Ecogeomorphic Feedbacks that Grow Deltas

Abstract

Coastal river deltas are complex and dynamic ecosystems where vegetation plays an essential role in influencing, as well as being influenced by, physical processes, creating ecogeomorphic feedbacks between vegetation canopy characteristics and topography. However, this feedback is poorly understood. This knowledge gap is due to difficulties in detecting and quantifying the interactions that define the feedback. Emerging technology and data analysis techniques like transfer entropy have made it possible to overcome former difficulties associated with sampling constraints and delineate bidirectional feedback within many vegetation classes at the delta scale. Here the transfer entropy analysis was consistent with widespread understanding of marsh zonation, yet produced additional insight into which vegetation classes specifically had a dominant impact on topographic change. Ecogeomorphic feedback was resolvable only within native vegetation classes (Nelumbo and Polygonum) that occur over low to moderate elevations within the Wax Lake Delta Louisiana. In contrast, nonnative vegetation classes (Colocasia and Eichhornia) were not as effective at accreting sediment as native classes. The transfer entropy analysis suggests that different vegetation communities play functionally different roles in landscape evolution that should be differentiated in ecogeomorphic models. Within such models, it would be most imperative to resolve detailed flow characteristics at lower to low-middle island elevations. Furthermore, within elevation zones, it is likely important to differentiate between the roles of multiple vegetation communities rather than treating the entire elevation zone as a single ecogeomorphic entity.