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.