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"The concentrations of radon and methane in the water of the subsoil are highly variable, which means that it is necessary to work with a large number of samples to be able to determine their magnitude with good precision", says Valentí Rodellas, a member of the ICTA-UAB research team. "The soils of these rich, dense regions, which have a great capacity to retain water, make it even more difficult to obtain a sufficient volume of water to carry out the analyses. We also had to transport tens of kilos of material in our backpacks over relatively long distances to reach the reservoirs, as there was no motorised transport",
he adds.
More greenhouse gas emissions in summer
The study reveals that the inflow of methane gas through groundwater into the lakes is more intense in the summer than in autumn due to the greater abundance of water circulating in the subsoil (melting, rain, etc.). The higher temperatures in the summer also favour the production of methane in the subsoil and, therefore, enrich the gas content of the groundwater that goes to the lakes.
"Climate change and accelerated permafrost melting will increase the amount of greenhouse gases that can be transported to the lakes through groundwater. The increase in precipitation —up to 40% in the Arctic over the next decade— will also increase the flow of groundwater and, therefore, the discharge of methane into the lakes", says researcher Carolina Olid.
A greater emission of greenhouse gases into the atmosphere is not the only effect caused by the melting of permafrost. "Permafrost water contains high concentrations not only of greenhouse gases such as carbon dioxide (CO2) or methane (CH4), but also of other compounds such as nutrients, and pollutants (mercury, etc.). The arrival of these compounds in the lakes generates harmful impacts on the natural environment and the organisms that live in lake ecosystems, as well as in terrestrial systems (bogs, etc.)", says Gerard Rocher-Ros, postdoctoral researcher at Umeå University.
"These are effects with implications for the entire aquatic trophic chain of both the lake itself and the network of interconnected rivers and streams, which have an impact on the ecosystem services provided by natural resources to society”, adds Carolina Olid.
Improving climate change prediction in the future
It is still difficult to determine those areas of the planet where the process of permafrost melting will be more pronounced or faster. In some areas, some lakes will dry up because the water will flow out through the drains or new channels formed by the melting. In other cases, the lakes will expand their margins as the melting progresses —a process known as thermokarst— and new lakes will emerge in relief depressions.
In this scenario of climate uncertainty, the introduction of groundwater discharge into climate models will improve predictions of future methane emissions from lakes.
"This will allow us to assess the real role of lakes in the carbon cycle and whether they really function as sources or as potential reservoirs of greenhouse gases. This information is key to developing appropriate conservation policies to mitigate climate change", concludes lecturer Carolina Olid.
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