Hydrogeochemisty, isotopic composition and water age in the flow of a large catchment in the Argentine Pampas: Quequén Grande River, province of Buenos Aires, Argentina

MARTINEZ, DANIEL E.; QUIROZ LONDOÑO, O.MAURICIO; SOLOMON, KIP; DAPEÑA, CRISTINA; MASSONE, HECTOR; BENAVENTE, M. A.; PANARELLO, HECTOR

RIVER RESEARCH AND APPLICATIONS

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2016 vol. 33 p. 438 - 449

1535-1459

The Quequen Grande River (QGR) is a large catchment (10,000km2) in the Pampa Plain in Argentina. From November 2004 until April 2013 a hydrochemical and stable isotopes monitoring program was conducted, which include three sampling stations of monthly composite precipitation, weekly samples in two sites along the river, and several groundwater samples A standard data interpretation was initially performed applying standard statistics, Piper diagrams and δ18O vs δ2H diagrams. The time evolution of the values of δ18O in precipitation and streamwater were also determined. The integration of hydrogeochemistry and stable isotopes data indicates the existence of three main components of streamflow: 1) Baseflow: characterized by EC from 1200 to 1800 μs/cm and an isotope composition quite constant around δ18O -5.3? and δ2H - 33.8?. Water age for groundwater contribution is typically around 30 to 40 years using chlorofluorocarbons (CFCs). 2) Direct runoff: composed of channel interception and overland flow, which is of a low EC in the order of 50 to 100 μs/cm, and a highly variable isotopic composition; 3) translatory flow (pre event water that is stored within the subsoil ) with an intermediate EC and isotopic composition close to that of the weighted average composition of precipitation The hydrochemical and stable isotopic data allow the differentiation between baseflow and direct runoff. In addition to thus, CFC dating is a useful tool in assessing the dominance of baseflow in a stream. The data lead to a conceptual model in which an intermediate flow system, with mean residence time (MRT) of around 35 years, discharges into the drainage network. A regional flow system (MRT>50 years) discharges to the Ocean. It is concluded that in this large plain catchment streamflow separation, only two components can be applied in: a) short storm precipitation events having a high sampling frequency, b) during long dry periods when pre-event soil water is not released.