INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
Caracterización hidroquímica e isotópica de las cuencas de los arroyos Tamangueyú, Seco y El Moro, provincia de Buenos Aires, Argentina
QUIROZ LONDOÑO, O.MAURICIO; MARTINEZ, DANIEL E.; DAPEÑA, CRISTINA; MASSONE, HECTOR
Congreso; VIII Congreso Latinoamericano de Hidrología Subterránea.; 2006
ASOCIACIÓN LATINOAMERICANA DE HIDROLOGÍA SUBTERRANEA PARA EL DESARROLO (ALHSUD)
The catchments of the Tamangueyú, Seco and El Moro creeks are placed in the area called Inter-mountain Plain of the Province of Buenos Aires, Argentina, covering an area of about 2000 km2. The sources of these streams lie in the southwestern spurs of the Tandilia range, which is formed by a crystalline basement and lower Paleozoic sedimentary rocks. While the two first outflow into the Quequen river, the latter outflows directly into the Atlantic Ocean. It is difficult to identify watersheds and directions of flow in the area as a consequence of the extremely low gradients. Groundwater occupies a major place in the sustainability of the agricultural produce. Furthermore, it is the only source of fresh water supply for the neighboring towns. Then, it becomes necessary to improve the knowledge of the flow processes and to characterize the water resources qualitatively. The aim is of this paper is to characterize the hydrochemistry and isotopic composition of the considered catchments in order to determine the spatial distribution of qualitative features of groundwater and to identify recharge areas, directions of flow and groundwater-surface water relationships. Composite rain water samples were collected in two sites and a hydrogeochemical monitoring campaign was performed during 2005/06-summer season including 70 shallow wells. Major ions plus silica and nitrate were analyzed applying standard techniques, and a smaller number of samples were selected for environmental isotope (2H and 18O) measurements. Hydrochemical diagrams, scatter plots and distribution maps for different components and/or parameters were used in the interpretation of data. Electrical conductivity distribution shows an increasing trend from watershed to the coast, in good agreement with the map of piezometric contours. The use of distribution maps for other components and ionic ratios, specially the ratio HCO3-/Cl- have proved to be useful to delimite recharge areas and to observe in detail the behavior of flow in flat areas. Using these tools it has been possible to recognize a change in the behavior of the Seco creek at midd-watershed, moving from gaining stream to losing stream. The Piper diagrams and the Stiff diagrams included in maps show a clear differentiation between groundwater in the catchment of El Moro creek, where a higher chloride proportions occur, respect to the other two catchments where all the samples correspond to the bicarbonate type with a lower chloride participation due to its shorter flow path before outflowing into the Quequen river.