Details

Autor(en) / Beteiligte

• Cerdà-Domènech, Marc
• Rodellas, Valentí
• Folch, Albert
• Garcia-Orellana, Jordi

Titel

Constraining the temporal variations of Ra isotopes and Rn in the groundwater end-member: Implications for derived SGD estimates

Ist Teil von

• The Science of the total environment, 2017-10, Vol.595, p.849-857

Ort / Verlag

Netherlands: Elsevier B.V

Erscheinungsjahr

2017

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Submarine groundwater discharge (SGD) has been recognized as an important supplier of chemical compounds to the ocean that may influence coastal geochemical cycles. Radium isotopes (223Ra, 224Ra, 226Ra,228Ra) and radon (222Rn) have been widely applied as tracers of SGD. Their application requires the appropriate characterization of both the concentrations of tracers in the discharging groundwater and their distribution in the coastal water column. This study evaluates the temporal evolution of Ra isotopes and 222Rn concentrations in a dynamic subterranean estuary of a microtidal Mediterranean coastal aquifer that experiences large displacements of the fresh-saltwater interface as a necessary initial step in evaluating the influence of SGD in coastal waters. We show that changes in groundwater salinities due to the seaward displacement of the fresh-saltwater interface produced large variations in Ra activities in groundwater (by a factor of ~19, ~14, ~6, and ~11 for 223Ra, 224Ra, 226Ra and 228Ra, respectively), most importantly during rainfall events. In contrast, the 222Rn activities in groundwater oscillated only by a factor of 3 during these rainy periods. The large temporal variability in Ra activities hampers the characterization of the SGD end-member when using Ra isotopes as tracers, and thus presents a challenge for obtaining accurate SGD estimates. This study emphasizes the need to understand the hydrodynamics of coastal aquifers to appropriately constrain the Ra isotopes and 222Rn concentrations in groundwater and when applying both tracers in dynamic microtidal coastal systems. [Display omitted] •Ra isotopes and 222Rn were measured for nearly two years in a coastal piezometer.•High Ra variability was registered, especially during intense rainfall events.•222Rn displayed minor variations due to the no influence of groundwater salinity on radon emanation.•The hydrodynamics of coastal aquifers must be considered as essential to understand SGD fluxes.