干旱区生态环境知识资源中心

Shallowness and tropicality primarily relate to physical aspects of environmental regulation. These concern water input and output, with correlates associated with water level and salinity; energy balance and beat distribution, with correlates of temperature and density stratification; and largely wind-driven water movements, with consequences in chemical and biological distributions. Shallowness in a water-column affects the quantitative relationship between many stock quantities and flux rates per unit surface area. Evaporative loss of water is one familiar example; sensitivity to surface energy exchanges provides others. Somewhat different are processes that depend upon transmission with depth. Here light penetration, convective penetration and wind-generated turbulence with flow-depth relations are illustrative. Tropicality further influences by climatic factors, especially of solar radiation and rainfall. Energy balance tends to yield year-long elevated water temperature at all depths, but at a level dependent upon altitude. The magnitude and seasonal periodicity of water input is widely dependent upon the inter-tropical convergence zone in atmospheric circulation. Over the arid and semi-arid tropics, the lakes may lie in closed drainage basins and be influenced by evaporative concentration with salinization. Shallow takes of tropical Africa are used to illustrate these varied environmental constraints and some of their biological consequences.