GEOGRAPHY

Arctic permafrost has lost 35,000 lakes in the last 35 years


Climate change has become a global issue affecting human life. In recent years, significant warming in the Arctic has led to a large-scale thawing of permafrost, affecting fragile Arctic ecosystems and causing problems such as lake drainage, posing challenges to the survival of indigenous peoples and wildlife.

Focusing on the field of Arctic ecological environment, the joint polar remote sensing team of Sun Yat-sen University and Shandong Normal University used satellite remote sensing technology to monitor more than 35,000 lake drainage events in the Arctic permafrost area in the past 35 years, released an Arctic drainage lake dataset containing high-precision spatio-temporal information, and quantitatively analyzed the dynamics of lake basin vegetation after drainage, revealing the key environmental factors affecting lake drainage and lake basin vegetation growth. On November 15, the results were published in Nature Communications.

“This study expands the understanding of the dynamics of Arctic lakes and the phenomenon of Arctic greening, which is of great significance for predicting future changes in Arctic lakes and provides a scientific basis for formulating targeted strategies for the protection of the Arctic ecological environment.” Cheng Xiao, the corresponding author of the paper and director of the Polar Research Center of Sun Yat-sen University, told China Science Daily.

Drainage lakes in the Arctic permafrost region with drainage channels visible in the lower left corner. (Photo by Dave Swanson)

After the lake is drained, the vegetation in the lake basin grows rapidly (Photo by Sergey Loiko)

Uncover the events behind the “trend”.

Lakes are an important part of the Arctic ecosystem, providing water to remote Arctic communities, providing habitat for wildlife, and playing an important role in the carbon cycle and regional energy balance. Satellite observations show that the surface water area of the Arctic region has shown a trend of drying up over the past 20 years, which contradicts the simulation results of existing theoretical models. In the existing studies, the understanding of Arctic lake drainage events is still at the level of phenomenon analysis, and there are some problems, such as limited spatial scope, short time span, lack of continuous observation and quantitative analysis, etc., resulting in the spatiotemporal law and influencing factors of lake drainage events are still unclear.

“As a result of Arctic warming, solid ice wedges in permafrost melt into liquid water to replenish surface water systems. Therefore, it is theoretically accepted that the Arctic region will become more and more humid in the future. But in fact, in the Arctic coastal lowlands, where lakes are dense and the soil is rich in subsurface ice, the surface subsidence associated with melting ice wedges can cause lake shores to capsize and drainage channels to form, causing lakes to disappear in weeks or even days. This process is known as the lake drainage event that is unique to permafrost areas. Chen Yating, the first author of the paper and associate professor of the School of Geography and Environment of Shandong Normal University, said.

In order to deeply explore the lake drainage events behind the Arctic drying up trend, the team used multi-source satellite remote sensing data products and advanced time series segmentation and change detection algorithms to generate the most widely distributed, longest-time-spanned and most accurate lake drainage event dataset, which provides detailed basic data support for understanding the driving factors behind the changes of Arctic lakes.

“Unlike previous studies, we used a lake object-based rather than image-based analysis method, which allowed us to identify 35,337 lake drainage events from about 5.83 million lakes in the entire Arctic permafrost region, and to achieve lake-scale drainage probability analysis and accurate detection of drainage years, so as to show the differences in drainage probability of Arctic lakes of different sizes, different landform types and different origins.” Dr. Liu Aobo, co-corresponding author of the paper and a young teacher at the School of Geography and Environment of Shandong Normal University, said.

Unraveling the rise of the “Arctic Oasis”. 

After the lake is drained, Arctic vegetation begins to colonize in the drained lake basin, gradually transforming the landscape from bare lake basin sediments to tundra. Because the drainage basin is wetter than the surrounding area and the soil is rich in nutrients, vegetation grows rapidly in the drainage basin, rapidly reaches the greenness level of the surrounding vegetation, and may succeed in the direction of more productive communities.

“We first discovered this phenomenon in a case study in 2021, which aroused widespread interest in the academic community after its publication, but considering the spatial and temporal heterogeneity of vegetation dynamics, we have not been able to draw generalizable conclusions.” “Based on the monitoring of lake drainage events in the entire Arctic permafrost region, we found that it is a common phenomenon that the vegetation in the drainage lake basin is greener than the surrounding area,” Chen said.

Drainage lake basins are hotspots for the Arctic to turn green, increasing the diversity of ecosystems. The drainage lake basin forms a mosaic of habitats at different successional stages, which promotes interspecies competition in tundra vegetation and has a profound impact on the vegetation composition, abundance and distribution of tundra ecosystem.

By tracking the vegetation dynamics of the drainage lake basins, the study revealed the spatial variability of the vegetation dynamics of the drainage lake basins under different environmental conditions, and found that the vegetation growth status was better in the hot melt lakes and the arctic lakes with large areas and high drainage ratios.

In addition, the study quantified the influence of environmental factors on predicting vegetation dynamics in the drainage lake basin, and found that temperature and flooding were key environmental constraints. These findings will help to manage the drainage lake basin as an ecological hotspot mosaic and facilitate future efforts to conserve Arctic biodiversity.

More far-reaching implications

In the future, with the continuous warming of the Arctic, the thickness of the active layer in the permafrost area will gradually deepen, and the permafrost discontinuity will increase, which is expected to lead to more frequent lake drainage events. Drainage events can reduce the lake’s water storage capacity and affect local hydrological conditions. The drainage of large lakes and lake groups can cause secondary disasters such as floods, and there are periodic peaks due to snowmelt peaks in spring and summer. Such hydrological events can adversely affect infrastructure such as roads and pipelines in the Arctic.

As more and more lakes are drained, access to clean fresh water is likely to become more difficult for many Arctic communities and indigenous peoples. Species that depend on lake habitats, such as migratory birds and aquatic life, are also threatened. For example, on St. Lawrence Island, near Alaska, nearly one-quarter of the lake has been observed to drain since 2018, and the surrounding sea ice cover has reached an all-time low during the same period, indicating that local climate conditions may have reached a tipping point.

Lake drainage affects regional hydrology and ecology, and also has complex feedback effects on carbon balance. When the lake is drained, the otherwise submerged soil organic matter is exposed to the air, reducing methane emissions from anaerobic respiration by microorganisms on the lake floor and providing space for tundra vegetation to grow. In addition to the direct carbon sequestration benefits, vegetation growth brings a range of environmental benefits, including enhanced permafrost stability, preventing soil erosion, improving water quality, creating habitats for wildlife, increasing biodiversity, and supporting indigenous livestock activities.

“In the future, we will expand the application of satellite remote sensing technology in polar regions, such as using China’s self-developed terrestrial ecosystem carbon monitoring satellites, combined with our lake drainage event dataset, to monitor carbon source and sink changes in key drainage lake basins. At the same time, high-resolution drone technology is used to strengthen monitoring and deeply explore the drainage mechanism of different types of lakes. We will further consider how to combine existing knowledge with future projections provided by Earth system models to explore lake changes and vegetation dynamics in the Arctic under various future scenarios, and to assess their impact on Arctic greenhouse gas emissions and international carbon neutrality strategies. Cheng Xiao said. (Source: Cui Xueqin, China Science News)

Related Paper Information:https://doi.org/10.1038/s41467-023-43207-0



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