Identification of hydrogeochemical process linked to marine intrusion induced by pumping of a semiconfined mediterranean coastal aquifer

Abstract

This article analyses the hydrogeochemical processes, linked to the freshwater-seawater mixing zone, which can be caused by continuous pumping from a detrital coastal aquifer. It was necessary to construct an experimental plot, drilling three boreholes along a line perpendicular to the coast. A complete physico-chemical analysis was done of all water samples taken. The percentage of seawater, calculated from Chloride and 18 Oxygen concentrations, varied between 55 and 90 %. The ionic deltas (D) calculated, and the saturation indices (SI) of mineral phases susceptible to precipitation or dissolution, allowed a series of hydrogeochemical processes to be identified that occur as a consequence of the advance of marine intrusion into the coastal band, and of aquifer flushing. Based on the major elements, the fraction of exchange (bI) was calculated for samples ranging from seawater to freshwater, and this revealed that differences in bI could explain the hydrochemistry of the mixing zone. The main processes recognised include precipitation of dolomite, dissolution of gypsum, fixation of sulphur salts and cation exchange. Most of the ion exchange took place between Na and Calcium ? Magnesium ions. The process of fixation or liberation of these ions is probably determined by the advance or recession of the saline wedge, and/or by recharge during rainy periods. The behaviour of Magnesium is more sensitive to small variations in salinity, whilst Calcium behaves more homogeneously. The high percentage of seawater in the samples studied favours the speed and magnitude of processes such as ion exchange, and the intervention of magnesium is also a key.

Comparative Study of Microbial Diversity in Different Coastal Aquifers: Determining Factors

“…The interface is a strip of the aquifer where many chemical reactions take place, due to the mixing of waters with different characteristics [30][31][32]. Some of these reactions, such as metal oxidation/reduction, or denitrification, can be mediated by bacteria [12,[33][34][35][36][37][38][39].…”

Summarizing the impacts of future potential global change scenarios on seawater intrusion at the aquifer scale

“…In coastal areas, the problem is exacerbated due to overexploitation, intensifying SWI. Therefore, maintaining acceptable quantity and quality characteristics of GW reserves is important to ensure demand water supply (Sola et al 2013;Renau-Pruñonosa et al 2016).…”

A Methodology to Analyse and Assess Pumping Management Strategies in Coastal Aquifers to Avoid Degradation Due to Seawater Intrusion Problems

“…Some of them support towns with large populations as well as intensive agricultural and/or industrial activities. If surface water resources are scarce and/or intermittent -a frequent state of affairs on the Mediterranean coast -water supply must be partly or totally met using groundwater resources (Sola et al, 2013). They can be also useful to obtain nonconventional resources from desalination plants (Rodriguez-Estrella and Pulido-Bosch, 2009).…”