Decoupled Aquatic Greening and Water-Area Dynamics in Northeast Siberian Arctic Thermokarst Lakes from 2000 to 2025

Thermokarst lakes are sensitive components of Arctic permafrost landscapes and important methane sources, yet aquatic vegetation change is rarely examined together with lake water dynamics. We used Landsat observations to quantify water area, aquatic vegetation occurrence frequency, and maximum vegetation extent for 32,439 lakes in Northeast Siberia from 2000 to 2025. Long-term trends, rapid events, event-centered trajectories, and water–vegetation coupling were analyzed at regional and individual-lake scales, while a same-lake case–control design examined climate anomalies associated with rapid vegetation increases. Regional lake water area showed a net increase of only 0.05% between the 2000–2004 and 2021–2025 mean periods because gains in small lakes were offset by losses in large lakes. Over the same two periods, maximum aquatic vegetation extent increased by 172.5%, and 47.4% of lakes showed a significant increase. Stable water area combined with increasing vegetation extent in 39.9% of all lakes, indicating substantial long-term decoupling. Rapid lake contraction was followed by gradual vegetation increases, whereas rapid vegetation increases generally occurred without systematic lake-area change. Event years were more often associated with a positive growing-season water balance and reduced May–July snowmelt, although these relationships varied among years. Aquatic greening therefore represents substantial ecological reorganization within Arctic lake basins that is only partly captured by conventional surface water monitoring.