Salinization Processes in the Benichab Coastal Aquifer-Mauritania

摘要

A comprehensive and detailed study was conducted for the first time in the Benichab Region (western part of Mauritania) unique groundwater resource to identify the main process driving groundwater salinization using major and minor ions together with environmental isotopes. One hundred and nineteen samples were collected from 45 points (dug-wells and boreholes) during the period 2015 to 2017, where physico-chemical, chemical and isotope parameters were analyzed. pH values indicate circumneutral to basic (6.8 to 8.6) values while Electric Conductivity (EC) values show an increasing gradient from fresh groundwater lense (EC < 1 mS/cm) to highly saline groundwater in the vicinity of the Atlantic Ocean. In addition, TDS values range from 140 to 38,613 mg/l. Geogenic inputs reveal water rock interactions dominated by ion exchange, dissolution-precipitation processes and evaporation. Minor ions such as Br and B indicate that the salinization of groundwater in the study area comes from mixing between seawater through salt sea intrusion and fresh water where sea water represents a mean value of 8.42%. However, this marine source could increase with anthropogenic actions. According to δ-values, the mean values range for rainfall, from -3.8‰ and -25.04‰ for δ18O and δ2H, respectively; and for groundwater from -5.0‰ and -41.44‰ for δ18O and δ2H respectively. The isotopic characterization indicates fractionation processes such as evaporation and mixing of groundwater and seawater prevail in the unique source of potable water.