became somewhat of a minor celebrity in Natal during this time. India In 1932 Hutchinson joined the Yale North India Expedition. He wanted to be the first to make ecological observations of a high-altitude lake, and to compare these with lower-altitude lakes. The work yielded insights into biogeography and new data on high elevation limnology. Most lakes had no fish, and crustaceans were the top predators. In letters to his wife, he described the different water chemistry from the Indian lakes to the South African lakes. He collected hundreds of specimens for analysis by specialists. This expedition provided the material for his first book, The Clear Mirror, in which he described the colors, organisms, ecology, and the people of the Ladakh. Limnology and trophic dynamic energy flow Most of Hutchinson's contributions to American limnology came from research at Linsley Pond in Connecticut. Studies were done on small lakes, such as chemical stratification, oxygen deficits, productivity, and the ecological significance of the oxidation-reduction potential of lake waters. His four volume Treatise on Limnology became a standard for limnology students. Hutchinson expanded the field of limnology, especially in its ecological and biogeochemical aspects. He advocated the use of statistical and mathematical methods in limnology. His postdoctoral associate Raymond Lindeman furthered Hutchinson's model of the trophic dynamic concept. Together they looked at energy flows through the lake in the trophic levels of ecosystems. They followed the energy using Hutchinson's notation system in which each organism was given an integer to mark how many organisms the energy had to go through in order to reach it, this was designated as its trophic level. It then became possible to measure the efficiency of a given system, or the energy losses between ascending trophic levels. Radioisotopes Hutchinson is also recognized as being the first to use radioisotopes as tracers in field experiments. In doing so he along with his graduate student Vaughan Bowen, are credited with creating Radiation Ecology, a brand new major field of ecology. He again turned to Linsley Pond, he released twenty-four portions in two lines and dispersed it uniformly across the water, a week later they collected water across different depths in the lake. They then evaporated and measured the radioactivity, what they found they deemed to be statistically significant. The rest was found to have been taken up by the aquatic plants in the shallow water area of the lake. Ecology