Sediment Grain Size Affects Vegetation Patterns in River-Dominated Deltas

Abstract

River deltas contain some of the most densely populated areas in the world and are characterized by a rich biodiversity and highly productive ecosystems. Although previous studies have revealed that sediment grain size plays a key role in determining delta morphology, its subsequent effects on deltaic vegetation distribution patterns remain elusive. We used a theoretical templet to facilitate our study by conducting numerical experiments to simulate deltaic morphological evolution in response to various sediment grain sizes and explored the vegetation distribution determined by the elevation profile of a typical river-dominated delta. Our results showed that a fine-grained, cohesive delta would develop vegetation patterns transitioning from high- to low-elevation adapted vegetation species with increasing distance, whereas the same vegetation transformation trend could occur with decreasing distance to the center of a large-grained, noncohesive delta. The modeled vegetation distribution pattern of fine-grained, cohesive and large-grained, noncohesive deltas could be well demonstrated in the natural deltas. In addition, vegetation distribution patterns are related to the grain size-driven morphological processes of deltas, and the leading role of cohesive and noncohesive sediments on constructed delta is critical in determining the resulting vegetation distribution pattern. The dominance of each vegetation type would gradually become stable as delta matures. The interspecies competitions could influence distribution patterns of each vegetation type by enhancing the fragmentation of mid-elevation adapted vegetation. The effects of sediment grain size on the deltaic vegetation patterns associated with a delta’s morphological processes have potential implications for the conservation and restoration of deltaic habitats.

Keywords: river-dominated delta, sediment grain size, deltaic morphology, vegetation distribution pattern