| Summary: | This review article deals with the question of how biogeochemical processes influence the physics of lakes. An important phenomenon is the steady transport of chemicals by settling particles to the deep waters of lakes and oceans accompanied by the production of negative buoyancy (gravitation-induced stability production). Meromixis develops if the vertical mixing resulting from the input of kinetic energy is not sufficient to overcome this stability. This is often the case in eutrophic lakes, exemplified here by Lake Baldegg (Switzerland), as a result of intense nutrient cycling. A second class of phenomenon is related to river inflow. As shown here for Lake Baikal and Lake Lucerne, river inflow may be important for deep-water renewal, especially during peak discharge, when suspended particles increase the bulk density of the river water. In addition, if the drainage basins of inflowing rivers have different geochemical characteristics, significant density gradients may be established between basins, possibly driving inter-basin exchange over sills or through narrows and sea straits (e.g. Black Sea, Mediterranean, North Atlantic). Situations also exist in which organisms influence the physics of their environment directly, some examples of this being the input of turbulent kinetic energy by swimming fish, the intensification of vertical density stratification resulting from light absorption by large concentrations of phytoplankton, and the vertical convection induced by sinking bacteria at the oxic/anoxic interface in a meromictic lake.
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