The role of reservoirs in global sediment budgets

摘要

Man-made reservoirs are an important sink for sediment eroded from the land and thus constitute an importantaspect of the sediment budget. Their impact has mostly been assessed at the scale of an individual river basin butrarely on a continental or even a global scale. Although there are recent estimates of global sediment retention bydams,these studies have solely focussed on the role reservoirs play in controlling sediment fluxes to the oceans, thuson their net impact for global sediment budgets. However, the net impact of reservoirs is much larger than thegross amount of sediment stored within all reservoirs on the globe. Furthermore, the impact of smaller waterholdingstructures is mostly neglected. In this paper, we present a first comprehensive assessment of global annualsediment storage within reservoirs based on sedimentation rates obtained from over 3700reservoirs, representing nearly 25% of the global storage capacity. We argue that at least 27 petagrams (Pg)sediment are stored annually in all larger reservoirs, with possible sediment retention of an additional 27 Pg insmaller man-made water bodies. These values are 2 to 4 times larger than the estimated sediment mass transportedannually to the global coastal ocean, and 8 to 15 times larger than the net reduction of sediment flux to the oceansattributed to reservoirs. These estimates provide minimum annual continental erosion rates and comparison withsoil erosion data suggest that soil erosion on agricultural land is not the dominant source of sediment deposited inreservoirs or exported to the ocean. In recent decades, reservoir sedimentation has become as least as importantas floodplain sediment storage and can nowadays be considered as one of the most important sediment sinks incontinental sediment budgets.