THE HYDROLOGIC LANDSCAPE OF THE AJÓ COASTAL PLAIN, ARGENTINA: AN ASSESSMENT OF HUMAN-INDUCED CHANGES

Coastal wetlands rank among the most endangered ecosystems since they are affected by the sea level rise and by anthropogenic activities. The continued loss and degradation of these valuable environments requires that a great deal of attention be given to groundwater-surface water exchange, as the ecological function of coastal wetlands greatly depends on it. Hydrological research carried out in the lower part of the Samborombón Bay coastland (Río de la Plata estuary, Argentina) by remote sensing revealed the presence of a meandering channel system, which does not appear in modern maps. The analysis of SPOT satellite images, the interpretation of historical maps and in situ surveys confirmed that this structure is part of an ancient river system, the palaeo-Rincón de Ajó River, at present almost completely silted up. In addition, multispectral satellite data provided the information to develop a conceptual hydrological model, as well as evidence that a significant hydrologic landscape shift occurred due to man-made interventions. The palaeo-Rincón de Ajó River disappeared because the water flow in its upper course was intercepted by man-made canals, and in its lower course the embankments built for the construction of roads and to prevent the flooding of the wetlands from the Río de la Plata estuary excluded the surface flow from the estuary to the mainland and vice versa. The silting up in the lower course and in the vicinity of the mouth cancelled the original structure of the ancient river.