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Lakes under climate change

Lake Stechlin freezes over for fewer days in the year. © M. Feierabend
Lake Stechlin freezes over for fewer days in the year. © M. Feierabend

Increased temperatures, decreased rain, altered wind conditions and more frequent extreme events: The exact consequences of climate change on ecosystems are the subject of numerous research projects around the world. Scientists from IGB are studying the effects of climate change on a clear water lake in the northeast of Germany, Lake Stechlin. They expect their findings to yield insights on the consequences for lakes in general. The researchers believe that climate change influences many properties of a lake: thermal stratification, nutrient availability, material turnover rates, diversity and composition of organisms, and concentration of oxygen in the deep water to name a few examples.

Climate change will certainly not spare Lake Stechlin. Over the last 50 years, the surface water has warmed by more than 1.5 °C. This can be seen from long-term measurements. The durations of the thermal stratification phases is also changing: Given warmer winter temperatures, summer stratification now sets in earlier than in previous decades. The scientists have also noted that Lake Stechlin is remaining ice-covered for fewer days in the year. According to model calculations, this trend will continue to amplify until the end of the 21st century, whereupon the winter stratification phase will disappear.


One particularly important factor that defines the character of lakes is their oxygen content. As water temperature increases, the solubility of this gas drops sharply – contrary to what we are familiar with for salt or sugar. At the same time, warmer temperatures accelerate the metabolism of the organisms in the lake resulting in oxygen depletion in the deep water. If algae create more biomass on top of this, then a greater amount of organic material will be available for degradation processes that will use up the oxygen even further. If extreme cases of oxygen-free conditions arise in the depths during the summer stratification phase, then the composition of organisms there will change strikingly. Fish and invertebrates will lose their habitat entirely, and even the composition of microorganisms will shift dramatically.