As covered in Lecture 17, Lake Ecosystems go through cycles throughout the year depending on their location. Around the great lakes, the summer results in thermal stratification, which prevents mixing between the epilimnion and hypolimnion. Stratification essentially cuts off the nutrient flows between these layers, therefore, during the summer months, algae and other organisms use up nutrients in the epilimnion (upper layer). Algae and other microorganisms cannot access nutrients trapped in the hypolimnion until the fall.
Once summer passes, wind causes the mixing of layers and the lake essentially becomes one layer. In the winter, ice may float over the surface while the bottom remains unfrozen. As the ice melts in the spring, winds cause layer mixing bringing nutrients up from sediments and oxygen to deeper.
According to Dr. Ankur R Desai of University of Wisconsin-Madison in Nature Geoscience, decreased ice coverage in the winter seem to cause stronger winds in the summer. Less ice means a decreased albedo for Lake Superior, which warms the lake faster as the seasons change. The study found an increase in air and surface water temperatures and a decrease in temperature gradient between air and water. Reductions in the temperature gradient causes a destabilization in the atmospheric surface layer thus increase wind speeds over Lake Superior 5% per decade.
Consequentially, faster winds create stronger currents causing the epilimnion to become shallower and longer summer stratification. The algae and other organisms will have to survive longer in the without mixing. The study concludes “climate change will profoundly affect the biogeochemical cycles of large lakes, the mesoscale atmospheric circulation at lake-land boundaries and the transport of airborne pollutants in regions that are rich in lakes.”