It is the policy of the American Association for the Advancement of Science to publish symposia presented at its meetings that "are on subjects of such importance and are of such quality that it can not afford not to publish them." The symposia heretofore published by the Association because they were deemed to measure up to these standards have been The Cancer Problem ( 1937), Tuberculosis and Leprosy ( 1938), Applications of Surface Chemistry in Biology ( 1938), Recent Advances in Chemical Physics ( 1938), Syphilis ( 1938), and Mental Health ( 1939).
This symposium on Problems of Lake Biology was organized by the Limnological Society of America, an affiliated society of the Association. In providing facilities for presenting the symposium and in publishing and distributing it, the Association assists one of its affiliated societies in advancing the interests of a relatively new field of science. The great value of a systematic, comprehensive and documented survey of a rapidly developing science is obvious, for it establishes a solid foundation for future work and presents an outline of a region largely to be explored. This symposium, which was planned by a committee of distinguished specialists in the field, has these qualities.
Perhaps no other biological subject involves a greater variety of interrelated factors than lake biology. On the one hand, there are such physical factors as the size, shape and depth of the lake, the source and temperature of its water, its drainage, the winds that ruffle its surface, the hydrostatic pressures at various depths, and all the complexities of the light of different wave lengths it receives at various depths during the daily and seasonal cycles. The chemical factors are no less numerous and important, among which are the water content of diffused oxygen, carbon dioxide, nitrogen and hydrogen ionizations, and the amounts in solution of compounds of calcium, iron, silicon, phosphorus and other elements. In addition, there are numerous ever-changing and interacting organic compounds.
Finally, there is the cooperating and competing life itself, both plant and animal, both microscopic and macroscopic. In some cases the cooperation is direct--organism with organism or classes of organisms with other classes; the same is true of competition. In other cases the cooperation or competition is indirect--certain organisms or classes of organisms affecting the environment, physical, chemical or biological, to the advantage or disadvantage of other organisms or classes of organisms. In the light of the discussions in this volume, lakes themselves may be regarded in a sense as organisms having innumerable interesting characteristics and entrancing life histories.
Anyone not familiar with lake biology will be impressed with the great variety and abundance of life in lakes and in the sands along their shores. For example, at a distance of 150 centimeters from the shores of certain lakes which were studied there were, on the average, in ten cubic centimeters of sand 4,000,000 bacteria, 8,000 Protozoa, 400 Rotatoria, 40 Copepoda, and 20 Tardigrada. In a lake of moderate dimensions there are probably more individual living organisms than there are vertebrate animals on the whole earth. Naturally this abundant and interesting life in a, complex, varied, ever-varying, and easily accessible environment offers rare opportunities for investigating fundamental problems of the organic world.
F. R. MOULTON