CHARACTERIZATION OF NATURAL COLLOIDS FROM A RIVER AND SPRING IN A KARSTIC BASIN

Colloids are known to transport contaminants over long distances in na tural media. Despite this potentially harmful effect, very few studies have been undertaken in subsurface aquifers. This paper presents the first results of a study of natural colloids and particles in a karsti c aquifer. The site was chosen for its coverage by clay layers and pea t which deliver various and numerous particle types in water. The meth odological part describes three methods used for size determination an d sample fractionation of surface water and spring water. These method s have been adapted for the treatment of multiple samples due to the r apid discharge variation typical of karstic aquifers. The analysis of many particle size distributions (PSD) shows that they can be describe d by a Pareto law. The variation of the slope of the PSD at the spring is mainly dependent on discharge. This behavior is interpreted as a w ashing of the karstic drains during the first phase of high flow event s. Fractionation of the samples allowed application of various charact erization techniques to particle size classes. X-ray diffraction (XRD) patterns showed that most of the mineral particles originated from Qu aternary deposits and limestones. However the use of scanning electron microscopy with energy-dispersive spectrometer (SEM-EDS) detailed the composition of individual particles and revealed particles not found by XRD. These techniques also showed the high complexity of the natura l particles and the important place of coprecipitation in their format ion. Consequences on the fluxes of particulate matter and its potentia l role as a carrier of contaminants are discussed.