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Freshwater ecosystems - Lentic Aim Running waters (rivers) and standing waters (lakes) and its applied aspects, specifically pollution. Properties of water that influence the environment. Composition of the hydrosphere o 97.2% seawater o 2.24% glaciers o 0.009% STANDING WATER (LENTIC) o 0.0001% RUNNING WATER (LOTIC) Most freshwater locked up in glaciers. Water security and conflicts arise because there is not much fresh water around. Within freshwaters, there are a number of forms. There are lakes and wetlands (lentic) and rivers and estuaries (lotic), although estuaries can be lumped under marine as many of the species present are of marine origin. Why are freshwaters important?
Irrigation, drinking water, transport (including of natural resources), and disposal of wastes. Some can be dammed and used for drinking or irrigation. The lake environment Physical properties: Depends on the properties of water (thermal conductivity, thermal capacity and surface tension and viscosity); the effect of abiotic factors such as light, wind, temperature; also seasonal changes which include lake stratification and mixing. Chemical environment: Typical lake nutrients include nitrogen, phosphorous and silicon. Contains many inorganic ions and many dissolved gases including oxygen, nitrogen and carbon dioxide. Biological communities: Can include biofilm and pelagic communities. Diversity of organisms, and there dynamic interactions. Properties of water Thermal conductivity - low, heat only passed on slowly between different water masses unless there is physical mixing. Why the sea is cold on a hot day. Thermal capacity - high - lots of energy needed to raise the temperature by a degree Surface tension and viscosity - high so animals may live on the surface film. Also slows down settlement through the water column. Transparency - light absorbed exponentially. Particulates in the water column may reduce transparency. Solubility of dissolved oxygen - low and temperature-dependant. (less than 0.001% by mass). Thus concentration relatively low and can be limited. Can limit biota - some fish are intolerant of low oxygen whilst some are tolerant (salmon and trout require high levels of oxygen and wont be dominant in lakes with high temperatures).
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