Présentations Colloques

Session 6.03: Innovative tools to improve understanding of groundwater recharge processes
Francisco J. (orateur)
First data on atmospheric chloride mass balance components in the Andean páramo in central Ecuador- implications to project climate scenarios of net aquifer recharge and potential groundwater chemical baseline
Screening of the impact of projected climate scenarios on groundwater quantity (net aquifer recharge, R) and quality (potential chemical baseline, CR) is a challenge because alterations due to global driving forces are being detected in rivers and aquifers. However, the evaluation of steady R and CR is a complex, uncertain task which is solved by adopting non-global techniques of questionable validity when using to project future scenarios. The atmospheric chloride (C) mass balance (CMB) technique is proposed for natural R and CR from precipitation (P). This technique (1) does not include actual evapotranspiration (E) in formulae, thus reducing the uncertainty in R, and (2) allows the evaluation of CR by combining atmospheric chloride bulk deposition (AP=P CP) and E.**The páramo, a tropical alpine highland in the 3000-4100 m elevation in the Andean region from Venezuela to Peru, is a main recharge area contributing to regional rivers and aquifers. In the Andean páramo in central Ecuador, the Pita and Tingo rivers basins, both including Neogene and Quaternary lava-flow and pyroclastic aquifers, were selected for sampling monthly P, CP, and chloride content in groundwater discharge (CR*) from local aquifers having low water-rock interaction. In both cases, per 100 m in elevation, P increases by 60 mm and CP decreases by 0.2 mg L−+1. Average AP is 1.65 and 2.11 g m−+2 year−+1 in the Pita and Tingo basins, respectively. As deduced from the 0.2 E-to-P ratio, average CR around 5 mg L−+1 and 8 mg L−+1 agrees with CR* data reported in both basins. The Cl Br ratio was used to identify the atmospheric origin of chloride in groundwater. Long CP and CR* time series are being compiled for modelling future scenarios of R and CR in this Andean region. **Research funded by the Ecuadorian PROMETEO Research Project CEB-014-2015 and the IAEA Research Project ECU 7 006.