Aapa mires are waterlogged northern peatland ecosystems characterized by a patterned surface structure where water-filled depressions (‘flarks’) alternate with drier hummock strings. As one of the EU Habitat Directive priority habitats, aapa mires are important for biodiversity and carbon cycling, harbouring several red-listed species and supporting unique species communities. Due to their sensitivity to hydrological disturbances, reliable, up-to-date and systematic information on the hydrological condition and responses of mires is crucial and required for multiple purposes ranging from carbon exchange modelling to EU Habitats Directive reporting and conservation and ecosystem restoration planning. Here, we demonstrate the usability of Sentinel-2 satellite data in a semi-automatic cloud-based approach to retrieve large-scale information on aapa mire hydrological variability. Two satellite-derived metrics, soil moisture index and the extent of water-saturated surfaces based on pixel-wise classification, are used to quantify monthly and interannual wetness variation between 2017 and 2020 across Natura 2000 aapa mires in Finland, including responses to the extreme drought of 2018. The results revealed high temporal variability in wetness, particularly in the southern parts of the aapa mire zone and generally in the late summer months interannually. Observations from the drought summer showed that one third of usually year-round wet flark surfaces may be exposed to drying during climatic extremes. Responses varied between sites and regions, implicating the significance of environmental factors for drought resistance: some sites maintained high levels of moisture, whereas others lost wet surfaces completely. Our study provides the first comprehensive national-level representation of seasonal and interannual wetness variability and drought-sensitivity of pristine aapa mire sites. The approach and methods used here can be directly upscaled outside protected areas and to other EU countries. Thus, they provide a means for harmonized, systematic large-scale monitoring of this priority habitat, as well as valuable information for other applications supporting peatland conservation and research.

中文翻译：

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使用 Sentinel-2 量化 aapa 泥沼的湿度变化：改善对欧盟优先栖息地的监测

Aapa 泥炭沼泽是北部浸水的泥炭地生态系统，其特征是具有图案化的表面结构，其中充满水的洼地（“flarks”）与干燥的山丘串交替出现。作为欧盟人居指令的优先栖息地之一，aapa 沼泽对于生物多样性和碳循环非常重要，栖息着多种红色名录物种并支持独特的物种群落。由于泥沼对水文扰动的敏感性，有关泥沼水文状况和响应的可靠、最新和系统的信息至关重要，并且需要用于从碳交换模型到欧盟生境指令报告以及保护和生态系统恢复规划等多种目的。这里，我们展示了 Sentinel-2 卫星数据在半自动基于云的方法中的可用性，以检索有关 aapa 泥沼水文变化的大规模信息。土壤湿度指数和基于像素分类的水饱和表面范围这两个卫星衍生指标用于量化 2017 年至 2020 年芬兰 Natura 2000 aapa 沼泽的月度和年际湿度变化，包括对极端情况的响应2018 年干旱。结果显示，湿度随时间变化很大，特别是在 aapa 泥沼区的南部地区，并且通常在夏末的几个月内存在年际差异。对干旱夏季的观察表明，在极端气候期间，通常全年潮湿的地面表面有三分之一可能会变得干燥。不同地点和地区的反应各不相同，暗示了环境因素对于抗旱的重要性：一些地点保持了高水平的湿度，而另一些地点则完全失去了潮湿的表面。我们的研究首次在国家层面全面展示了原始 aapa 沼泽地的季节性和年际湿度变化以及干旱敏感性。这里使用的途径和方法可以直接推广到保护区之外和其他欧盟国家。因此，它们提供了一种对这一优先栖息地进行协调、系统的大规模监测的手段，并为支持泥炭地保护和研究的其他应用提供了宝贵的信息。我们的研究首次在国家层面全面展示了原始 aapa 沼泽地的季节性和年际湿度变化以及干旱敏感性。这里使用的途径和方法可以直接推广到保护区之外和其他欧盟国家。因此，它们提供了一种对这一优先栖息地进行协调、系统的大规模监测的手段，并为支持泥炭地保护和研究的其他应用提供了宝贵的信息。我们的研究首次在国家层面全面展示了原始 aapa 沼泽地的季节性和年际湿度变化以及干旱敏感性。这里使用的途径和方法可以直接推广到保护区之外和其他欧盟国家。因此，它们提供了一种对这一优先栖息地进行协调、系统的大规模监测的手段，并为支持泥炭地保护和研究的其他应用提供了宝贵的信息。