Initial geochemical evidence of groundwater discharge in the floodplain of the Paraná River, Argentina, and its association with vegetation communities

MARCHETTI, ZULEICA Y.; CARRILLO-RIVERA, JOSÉ JOEL

Ontario

Congreso; 39 th IAH Congress; 2012

International Association of Hydrogeology

Groundwater flow is an active agent in diverse ecosystems and an important component of aquatic environments. However, due to the relatively large quantity of surface water, the presence and importance of groundwater have not been given consideration in the Paraná River floodplain, Argentina. This work aimed to identify groundwater flow systems and their association with vegetation in an island in the middle reaches of the Paraná River floodplain. Eight piezometers were installed in adjacent pairs in four vegetation communities at different depths to record groundwater movement in the vertical plane. Another eight piezometers were installed close to water bodies. The water table was recorded weekly for two years; twelve water samples were collected from piezometers, domestic wells, the river andother water bodies. Floristic composition and topographic elevation were registered for each vegetation community. The water level monitoring results from the piezometer installations suggested the study zone presents groundwater discharge conditions. Chemical and physical characteristics were used to identify different local flows zones and an intermediate flow zone. In relation to the recharge area, local rainfall showed an isotopic signature (δD and δ18O) similar to local flow zones detected in the study area. The chemical characteristics of the intermediate flow zone and the isotopic signature of local rainfall suggest that this flow zone would have travelled from a recharge area some 30 km outside the study area. Among identified vegetation communities, Willow and Plury-specific canopy forests are locatedon the highest topographic position. The Willow canopy is associated to recharge conditions of a local flow zone and the Plury canopy is linked to transit conditions of an intermediate flow zone. Tall grassland and marshy communities (located at an intermediate position and the lowest position, respectively) were associated to discharge areas of loca and intermediate flow zones. Water bodies had a distinctive quality suggesting a mixture of rainfall water, river water and groundwater in different proportions. The identification of both groundwater components (recharge, transit or discharge) and its related flow system hierarchy assisted in the interpretation of the relation between landscape and the dynamic of the biological communities.