Sand as a stable and sustainable resource for nourishing the Mississippi River delta

The Mississippi River delta is undergoing a catastrophic drowning, whereby 5,000 km(2) of low-lying wetlands have converted to open water over at least the past eight decades(1), as a result of many anthropogenic and natural factors(1-3). Continued net land loss has been thought inevitable due to a decline in the load of total suspended sediment-both sand and mud-carried by the river(4). However, sand-which accounts for similar to 50-70% ofmodernand ancient Mississippi delta deposits(5,6) but comprises only similar to 20% of the sampled portion of the total load(3)-could be more important than mud for subaerial delta growth(5). Historically, half of the Mississippi River sediment load is supplied by the Missouri River(3). Here we analyse suspended sediment load data from two locations downstream from the lowest Missouri River dam to show that the measured sand load in the lower 1,100 km of the Mississippi River has not significantly diminished since dam construction. A one-dimensional numerical model of river morphodynamics predicts that the sand load feeding the delta will decrease only gradually over the next several centuries, with an estimated decline from current values of no more than about 17% within the coming six centuries. We conclude that the lower Mississippi River channel holds a significant reservoir of sand that is available to replenish diminished loads via bed scour and substantially mitigate land loss.