Processes Affecting Wetland Changes in South Louisiana


Wetlands of coastal Louisiana are a byproduct of the interaction between Mississippi River water and sediment supply, and marine physical processes. Fluvial sediment has accumulated in deltaic and marginal deltaic depositional sequences during the constructive phase of development (rapid sediment accumulation), followed by a destructive phase where natural subsidence and erosion exceed the rate at which sediment and organics accumulate to maintain the integrity of wetland habitat.  Sediment carried away from the main river channel during flooding events was deposited throughout coastal Louisiana, forming the skeletal framework of the marsh ecosystem.  This cycle of natural flooding and deposition is directly responsible for the formation of wetlands over the past 6,000 years, and the current lack of sediment and flooding is directly responsible for much of the marsh and wetland loss being experienced throughout Louisiana today.

Human activities within the Louisiana coastal zone have changed the landscape of coastal marshes via direct excavation of land and indirect alteration of hydrology as a result of waterway and levee construction. Navigation channel construction and maintenance activities, hurricane and flood protection projects, and water control structures have altered large-scale hydrologic processes that maintain marsh resilience in chronically subsiding wetlands, whereas canal construction has segmented localized wetland habitat. Applied Coastal personnel have been evaluating the impact of natural and human activities on wetland changes at specific sites throughout south Louisiana for the past decade. Human-induced wetland changes have varying influences depending on the scale of impact. For instance, river levees and construction of dams within the Mississippi River watershed impact a much greater area over a much longer time period than do smaller waterways within relatively isolated wetland areas. Although both may impact marsh health, the degree to which one activity influences long-term change must be isolated at project scale to effectively mitigate changes via wetland restoration. Applied Coastal has provided expert analysis and advice on the causes of wetland change for many marsh locations in south Louisiana in support of effective marsh restoration strategies.

Wetlands, Louisiana