The groundwater quality of Aruba, Bonaire and Curacao: a hydrogeochemical study

Groundwater resources on the Caribbean Islands of Aruba, Bonaire and Curaca o are limited and of poor quality. The groundwater of the islands is bracki sh, due to both seawater mixing and the semi-arid climate of the islands. T wo hundred and thirty water samples were collected to relate chemical varia tions in the groundwater of the three islands to the underlying differences in geology, and to define the natural versus anthropogenic influences. Bot h the chemical and isotopic (delta 18O, deltaD, and delta 37Cl) composition s of samples were determined. Several geochemical processes are recognised in the chemistry of the ground water samples. The most important processes are calcite dissolution, cation exchange, silicate weathering and potassium fixation. In (sub)urban areas anthropogenic influences affect the groundwater quality: high nitrate conce ntrations were measured. Infiltrating domestic and agricultural (waste)wate r replenishes the aquifer, and has a desalinization effect on the groundwat er quality. This phenomenon is primarily seen on Curacao, the most populate d island. Oxygen and hydrogen isotopic compositions of groundwaters from Curacao and Bonaire show that the samples are either meteoric water, or are affected by evaporation or seawater mixing. No distinction could be made between the l ast two processes. Only a few samples were measured for the Cl-isotope comp osition; all showed that no physical processes have taken place.