Both reduced and enhanced sediment supplies can threaten the persistence of salt marsh ecosystems. Sediment supplies are reduced when water is removed from rivers for irrigation, human consumption, and industrial use, or when overbank flooding is prevented by engineering works. Reduced sediment supply from the Mississippi River is one factor contributing to salt marsh loss in Louisiana.
Excessive sediments flow into salt marshes where the catchment has lost vegetative cover as a result of logging, farming, or development. Inflows also occur where mining operations discharge materials directly to streams. Wastes from California's gold rush are still making their way to San Francisco Bay. At a much smaller estuary, the marsh plain of Tijuana Estuary in southern California has elevated 25-35 cm since 1963 due to erosion from rapidly urbanizing canyons in nearby Tijuana, Mexico. The impacts have been losses of microtopographic variation and local species richness.
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