Monday, 15 December 2014
Anna Elizabeth Braswell and James B. Heffernan, Duke University, Nicholas School of the Environment, Durham, NC, United States
Coastal wetlands provide valuable ecosystem services, but are threatened by sea level rise, anthropogenic disturbance, and changing sediment supply. Watershed characteristics, such as watershed area and upland land use, can mediate suspended sediment concentration; while estuarine characteristics, such as fetch, can determine the wave energy and erosion in a coastal area. These combined effects are mediated by local biogeomorphic feedbacks within wetlands to determine wetland extent. There has been little empirical or theoretical study of how broad-scale features of estuaries and watersheds influence wetland formation, persistence, and loss. As such, we cannot predict how wetland extent and resilience to sea level rise will respond to land use change and other human alterations. In this study, we ask, what factors control the broad-scale distribution of coastal wetlands? We examined relationships between coastal wetland extent and watershed/estuarine characteristics at multiple scales along the Eastern and Gulf coasts of the United States. Using existing GIS resources, we delineated the absolute and relative extents of coastal wetlands, and generated watershed and estuarine characteristics to serve as proxies of sediment input, the estuarine energy environment, and local wetland alteration. We found that present coastal wetland distributions reflect interactions across a wide range of spatial scales, ranging from local biogeomorphic processes, to estuarine-scale morphology that governs hydrodynamics, and to past and present watershed processes that influence sediment delivery. Coastal wetland extent scales with estuary size to the half power and the residuals reflect a bimodal distribution. The wetland extent distribution also displays multiple clusters, possibly signaling that local feedbacks drive wetland extent at some scales. When the results are broken up by region, this pattern is stronger in Northeastern United States. Using continental-scale variation in watershed and estuarine characteristics to understand where and how coastal wetlands have established, we hope to predict how wetland distributions will respond to sea level rise, altered sediment concentrations, and anthropogenic disturbance.