Ricardo Sanchez-Murillo, National University, Stable Isotopes Research Group and Water Resources Management Laboratory, Heredia, Costa Rica, Germain Esquivel-Hernandez, Universidad Nacional, Escuela de Quimica, Heredia, Costa Rica, Alicia Beatriz Correa Barahona, University of Costa Rica, Department of Geography and Water and Global Change Observatory, San Jose, Costa Rica and Christian Birkel, University of Aberdeen, Aberdeen, United Kingdom