Seasonal variability of environmental processes in lakes reveals sensitivity to climate change

A new study has shown how climate change could impact the ecosystems of the planet’s largest lakes by revealing different levels at which their water layers mix throughout the seasons. As climates warm, changes in this process during the winter months could affect oxygen levels and other vital natural environmental systems.

Lake Geneva – Credit: Hugo Ulloa

The mixing, caused by the natural turbulence of deep water bodies, controls the movement of heat, oxygen, nutrients and pollutants between the different layers and therefore plays a major role in how ecosystems develop. adapt to environmental forces. In lakes and other inland water bodies, where tidal currents are weak, the energy for mixing is provided by the wind blowing at the surface, which feeds the currents in the water body.

For this new study, an international study team used the 100 square meter LéXPLORE research platform, floating in Lake Geneva, to continuously measure wind speed, lake current speed and temperature, at inside the body of water and near the sediments, for a whole seasonal cycle.

The LéXPLORE platform. Credit: Camille Minaudo

The results, published in the journal Nature Communications Earth & Environment, showed that energy pathways are seasonally controlled through changes in wind intensity and different density layers in the water. In summer, the mixture is weaker and limited within the body of water; it is the result of lighter winds and the stability provided by the heat of the sun which retains wind energy in the upper layers of water.

In the windiest winter season, the mixing was three times stronger and most of it occurred in the lower boundary layers above the sediments of the lake.

The study was led by Dr Bieito Fernández Castro, a researcher at the University of Southampton who began the study while working at the Federal Polytechnic in Lausanne, Switzerland.

Dr Fernández Castro said: “Inland freshwater bodies like lakes are an important resource for the communities that live around them; they can provide clean water, food, generate energy and provide opportunities for recreation. However, this close interaction also means that they face threats from human factors such as global warming. “

Previous studies of mixing in lakes have faced technical and operational challenges of measuring turbulence in the field with sufficient temporal coverage and resolution. It is therefore the first and the first time that such variability has been recorded, revealing the risk to the natural mixing process of rising global temperatures.

“This work illustrates the importance of monitoring lake currents and turbulence over long periods of time to understand their response to climate change. Our results show that warmer climates during the winter months could strongly affect turbulent mixing patterns, especially in the lower layers. This in turn could have a significant effect on a lake’s oxygen levels, the resuspension of sediment – where particles on the bed are redistributed into the lake’s water layers – and other environmental processes. vital, ”concluded Dr Fernández Castro.

The team also says that many questions remain open for further research, particularly around the variability of this near-shore process versus open water and the near-surface mixing response to strong wind events. and episodic.

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