Seasonal variability in lakes' environmental processes reveal
susceptibility to climate change

Date:
October 12, 2021
Source:
University of Southampton
Summary:
A new study has shown how climate change could impact the ecosystems
of the planet's largest lakes by revealing varying levels at which
their water layers are mixed together through the seasons. Natural
mixing in lakes is much stronger during winter months compared to
summer months due to differences in wind strengths.



FULL STORY ==========================================================================
A new study has shown how climate change could impact the ecosystems of
the planet's largest lakes by revealing varying levels at which their
water layers are mixed together through the seasons.


========================================================================== Mixing, caused by natural turbulence of deep water bodies, controls
the movement of heat, oxygen, nutrients and pollutants between different
layers and therefore plays a major role in shaping how ecosystems adapt to environmental forces. In lakes and other inland waterbodies, where tidal currents are weak, the energy required for mixing is supplied by wind
blowing at the surface, which energises currents within the waterbody.

For this new study, an international study team used the 100-square-metre research platform Le'XPLORE, floating in Lake Geneva, to continuously
measure wind speed, lake current velocities and temperature, in the
interior of the water body and near the sediment, for an entire seasonal
cycle.

The findings, publishing the journal NatureCommunications Earth &
Environment, showed that the energy pathways are controlled by seasonality though changes in the intensity of winds and different layers of density
within the water. In summer, mixing is weaker and restricted to the
interior of the waterbody; this is the result of lighter winds and the stability brought about by heat from the sun which retains the wind
energy in the upper water layers.

In the windier winter season, mixing was three times stronger and most
of it took place in the bottom boundary layers over the lake sediments.

The study was led by Dr Bieito Ferna'ndez Castro, a research fellow
at the University of Southampton who began the study whilst working at
E'cole Polytechnique Fe'de'rale de Lausanne, Switzerland.

Dr Ferna'ndez Castro said: "Inland freshwater bodies like lakes are an important resource for the communities living around them; they can
provide drinking water, food, generate energy and offer recreational opportunities.

However this close interaction also means they face threats from human
factors such as climate warming." Previous studies on mixing in lakes
have faced technical and operational challenges of measuring turbulence
in the field with sufficient temporal coverage and resolution. This is therefore the first this is 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 in the winter months could strongly affect the patterns of turbulent mixing, particularly in
the lowest layers. This could in turn have a significant effect on a
lake's oxygen levels, resuspension of sediments -- where particles on
the bed are redistributed within the lake's water layers -- and other
vital environmental processes," Dr Ferna'ndez Castro concluded.

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

========================================================================== Story Source: Materials provided by University_of_Southampton. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Bieito Ferna'ndez Castro, Damien Bouffard, Cary Troy, Hugo N. Ulloa,
Sebastiano Piccolroaz, Oscar Sepu'lveda Steiner, Hannah
E. Chmiel, Lucas Serra Moncadas, Se'bastien Lavanchy, Alfred
Wu"est. Seasonality modulates wind-driven mixing pathways in a
large lake. Communications Earth & Environment, 2021; 2 (1) DOI:
10.1038/s43247-021-00288-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012130716.htm

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