Lakes differ from Rivers.



In lakes the vertical distribution of temperature depending on the season is a very important phenomenon. During summer time a clear thermal stratification can be detected in all deeper lakes. In the upper water layer he tempera temperature is highest, highest, and can be at the at the same level  than the temperature in rivers at the same time.

The temperature in the deeper layer of the lake is, on the contrary,  usually very cold (5 ery cold (5---10 oC) during  the whole summer stratificatification period. This cold layer is a very important part of the lake from the monitoring point of view. Many slight pollution indications can particularly be detected for the first time just in the hypolimnion, us ion, usually in the ally in the very thin water layer nearest to the bottom sediments.

Sedimentation is a very important process in lakes, and has a dominant role in nutrient cycles, and thus also in the eutrophication process. Sedimentation areas must be identified before the implementation of the monitoring programmes

 While some problems originate in a lake itself (such as overfishing), the vast majority of problems originate from activities on the land surrounding a lake. Therefore manangement of a lake means management its draing its drainge basin. The two can not be separated. Unfortunety, it is rare when the boundaries of the basin and political system coincide. In some cases, the origin of a given problem may lie beyond the lakes’s basin such as with long range transport of toxic materials 

Lakes differ f differ from rivers as om rivers as ecosystems in many aspects; • hydrological circumstances, • thermal properties, • production/decomposition relations, • sedimentation rate and sediments, and  n stability of certain phenomena. • Lakes are almost closed systems. Substances once introduced to introduced to the lake are per lake are permanently incorporated in the circulation. • Only a part of them are removed (depending on water exchange rate). • Rivers are open systems, in which  constant downstream transport of substances takes place

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