Seasonal variability of groundwater quality in coastal aquifers of Kavaratti Island, Lakshadweep Archipelago, India

Abstract Lakshadweep Archipelago is comprised of several tiny coral atolls and scattered in the Arabian Sea off the south-west of India. Ground water is the only available fresh water resource for the islanders. The groundwater quality is decreased in this island due to population growth and anthropogenic activities like sewage dumping and agricultural activities. For this study, a total of 20 groundwater samples was collected randomly from the open wells that cover the entire area of the island. The physico-chemical parameters of groundwater were analysed in pre- and post-monsoon seasons during the year 2016–2017. The concentration of a majority of the chemical constituents exceeds the standards of WHO during post-monsoon than pre-monsoon season. EC content exhibited the violation of drinking water quality standards. The highest value of EC range 1023–6874 μS/cm recorded in post-monsoon than pre-monsoon. TDS concentration range from 574.6 to 1503.4 mg/l and 665–4468 mg/l in pre and post-monsoon seasons. Geochemical evolution diagram categories the groundwater facies into Na+-K+-Cl--SO42-, Ca2+-Mg2+-HCO3-, and Ca2+-Mg2+-Cl--SO42- in both seasons. Gibbs plot revealed that the evaporation is the dominant factor controlling the mechanism of ground water hydrochemistry. The water quality index suggested that both pre-monsoon and post-monsoon around 93.95% of the samples are unsuitable for drinking purposes. The suitability of groundwater for irrigation was studied by calculating the percent of sodium, sodium adsorption ratio, magnesium hazard and Reveille's index. The Wilcox and USSL plots also indicated that most of the groundwater samples are found to be unsuitable for irrigation. HFE diagram productively delineates that groundwater of the study area has strong influence of sea water in the fresh water aquifers. The highest level of significant correlation was observed between Mg-TH (r = 0.87), EC-TDS (r = 0.86), and Cl–Na (r = 0.77) respectively. As a whole, it is observed that the groundwater is not suitable for drinking, irrigation and industrial purposes due to the exceeding of chemical parameters from their standard limits. Therefore, groundwater management measures may be worked out regionally to improve water quality by artificial recharge, rain water harvesting, periodic disinfection of the wells and saving the fresh water stocks in the island accordingly.