Analysis of the spatial and temporal variations in the water quality of a karstic aquifer using UV spectrophotometry

This article presents a simple method based on the examination of ultraviolet multiwavelength absorptiometry of groundwater samples collected from a karstic aquifer, for direct and fast quality evaluation. The method provides information about the flow conditions of a karstic system, it helps with the monitoring of groundwater sampling during the pumping procedure and, finally, it gives an insight into the complexity of the spatial and temporal evolutions of the system. Application of this method to the study of a karstic experimental field situated in the south of France is subsequently presented. UV spectrophotometry used during investigations shows the hydraulic relation between two piezometers, and also between a piezometer and a surface watercourse. It stresses the influence of surface hydrology on water quality of this karstic aquifer. During periods of high flow, the water quality is the same in all the piezometers and is linked to the leaching of nitrates present in the upper surrounds of the aquifer; during mean or low flow, each piezometer presents a particular water quality depending on its local transmissivity.