5/4/2023 0 Comments Aquamacs font adjustmentLas Cañadas aquifer system is a 216-km 2 steep area on the northern side of Tenerife Island that ranges from the sea to the summit of the Teide Volcano. In active volcanic islands having steep topography some additional processes must be considered, such as (1) the possibility of mixing chloride flow mass rates produced by recharge rates at different elevation (2) the variable rainfall-runoff partitioning and recharge mechanisms (3) the potential contribution of non-atmospheric chloride to groundwater and (4) the potential storage of chloride in the soil and vadose zones. For average net aquifer recharge, the CMB method is based on the steady balance of chloride mass fluxes from (1) atmospheric bulk deposition (2) surface runoff leaving the area and (3) recharge water just arriving to the water-table. The atmospheric chloride mass balance (CMB) method is of special interest for average net aquifer recharge at different spatiotemporal scales because it does not include E in the formulae thus reducing the overall uncertainty of estimates. Tracer techniques are an alternative methodology to the most widely used physical and hydrodynamic techniques for aquifer recharge evaluations (, and references therein). The combination of several techniques is a way to identify the sources of uncertainty involved. Results may be biased when compared with experimental measures, regional evaluations, and calibrated numerical models. For instance, most aquifer recharge predictions are evaluated as difference in precipitation and actual evapotranspiration ( E) deduced from non-global models. However, the evaluation of aquifer recharge is a complex task subjected to different kinds of uncertainty induced by the high spatial and temporal variability of precipitation, heterogeneities in soil and land use, few sampling and monitoring points, as well as the techniques used and the subsequent hydrological meaning and timing of estimates. Oceanic volcanic islands are often characterized by a rugged topography that favours conditions for enhancing recharge in summit areas where precipitation and aquifer recharge rates are usually higher than in the lowlands and coastal plains. This paper illustrates basic procedures and routines to use the CMB method for aquifer recharge in active volcanic oceanic islands having sparse-data coverage and groundwater receiving contribution of endogenous halides. This result is in agreement with potential aquifer recharge estimated through an independent lumped-parameter rainfall-runoff model operated by the Insular Water Council of Tenerife. Yearly net aquifer recharge was 631 mm year −1, i.e., 69% of yearly precipitation. The chloride-to-bromide molar ratio was an efficient tracer used to select recharge water samples having atmospheric origin of chloride. The potential contribution of chloride to groundwater from endogenous HCl gas may invalidate the CMB method. The wet hydrological year 2005–2006 was selected to compare yearly atmospheric chloride bulk deposition and average chloride content in recharge water just above the water table, both deduced from periodical sampling. with negligible surface runoff, which hosts the largest freshwater reserve in Tenerife Island, Canary Islands, Spain. The atmospheric chloride mass balance (CMB) method was used to estimate net aquifer recharge in Las Cañadas Caldera, an endorheic summit aquifer area about 2000 m a.s.l.
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