Estimating groundwater residence time and recharge patterns in a saline coastal aquifer

Abstract

A detailed study using environmental tracers such as chloride (Cl−) and tritium (3H), deuterium (2H) and oxygen (18O) isotopes was performed in an alluvial coastal aquifer in two contrasting environments (urban and agricultural). These environmental tracers combined with a high‐resolution multi‐level sampling approach were used to estimate groundwater residence time and recharge patterns and to validate the hydrogeochemical conceptual model already proposed in previous studies. δ18O and δ2H combined with Cl− data proved that the hypersaline groundwater present in the deepest part of the aquifer was sourced from the underlying hypersaline aquitard via an upward flux. Both chemical and isotopic data were employed to calibrate a density‐dependent numerical model based on SEAWAT 4.0, where 3H and Cl− were helped quantifying solutes transport within the modelled aquifer. Model results highlighted the differences on estimated recharge in the two contrasting environments, with the urban one exhibiting concentrated recharge because of preferential infiltration associated to the storm water drains network, while scarce local recharge characterized the agriculture setting. In the urban field site, is still possible to recognize at 9 m b.g.l. the input of the atmospheric anthropogenic 3H generated by testing of thermonuclear weapons, while in the agricultural field site, the 3H peak has been washed out at 6 m b.g.l. because the groundwater circulation is restricted only to the upper fresh part of the aquifer, drained by the reclamation system. The presented approach that combined high‐resolution field monitoring, environmental tracers and numerical modelling, resulted effective in validating the conceptual model of the aquifer salinization. Copyright © 2016 John Wiley & Sons, Ltd.

Coastal aquifer response to extreme storm events in Emilia‐Romagna, Italy

“…The surface hydrographic system and water discharge towards the sea is guaranteed by a capillary drainage network. Several natural and anthropogenic features threaten this area: saltwater intrusion in the unconfined aquifer and seawater encroachment inland along the rivers (Giambastiani, Antonellini, Oude Essink, & Stuurman, 2007); palaeo-seawater upward seepage through the hypersaline aquitard (Caschetto, Colombani, Mastrocicco, Petitta, & Aravena, 2016;Colombani, Osti, Volta, & Mastrocicco, 2016a); natural and anthropogenic land subsidence (Taramelli, Di Matteo, Ciavola, Guadagnano, & Tolomei, 2015); soil salinization (Colombani et al, 2016b); high demand of water during the tourist season; insufficient aquifer recharge; and sea level rise (Antonellini et al, 2008).…”

Deriving Natural Background Levels of Arsenic at the Meso-Scale Using Site-Specific Datasets: An Unorthodox Method

“…Horizontal groundwater flow directions, hydraulic conductivity, and hydraulic gradients are extremely variable due to aquifer heterogeneity and complex sand-body geometry. The hydraulic head is close to the ground surface (max depth of about 1 m bgs) [59,60] and is generally dominant with respect to the deeper confined aquifers. Recharge of A0 is almost exclusively vertical, by rainfall or irrigation [61].…”

Delineation of Suitable Zones for the Application of Managed Aquifer Recharge (MAR) in Coastal Aquifers Using Quantitative Parameters and the Analytical Hierarchy Process

“…In coastal zones, multilayer sampling is critically important to define the vertical distribution of salinity [51], while the determination of groundwater residence time [52] could further increase the effectiveness of MAR application. Although the SuSAM index was developed to be compatible with a coastal hydrogeological environment, parameters of agricultural activities and nitrate pollution could be included in the method with the aim of reducing nitrate pollution [53].…”