Land loss due to human-altered sediment budget in the Mississippi River Delta

Land loss in the Mississippi River Delta is due to the human-altered sediment budget, yet the relative contributions of building dams, levees and extracting subsurface resources are unknown. Here, using numerical models, we show how each cause contributed to the land loss crisis in Barataria Basin within the Mississippi River Delta. Before human interference, Barataria Basin had a sediment budget surplus, and the excess sediment would have grown the wetlands at 7–13 km 2 yr −1 . Dam building in the Mississippi River basin decreased overbank fluvial sediment deposition in Barataria by a third, yet the basin-wide sediment surplus persisted. The installation of flood-protection levees eliminated overbank sediment deposition and created an annual basin-wide sediment deficit, leading to land loss of 7 km 2 yr −1 . During its peak, subsurface resource extraction enhanced the deficit and doubled the land loss rates. Our findings show that these three causes can explain the land loss crisis, and the recent slowdown in land loss is linked to the declining rate of resource extraction. Finally, we find that the effect of dams is secondary to levees and resource extraction, which implies that sediment supply reduction may not be as detrimental to sediment diversions and coastal restoration as previously thought.