ABSTRACT
An ecosystem—a set of organisms living in a delimited area as well as the resources needed to keep them alive—is characterized by a cycle of biosynthesis and biodegradation of organic matter. The force of the moving water simultaneously erodes the materials of the watershed—resources necessary for the functioning of the ecosystem, mineral salts, and necromass—and drags living organisms with it. The horizontal functioning of lotie ecosystems is based primarily on the utilization of organic matter transported by detritivorous organisms that feed on it, on the fungi and bacteria that degrade and oxidize it. In oceanic and lacustrine ecosystems, exchanges of oxygen and carbon dioxide at the water-atmosphere interface are under the dominant control of photosynthesis and the respiration of organisms. This mode of control is secondary in running waters, where turbulence phenomena are dominant and more easily balance the gaseous exchanges between water and atmosphere.
