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.

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

“…The alternation of periodic floods and droughts is a distinctive feature of the region that determines very different spatial patterns of surface water arrangement depending on water availability in the system (Aliaga et al, 2016; Fajardo et al, 2022; Salese & Lara, 2022; Vercelli et al, 2019). In particular, waterlogging in the Flooding Pampa is a disturbance process that impacts plant community structure (Chaneton et al, 1988; Entraigas et al, 2017; Entraigas et al, 2019). Our results indicate that, independently of changes in vegetation structure, periods of excess water modify a central element of grassland functioning at the landscape scale, such as the dynamics of their net primary productivity, something that has already been demonstrated at a regional scale in previous work (Lara et al, 2020).…”

Surface soil moisture variability in a sector of a humid basin characterized by extremely flat relief

“…Petrocalcic horizons are a common feature of these soils, mainly composed of silts with variable amounts of calcium carbonates and a heterogeneous internal structure (Dietrich et al, 2014); furthermore, their hardness, thickness, morphology and depth may vary in short distances (Pazos & Mestelan, 2002;Weinzettel et al, 2009). The vegetation matrix of the landscape is, in fact, a mosaic formed by graminoid steppes and prairies with different cover and height of grasses (Entraigas et al, 2019;Vercelli, 2011Vercelli, , 2018. The climate is temperate humid with a mean annual temperature of 14.4 C and a mean annual precipitation of 962 mm recorded at the Azul Aero Meteorological Office of the National Meteorological Service (15 km from the field site) over a 30-year period (1989-2018).…”

Esquema explícito para la solución numérica del flujo no saturado en medios heterogéneos bajo condición de niveles freáticos someros.

“…En el sector más bajo, sumamente llano, con sus suelos nátricos y drenaje deficiente, se desarrolla principalmente la cría ganadera extensiva en una matriz de pastizales naturales interrumpida por las numerosas cubetas y lagunas de carácter mayoritariamente semi-permanente y por dunas parabólicas y longitudinales (Entraigas et al, 2019).…”