many of the same energetic constraints that confront other organisms and systems. He introduced the concept of emergy, the amount of solar energy embodied in the products of the biosphere and human society. His work built important theoretical foundations for the subsequent development of the fields of ecological economics and ecological engineering. With his brother Eugene Odum, he was awarded the Crafoord Prize—the equivalent of the Nobel Prize in ecological sciences – from the Royal Swedish Academy of Sciences in 1987.

Odum’s Silver Spring study was the first complete analysis of a natural ecosystem. Silver Spring is a common type of spring-fed stream in Florida, with a constant temperature and chemical composition. Odum mapped in detail all the flow routes to and from the stream. He measured the energy input of sun and rain, and of all organic matter - even those of the bread the tourists threw to the ducks and fish - and then measured the energy that gradually left the spring. In this way he was able to establish the stream's energy budget.

Around 1955, Odum directed studies into radioecology, which included the effects of radiation on the tropical rainforest at El Verde, Puerto Rico, and the coral reefs and ocean ecology at Eniwetok atoll. The Odum brothers were approached by the Atomic Energy Commission to undertake a detailed study of the atoll after nuclear testing. Apparently, the atoll was sufficiently radioactive that upon their arrival the Odums were able to produce an autoradiographic image of a coral head by placing it on photographic paper. These studies were early applications of energy concepts to ecological systems. They were exploring the implications of the laws of thermodynamics when used in these new settings.

In a controversial move, Odum, together with Richard Pinkerton (at the time physicist at the University of Florida), was motivated by Alfred J. Lotka's articles on the energetics of evolution, and subsequently proposed the theory that natural systems tend to operate at an efficiency that produces the maximum power output, not the maximum efficiency. This theory in turn motivated Odum to propose maximum power as a fundamental thermodynamic law. 

In the 1990s in the latter part of his career, H.T. Odum together with David M. Scienceman developed the ideas of emergy, as a specific use of the term Embodied energy, which is defined as the available energy that was used in the work of making a product. Some consider the concept of "emergy", sometimes briefly defined as "energy memory", as one of Odum's more significant contributions. However the concept is neither free from controversy, and not without its critics. Odum looked at natural systems as having been formed by the use of various forms of energy in the past: "emergy is a measure of energy used in the past and thus is different from a measure of energy now. The unit of emergy (past available energy use) is the emjoule to distinguish it from joules used for available energy remaining now." This was then conceived as a principle of maximum empower which might explain the evolution of self-organising open systems. However such a principle has not been empirically demonstrated nor verified by the scientific community.

Sources

• Cleveland, Cutler (Lead Author); Peter Saundry (Topic Editor). 2008. "Odum, Howard T.." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth October 12, 2006; Last revised August 22, 2008; Retrieved September 28, 2009]. 
• Wikipedia Contributors, Howard T. Odum, Wikipedia The Free Encyclopedia, Accessed 28 September 2009.
• Wikipedia Contributors, Embodied energy, Wikipedia The Free Encyclopedia, Accessed 28 September 2009.