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.