Marine sediment sustains the accretion of a mixed fluvial-tidal delta

There has been a decline in fluvial sediment inputs to the world's deltas but it is still unclear to which extent upstream changes in sediment supply directly relate to variations in wetlands extent. We address this gap by investigating the contribution of marine and fluvial sediment sources to tidal flats in Changjiang Delta. Surprisingly, field measurements show that tidal flats accreted despite a > 50% decline in fluvial suspended sediment discharge due to the Three Gorges Dam. Results show that at a decadal time scale only a minimal portion of fluvial sediments contribute to sediment deposition on tidal flats while the adjacent estuary and ocean zone contributed over 90% of the deposit. We conclude that marine sediments give a substantial contribution to the maintenance of coastal wetlands and that there can be a long-time lag between human interventions and the delta's response to the decline in sediment supply.