Hydrochemical and isotopic assessment of the Iberá hydrogeological system in NE Argentina

MANZANO, MARISOL; RODRÍGUEZ, LETICIA; HEREDIA, JAVIER; VIVES, LUIS; NITTMAN, JUAN; ZABALA, MARÍA EMILIA; VALLADARES, ANDREA; AGARWAAL, PRADEEP; ARAGUÁS, LUIS

Viena

Encuentro; EGU General Assembly 2011; 2011

European Geosciences Union

The Iberá wetland system overlies a large Pliocene-to-present alluvial fan of the Paraná River. The wetlands substrate is formed by fine to coarse quartz sands with silt and clay layers corresponding to alluvial sand bars, eolian dunes and fluvial beds (Ituizangó and Toropí formations). Abandoned beds of anastomosed streams are occupied by large, very shallow and mostly NE-SW elongated lagoons called esteros, covering 13200 km2. To the north and northeast of the Iberá system the sandy formations overlie basalts (Serra Geral formation) with sandstone intertraps (Solari formation), which deeps to the SW; to the west and south they underlie silts and fine sands of the Fray Bentos and Paraná formations. The prevalent hydrological model indicates that the esteros receive mostly pluvial water, with some shallow groundwater discharge. The whole wetland system drains to the SW, discharging into the Corrientes River which, in turn, flows into the Paraná River. To understand the hydrology of the system and its relationship with the aquifers in the area, two water sampling surveys were performed in September 2009 (14 samples) and August-October 2010 (23 samples). Water samples were taken from esteros, the Corrientes River and from wells taping different layers and depths. Major and some minor components, electrical conductivity (EC), pH and temperature were measured in all samples. In the 2009 samples the isotopes 18O, 2H. 3H, 13C and 14C were determined. In the 2010 survey, the activity of 222Rn was measured in situ with a portable RAD7-RADAQUA equipment. Geological information suggests that deep wells in the SE (90-120 m) tap red sandstone formations under the basalts, assumed to belong to the Guaraní Aquifer System formations (GASF); shallow wells in the SE tap sands of the Toropí formation (TF); wells sampled to the NE and N (60->100 m deep) probably tap a variety of infra, intra and supra basalt sand layers (GASF; Solari formation and IF, respectively); wells sampled to the W (