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若尔盖湿地分布有欧亚大陆最大的高寒冻融泥炭地,具有重要生态碳汇功能。冻融和碳循环过程均会导致地表形变,开展形变监测与分析可为研究冻融和碳循环过程提供重要依据,但当前对该区域地表形变的研究较为缺乏。本文首次以若尔盖高寒冻融泥炭地为研究区域,先期利用2020年1月至2022年12月间的升降轨Sentinel-1 SAR影像及SBAS-InSAR方法获取其地表形变,结合形变分量建模、趋势检验和地表覆盖类型深入探讨其时空特征、变化趋势及泥炭地健康状况。研究表明,该区域垂直向和东西向形变速率分别在-45 mm/a至45 mm/a和-25 mm/a至25 mm/a之间,呈现出沉降与抬升、线性累积与季节性变化以及垂直与水平形变并存的复杂特征,与冻融、碳循环、地温、降雨等因素密切相关,且不同地类形变趋势差异显著,主要与驱动因素的差异相关。本文首次揭示了若尔盖高寒泥炭地的复杂形变特征、变化趋势及影响因素,可为该区域生态功能与脆弱性评估提供科学参考,同时验证了SBAS-InSAR技术在大尺度冻融泥炭地地表形变监测中的有效性。
Abstract: 1. Objective The Zoige Wetland covers the largest alpine permafrost peatland in Eurasia, which has an important ecological carbon sink function. Both the freeze-thaw process of permafrost and the carbon cycle of peatlands can cause surface deformation. Monitoring and analyzing deformation can provide important evidence for studying the freeze-thaw and carbon cycle processes. However, current research on surface deformation in this area is relatively scarce. This paper for the first time takes the Zoige peatland as the study area, and the small baseline subset (SBAS) InSAR was used to monitor its deformation. The spatiotemporal characteristics, evolution trends and driving factors of the deformation were comprehensively studied. The health status of peatlands was evaluated, taking into account the deformation distribution and evolution trend. 2. Method This study obtained 89 ascending and 83 descending Sentinel-1 SAR images from January 2020 to December 2022. The radar line-of-sight (LOS) deformation in the peatland area was extracted by SBAS-InSAR and was verified by comparing with deformation results from the adjacent orbits. The vertical and east-west deformation were obtained by LOS deformation decomposition. The vertical linear cumulative deformation and the seasonal amplitude were extracted by deformation component modeling. At the same time, the historical deformation trend was obtained using the Mann-Kendall trend test and Theil-Sen estimation methods, and the future deformation trend was estimated based on the Hurst index. The spatial and temporal characteristics, change trends of the deformations and health status of the peatland were explored in depth by combining diverse information such as land cover type, surface temperature, and precipitation. 3. Result The correlation coefficient of the LOS velocity of the overlapping areas between adjacent orbits reaches 0.74, and the root mean square error is ±0.55 mm/a. The vertical and east-west velocity in the study area range from -45 mm/a to 45 mm/a and from -25 mm/a to 25 mm/a, respectively. The vertical deformation is mainly distributed in the peat area being concentrated around the wetlands and water bodies, and the western high-altitude area. The non-peat area in the northwest has relatively obvious eastward deformation affected by elevation and aspect. Seasonal deformation is mostly concentrated in the peat areas, especially around the Cuorewajian Lake and the Manrima Township, with the maximum amplitude of 16.9 mm. The trend test results demonstrate that the areas with significant uplift and subsidence trends account for 51.95% and 26.10% of the total area respectively, while the remaining areas with uplift and subsidence trends account for 8.38% and 5.88% respectively. 75.72% of the area may show anti-continuity trend in the future, and 24.28% of the area may maintain the current trend. 4. Conclusion The deformation of the Zoige peatland exhibits complex characteristics and distribution patterns of subsidence and uplift, linear accumulation and seasonal changes, as well as vertical and horizontal components coexisting. This is mainly related to factors such as freeze-thaw, carbon cycle, land surface temperature, and precipitation. Moreover, the deformation trends of different land types vary significantly, mainly due to the differences in driving factors. Overall, the uplift area of the Zoige peatland is larger than the subsidence area, indicating a good carbon sink function. However, local significant subsidence phenomena occur in areas such as the Cuorewajian Lake surroundings, and are accompanied by a high Hurst index, indicating a significant subsidence persistence. Thus, the peatland in these areas may face up to degradation risks. This study first reveals the complex deformation characteristics, change trends, and influencing factors of the alpine permafrost peatland in Zoige, providing scientific reference for the assessment of ecological functions and vulnerability in this region. It verifies the effectiveness of the SBAS-InSAR technology in monitoring the surface deformation of large-scale permafrost peatlands.
