Vegetation changes in coastal wetlands of the outer estuary of the Río de la Plata as a result of anthropic-induced hydrological modifications

Abstract

Samborombón Bay in Argentina is one of the largest coastal wetlands of South America. The Ajó wetlands are located to the south of Samborombón Bay and despite being protected natural areas, the land is privately owned and used for extensive cattle ranching where producers build embankments to reclaim salt marshes land and expand cattle grazing areas. The aim of this study is to identify the occurrence of embankments in the landscape of the Ajó coastal wetlands, to describe their effect on-plant communities' structure (composition and species abundances), and environmental features (soil and water physical and chemical variables). Embankments were mapped using satellite images and aerial photographs. Based on the mapping, 7 sampling areas of marshes with embankments were selected for the study of vegetation, water, and soil. Each sampling area has an embankment that interrupts a tidal channel dividing the marsh into two sectors, one connected to the tidal flow and the other disconnected. Vegetation and soil sampling were performed along a transect covering 3 relative topography levels (High salt marshes, Low salt marshes, and Mudflat-tidal channel) on each side. The results show that embankments and livestock activity modify the plant community structure and environmental features. Disconnected marshes compared to connected ones have a higher abundance of grassland species, freshwater species, salt-tolerant species, and exotic species. Surface water has a greater range of variability in electrical conductivity and the majority ions and soil salinity is higher in disconnected high marshes than in connected ones. In a context of global change, there is uncertainty about the tendency of these observed changes. In this sense, the study carried out based on the monitoring of vegetation, soils, and water is a relevant tool for detecting environmental impacts in wetlands whose hydrology has been anthropically modified.