River delta sediment trapped by marshes

An intermediate amount of marsh vegetation enhances sedimentation in river deltas, according to a study published online in Nature Geoscience. This finding may help to guide restoration strategies in river deltas, such as those in the Mississippi River delta region, USA, that are under threat as sea levels rise.

William Nardin and Douglas Edmonds used a numerical model and observations of Wax Lake Delta in Louisiana, USA, to study how marsh vegetation influences the transport of sediment in river deltas. They found that vegetation of intermediate height and density is optimal for the deposition of sand and mud. However, if the plants are too tall or densely packed, sand tends to remain in the river channel and marsh sedimentation is reduced. This implies that the timing of the floods, storms, or engineered diversions that deliver sediment-laden waters to deltaic marshes, relative to the seasonal growth of marsh vegetation, can determine how effectively these marshes enhance land building.