Isidorova Anastasija, Mendonça Raquel, Sobek Sebastian
Limnology, Department of Ecology and Genetics Uppsala University Uppsala Sweden.
Laboratory of Aquatic Ecology, Department of Biology Federal University of Juiz de Fora Juiz de Fora Brazil.
J Geophys Res Biogeosci. 2019 Mar;124(3):678-688. doi: 10.1029/2018JG004823. Epub 2019 Mar 28.
Freshwater reservoirs are important sites of organic carbon (OC) burial, but the extent to which reservoir OC burial is a new anthropogenic carbon sink is currently unclear. While burial of aquatic OC (by, e.g., phytoplankton) in reservoirs may count as a new C sink, the burial of terrestrial OC in reservoirs constitutes a new C sink only if the burial is more efficient in reservoirs than in other depositional environments. We carried out incubation experiments that mimicked the environmental conditions of different depositional environments along the land-sea continuum (oxic and anoxic freshwater, oxic and anoxic seawater, oxic river bedload, and atmosphere-exposed floodplain) to investigate whether reservoirs bury OC more efficiently compared to other depositional environments. For sediment OC predominantly of terrestrial origin, OC degradation rates were significantly lower, by a factor of 2, at anoxic freshwater and saltwater conditions compared to oxic freshwater and saltwater, river, and floodplain conditions. However, the transformation of predominantly terrestrial OC to methane was one order of magnitude higher in anoxic freshwater than at other conditions. For sediment OC predominantly of aquatic origin, OC degradation rates were uniformly high at all conditions, implying equally low burial efficiency of aquatic OC (76% C loss in 57 days). Since anoxia is more common in reservoirs than in the coastal ocean, these results suggest that reservoirs are a depositional environment in which terrestrial OC is prone to become buried at higher efficiency than in the ocean but where also the terrestrial OC most efficiently is transformed to methane.
淡水水库是有机碳（OC）埋藏的重要场所，但目前尚不清楚水库有机碳埋藏在多大程度上是一个新的人为碳汇。虽然水库中水生有机碳（例如浮游植物产生的有机碳）的埋藏可算作一个新的碳汇，但只有当陆地有机碳在水库中的埋藏效率高于其他沉积环境时，水库中陆地有机碳的埋藏才构成一个新的碳汇。我们进行了模拟陆地 - 海洋连续体中不同沉积环境（有氧和缺氧淡水、有氧和缺氧海水、有氧河床沉积物以及暴露于大气的洪泛平原）环境条件的孵化实验，以研究水库与其他沉积环境相比是否更有效地埋藏有机碳。对于主要源自陆地的沉积物有机碳，与有氧淡水、海水、河流和洪泛平原条件相比，在缺氧淡水和盐水条件下，有机碳降解率显著降低，降低了2倍。然而，在缺氧淡水中，主要源自陆地的有机碳向甲烷的转化比在其他条件下高一个数量级。对于主要源自水生的沉积物有机碳，在所有条件下有机碳降解率均较高，这意味着水生有机碳的埋藏效率同样较低（57天内碳损失76%）。由于缺氧在水库中比在沿海海洋中更常见，这些结果表明，水库是一种沉积环境，在其中陆地有机碳比在海洋中更容易以更高的效率埋藏，但陆地有机碳也最有效地转化为甲烷。
