FLUVIAL AND METEOROLOGICAL CONTROLS on WETLAND DEVELOPMENT IN THE CHENIER PLAIN

Located at an interface between the land, the atmosphere and the ocean, the Mississippi River Delta is among the most sedimentary active environments on earth. Sediment dynamics in this zone are driven by a combination of alluvial processes that generally import sediment to the system, storms and waves that can lead to sediment accumulation, residstribution, or export, and subsidence, that both increases accomodation space and can lead to land loss. The classical view of deltaic wetland development is that it occurs when as velocities decrease when the Mississippi River reaches the open ocean, causes sediment to settle out. However, we now recognize the role of storm-driven reworking coastal sediments as an additional pathway for wetland development. One region where this occurs is the Chenier Plain in southwest Louisiana, which is comprised of alternating shelly ridges and muddy swales that are genetically related to changes in the course of the Mississippi River. Here we show that interior wetland formation in a small lake (Miller Lake) in the Chenier Plain occcurred in recent decades, and is linked to increases in flow in the Atchafalaya River and storm-driven sedimentation. A series of five sediment cores from Miller Lake show the development of a marsh, with an increasing frequency of event horizons (e.g. storm deposits), in near the surface of the cores. A ²¹⁰Pb geochronology from one core indicates that sedimentation increased after ~ 1970, nearly contemporaneous with delta development at the Wax Lake and Atchafalaya River Deltas. Taken holistically, these findings suggest that the increased flow the Atchafalaya River that occurred in the mid-20th century led to increased sediment concentrations in the nearshore zone of the Chenier Plain. Storms and other high energy events were able to resuspend these sediments and emplace them in interior ponds, thereby allowed a marsh to development. These findings suggest that downdrift sediment loads from large rivers may prove to be a pathway for coastal restoration.