Genesis, Distribution and Hydrochemical Features of Saline Groundwater

Global estimates of land area underlain with saline and brackish water aquifers are about 23.94 million km2 which is about 16% of the total land area on the earth. About 1.1 billion people live in these areas afflicted with groundwater salinity. Their largest occurrences are in the basins of West and Central Asia followed by the lowlands of South America, eastern Australia, and Europe. The genesis of salts in groundwater mainly involves the mechanisms; marine (connate marine groundwater, seawater intrusion, flooding, and spraying), natural terrestrial (evaporation from shallow groundwater tables, dissolution of salt-bearing sediments, membrane effects and hydrothermal igneous activities), and anthropogenic terrestrial mechanisms (irrigation return flows and pollutants). The key contributors are dissolution of salts (26% of the total area), evaporation from shallow groundwater (20%), and a combination of evaporation plus dissolution (13%). Connate water contributes to groundwater salinity in about 14% of the total area. Among the different regions, about 13.8% to the total global area with saline groundwater at shallow and intermediate depths exists in West and Central Asia. The geological regions underlain with brackish groundwater in countries like India, Pakistan, Iran, Iraq, Egypt, Saudi Arabia, Tunisia, Australia, China, USA, and Central Asia are elaborated. In addition to the genetic sources of salts, major hydro-geochemical processes also control the chemical characteristics of these waters.