Vulnerability assessment of seawater intrusion in coastal aquifers of southern Bangladesh: Water quality appraisals

Abstract Overexploitation of groundwater, sea level rising, shrimp cultivation, etc. are the main causes of seawater intrusion in the coastal aquifers which is a growing concern around the globe. So to evaluate the seawater intrusion in the coastal aquifers of southern Bangladesh (Paikgachha, Khulna), water quality parameters such as pH (7.75–8.82), EC (371–5320 µS cm−1), TDS (182–2790 mg L-1), salinity (0.1–2.8 ppt), Na+ (14.8–1376 mg L-1), K+ (2.71–19.4 mg L-1), Ca2+ (33.2–192 mg L-1), Mg2+ (25–138 mg L-1), Cl- (18.2–3168 mg L-1), HCO3− (205–840 mg L-1), and CO32− (6.22–149 mg L-1) for 20 composite water samples, along with the hydro-geo-physical entities were utilized. Additionally, groundwater quality distributions were also appraised for identifying the suitable water sources for drinking and irrigation. Most of the sampling sites possessed mainly NaCl-type groundwater where Na+ and Cl- contents were 2–6 times higher than the recommended limits. Indices-based calculations indicated that only 35% of the sampling sites can provide good quality drinking water whereas groundwaters from >50% of sampling sites were unsuitable for irrigation. Statistical approaches reveal the potential seawater intrusion with trivial evidence of carbonate mineralization. Distributions of seawater intrusion vulnerability among the studied area were specified by the GALDIT index. The central (30%), southern (25%), and northern (45%) parts were identified as high, moderate, and low vulnerable zones, respectively due to saline water. Thus, considering the heterogenic distribution of seawater intrusion vulnerability among the studied unconfined aquifers, more intimate and detailed groundwater investigations are required on a periodical basis to explore water for drinking and irrigation.