Inland waters: spotlight on lakes and rivers
The interaction of temperatures and weather extremes over the course of the seasons influences the ecological relationships in inland waters in a complex way. Climate change is having a correspondingly diverse effect here.
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Lakes not only have a high recreational value, they also secure part of the drinking water supply and thus our livelihood. Inland waters also play a major role in climate change: taken together, they accumulate more carbon in their sediments than the bottom of all the oceans.
Over the past few decades, global warming has already significantly altered lakes and rivers. Because the temperature there directly or indirectly influences all essential processes, whether physicochemical or biological. On a global average, their summer surface temperatures have risen by about a third of a degree Celsius per decade over the past 30 to 40 years. At the same time, in the temperate zone of the northern hemisphere, the length of time that lakes are covered by ice has decreased by more than two weeks. For example, by the end of the century, conditions at the Müggelsee in Berlin will probably be as if they had been geographically shifted south by about 800 kilometers, i.e. as in northern Italy today.
Climate change has a particularly clear effect on the thermal stratification of lakes. In spring, surface water warms up faster than lower-lying areas. This creates a barrier for the exchange of oxygen and nutrients between the top and bottom. The condition generally persists throughout the summer and now begins two to three weeks earlier in the year due to milder winters and higher spring temperatures in temperate zone lakes. It also lasts longer in autumn …