Comparison of different tracer methods to assess natural recharg

Abstract

Groundwater resources in coastal aquifers may be threatened due to their scarcity and ova-use. Therefore, natural recharge becomes a critical issue since it is the main source tam in the absence of processes induced artificially. Different techniques are needed to assess natural recharge according to local characteristics. In addition, different methods applied to the same aquifer may display conspicuous differences. Tracer experiments in the vadose zone have several advantages to evaluate recharge yet they directly reflect the ion-site processes (they are direct), are sensitive to direct evaporation and we affected by transpiration when vegetation is present. In contrast, tracers may be selectively affected by physical or chemical soil processes and be no taken by plants, and the results may be biased by the measuring devices. This discussion was applied to two experiments in coastal aquifers of detrital nature: a small narrow strip under intensive agricultural practices and an extensive deltaic area. Different methods applied are compared. The validity of traditionally conservative tracers is discussed. Multiple mass balances permitted the different terms involved in the recharge process to be recogsised.