Major ion chemistry and identification of hydrogeochemical processes of evolution of ground water ina small tropical coral island of minicoy, Union Territory of Lakshadweep, India

摘要

Major ion chemistry and identification of hydro geochemical processes of groundwater in the small island of Minicoy indicate that ground water occurs under phreatic condition and is seen as a thin lens floating over the saline water. The coral sands and coral lime-stones act as principal aquifers. The depth of the wells varies from 1.9 to 3.5mbgl and depth to the water table 0.62 to 1.75mbgl. The ground water is generally alkaline and EC varies from 592 to 2130 micromhos/cm at 25°C. The ground water is under Na+-SO_(4)~(2- )type and shallow meteoric percolation type and generally alkaline in nature. The factors affecting the quality of ground water are rainfall, tides, ground water recharge and draft, human and animal wastes, oil spills and fertilizers. Water samples collected from different parts of the island during pre-monsoon period and post monsoon samples had not been collected due to inaccessibility caused by rough weather. The water sample chemical analysis indicates that water type ranges from Ca-HCO_(3) (recharge type) to Na- HCO_(3) (Base Exchange water type). Among the cations Ca~(+) and Na~(+) and anions HCO_(3)~(-) and Cl~(-) dominate the ionic concentration in groundwater which made the water both recharge and base exchange water types. The hydrochemistry is mainly controlled by evaporation, partly influenced by water-rock interaction and aquifer materials. The chloro alkali indices of water samples of Minicoy atoll are negative indicating the ion exchange predominance in the study area. The rock water interaction played major role in the evolution of water chemistry, which was partly by evaporation process also. The ground water in the study area is generally suitable irrigation for all types of soil.