Geochemical evolution of groundwater in the Pleistocene limestone aquifer of Barbados

This investigation is a comprehensive study of the hydrology and hydrogeochemistry of the Pleistocene limestone aquifer of Barbados, a tropical karst island aquifer. The purpose of this research is to investigate how groundwater compositions in a tropical karst aquifer vary spatially and temporally, and determine the factors or processes responsible for these variations. These questions are addressed by evaluating spatial and temporal variation of groundwater major and trace element and isotopic compositions, and thus determining relationships between groundwater composition variations and various hydrologic and geochemical factors. These factors include: recharge processes, groundwater flow paths, soil compositions, aquifer and aquitard rock compositions, and anthropogenic inputs. This research provides insight into natural processes that influence groundwater compositions, allowing us to: 1) better understand geochemical processes taking place in an aquifer; 2) use groundwater constituents as tracers to determine seasonal and interannual variation of recharge and to estimate recharge amounts; and 3) establish relative importance of land use and recharge processes in the susceptibility of a karst aquifer to contamination. Key results of this study include: 1) development of a method of determining the spatial and seasonal distribution of recharge, and determine interannual variations of recharge using oxygen isotopes; 2) determination that recharge has a greater influence on susceptibility of a karst aquifer to contamination than land use; and 3) spatial ad temporal variations of groundwater major and trace element and isotopic compositions reflect and respond independently to diverse processes, for example, seawater mixing and variations of the aquifer and aquitard rock compositions encountered along flow paths.