ABSTRACT
The question of the circulation of organic matter in Lake Leman is more complex than that of the circulation of mineral matter. Only a small part leaves the lake with the effluent. Organic matter comes from the rain, the catchment area and the atmosphere. Dissolved organic matter, cadavers or dead remains, living animals and plants all have different destinies, are embodied in different forms and undergo transmutations and metamorphoses. Lake plants obtain nourishment by absorbing mineral matter dissolved in the ambient water. They might be eaten by a herbivore or die and decay. They are the basis of the food supply for animals. After being absorbed in the plant and the animal, organic matter returns to the state of a solution. The cycle is completed. Why then is there not an over-abundance of organic matter? Because of animals fishing and animals fished, debris thrown onto the lake shore, transport by the effluent and discharge into the atmosphere in the form of gas. Lake water is thus purer than that of the various lake affluents.
