Relationship of dredged canals and wetland loss in Louisiana

The direct effects of converting wetlands to open water by dredging can be
magnified by indirect effects. For example, the dredged canal allows for
recovery of mineral fluids 1000s of m belowground which may induce
geological subsidence or faulting; dredged material deposited at the
surface to form continuous levees may create hydrologic stressors on the
wetland plants resulting in a conversion to open water habitat as a result
of both soil waterlogging and drying, less organic matter and sediment
accumulation, or greater erosion. We quantified indirect effects by
demonstrating a robust dose-response relationship between coastal land
loss and dredging canals in the Mississippi and Niger river deltas over 60
years. Importantly, the ratio of land loss to canal area increases with
time – a legacy effect. We also found that flood protection levees on the
main channel did not magnify the effect of dredging on wetland loss by
inhibiting sediment flow into adjacent wetlands along its banks.