Freshwater ecosystems

Abstract

Freshwater ecosystems are associated with the lakes and channels through which precipitation is returned to the ocean as part of the hydrologie cycle. The transition to an aquatic environment occurs where water depth or strong currents prevent the growth and development of terrestrial organisms. Plants and animals have adapted to these conditions in various ways and the structure of aquatic communities reflects the physical and chemical properties of the waterbodies in which they grow. Lakes and ponds function essentially as closed systems, even though water enters and leaves these temporary storage basins in various ways. Water movement is slow and turnover times typically range from 1 to 100 years, depending on volume, depth and rate of discharge (Wetzel, 1975). There is a tendency for materials to accumulate in the still water and consequently ponds and lakes undergo a natural ageing process. The rate of change depends on hydrologie conditions and the size and shape of the basin but it is generally assumed that the open water habitat is eventually lost.