Nature Geoscience: 通过量化水库消落带碳排放颠覆全球水库碳收支
水库消落带-由于水位波动致使沉积物暴露在大气中-是CO2排放的热点区域。由于缺乏全球水库消落带面积数据，致使水库碳收支无法得到准确评估。1985-2015年6794个水库的卫星观测数据表明，全球水库约有15%的面积为消落带。在靠近热带的水库中，消落带的暴露最为明显，并且显示出对气候（降水、温度）和人为（用水）驱动因素的复杂依赖性。本研究根据已发布的区域排放率将CO2和CH4的排放分配至水库水面及消落带，重新评估了全球水库的碳排放。结果显示消落带CO2的排放量为26.2（15-40）TgCO2-C yr-1，且全球水库CO2排放量增加了53% [60.3 (43.2-79.5)] TgCO2-C yr-1。考虑消落带的面积时，碳排放与沉积物中碳埋藏比为2.02（1.04-4.26）。这表明水库排放的碳多于水库埋藏的碳，对目前水库是净碳汇的理解形成挑战。因此，对于水库消落带的考虑推翻了关于全球水库在碳循环中为碳汇的理念。
Reservoir drawdown areas—where sediment is exposed to the atmosphere due to water-level fluctuations—are hotspots for carbon dioxide (CO2) emissions. However, the global extent of drawdown areas is unknown, precluding an accurate assessment of the carbon budget of reservoirs. Here we show, on the basis of satellite observations of 6,794 reservoirs between 1985 and 2015, that 15% of the global reservoir area was dry. Exposure of drawdown areas was most pronounced in reservoirs close to the tropics and shows a complex dependence on climatic (precipitation, temperature) and anthropogenic (water use) drivers. We re-assessed the global carbon emissions from reservoirs by apportioning CO2 and methane emissions to water surfaces and drawdown areas using published areal emission rates. The new estimate assigns 26.2 (15–40) (95% confidence interval) TgCO2-C yr−1 to drawdown areas, and increases current global CO2 emissions from reservoirs by 53% (60.3 (43.2–79.5) TgCO2-C yr−1). Taking into account drawdown areas, the ratio between carbon emissions and carbon burial in sediments is 2.02 (1.04–4.26). This suggests that reservoirs emit more carbon than they bury, challenging the current understanding that reservoirs are net carbon sinks. Thus, consideration of drawdown areas overturns our conception of the role of reservoirs in the carbon cycle.
Keller, P.S., Marcé, R., Obrador, B. et al. Global carbon budget of reservoirs is overturned by the quantification of drawdown areas. Nat. Geosci. 14, 402–408 (2021). https://doi.org/10.1038/s41561-021-00734-z