Plant communities along preferential superficial water flow paths across a floodplain landscape

Abstract

From a hydrological perspective, is specially necessary to face the challenge of obtaining a complete spatial arrangement of the drainage network on floodplains with extremely flat relief, impermeable soils and exposed to periodic flooding. Focusing on a sector of the Flooding Pampa in Argentina, our aim was to gain a better understanding of the ways in which vegetation along preferential superficial water flow paths across a floodplain landscape differs from the matrix. We selected three sites along these flow paths, spanning a groundwater salinity gradient. Sampling points were located along transects, transversally arranged to surface and groundwater flows direction. Considering that alternating flooding and drought is an intrinsic characteristic of the region, the drainage network shows expansion and contraction cycles in response to variations in water availability. In this dynamics, preferential superficial water flow paths emerge in the floodplain landscape or disappear. The degree of expression of these paths depends on their location on the topographic gradient, because they tend to lose their degree of channelling as the ground relative heights decrease. Although in the first instance the vegetation matrix seems to be relatively homogeneous, the analysis on a detailed scale allows us to distinguish certain heterogeneity in that pattern. Our analysis shows that there is a downstream variation in the spatial distribution of the vegetation following the topographic and groundwater salinity gradients and that the degree of channelling and soil alkalinity determines the type of plant community to be developed in a certain site of the floodplain landscape.