LIFE IN THE SINK: USING OSL TO ASSESS PAST, PRESENT, AND FUTURE HUMAN HABITATION IN THE DOWNSTREAM PORTION OF A MAJOR CONTINENTAL RIVER (Invited Presentation)

Fluvial systems mobilize and collect an abundance of resources, which are delivered by the channel network to their deltas. The resource-richness of deltaic "sinks" has proven timeless in terms of fostering human populations. For example, the Mississippi Delta can be seen as a "cradle of civilization" within the Lower Mississippi Valley and Gulf Coast, and continues to be economically and socially pivotal today. In addition to the benefits, fluvial landscapes are shaped by and subject to dynamic processes ranging from annual flooding to multi-centennial channel avulsions. Deltaic systems are further complicated by phenomena such as continuous subsidence and episodic storm events, and therefore are inherently difficult to lock-in-place in a way that is compatible with the establishment and maintenance of hard infrastructure. In other words, geohazards are also a timeless attribute of deltas.

Here, we give a synthesis of projects our team has established over recent years, using optically stimulated luminescence (OSL) chronology to enlighten prehistoric, contemporary, and future human:landscape interactions in the lowermost portion of the Mississippi River. We show that channel avulsions, sometimes initiated more than 700 km inland, influenced the pattern of sediment and freshwater delivery to the delta. Our advances in OSL chronology allow for identifying the timing of landscape occupation by prehistoric people, relative to the activation of the landscape through river avulsion. We find that prehistoric populations were sensitive to fluvial processes; they developed resilient strategies to use fluvial resources and appear to have carefully timed their occupation of sites to coincide with ideal stages of landscape maturity. We also show that the preindustrial rate of land gain in a large portion of the delta, fostered by delivery of sediment from the continental interior, was significantly lower than the post-industrial rate of land loss. This indicates net land loss in the densely-populated Mississippi Delta is likely to continue, and at least a portion of the contemporary loss is due to human perturbations over the past century. Our findings suggest that sustaining future communities within the "sink" of the Mississippi River will be a major challenge.