The Ecosystem of the largest freshwater lakes in the world changes dramatically
Over the largest of the Great lakes — Upper began to blow strong winds. So Yes, that started to change the lake ecosystem. The cause of the phenomenon and the consequences to find out, scientists from Wisconsin.
In canadian-American shore of lake superior, the largest area of freshwater lake in the world, over the last 20 years have seen major changes. Professor of Ankur Desai (Desai Ankur) from the University of Wisconsin and his colleagues came to an unexpected conclusion: the increase in the temperature of atmospheric air in the summer has led to the fact that the speed of the winds blowing over the lake has increased. According to scientists, for the same reason, the increased speed and currents. Naturally, such changes could not but affect the inhabitants of the water.
While in sight of limnologen (Ostrovidov) managed to get only the phytoplankton. The scientists conducted their research since 1985. Based on data collected using three hydrological buoys and satellite imagery, Professor Desai and his colleagues have figured out what is going on with the Top.
The lake warms up…
According to scientists, the temperature in the surface layers of the lake during the summer period increased at a rate of 1.2°C in one decade. And the water heats up 15% faster than the air over the lake. “The fact that the temperature regime of a lake depends largely on the amount of ice and the time of its melting. That is, the earlier occurs the melting of the ice on the lake, the faster heats the water itself,” the authors explain.
The wind increases…
The difference in the growth temperature leads to a stronger wind. The fact that the wind speed on any body of water is determined by the interaction between the surface water and the lower layers of the atmosphere. The greater the difference between air and water temperature, the more stable the atmosphere is formed with a predominance of weak winds. When the difference decreases, the atmosphere becomes hectic – there begins to form many vortices. Professor Desai has calculated that the wind speed over the lake is increased by 5% per decade, and the speed of currents, affected by all these changes, increases by 10% per decade.
How is phytoplankton?
Theoretically, if the speed of the currents increases, then the mixing of layers of water of different temperature and different properties should happen faster, and these conditions are just very favorable for phytoplankton. This means that it should grow. But the research by Professor Desai show that this is not happening. The content of chlorophyll in the lake (according to this index one can judge about the well-being and the amount of phytoplankton) is reduced.
Professor Desai and his colleagues believe that the heating of the surface of the water, increasing speed of wind and currents has led to the fact that the period of temperature stratification when warm layers near the surface and colder at depth clearly separated from each other, was longer than a few days. So, the water is no longer mixed and phytoplankton are created for adverse conditions.
Another trouble that has befallen lake superior, – the diffusion of pollutants. Because with increasing wind speed, the pollutants easily and quickly moved above the lake.
In the future, the researchers plan to see what happens to the carbon cycle in the lake and how the phytoplankton, if all of these changes will continue.
Article with the results of this study can be found in the latest issue of the journal Nature Geoscience.