[Seasonal Variation of Colloid Particles in the Shallow Well Water of a Small Watershed of Purple Soil].

Colloids are the major carriers of various contaminants during the downward transport into groundwater.To explore the long-term dynamics of colloid in the groundwater and its influencing factors,a one-year monitoring of colloid concentration and water physicochemical parameters was carried out in the shallow wells in a purple soil dominated watershed in the hilly region of central Sichuan.The results indicated that colloid concentrations within a year had a strong seasonal variation with the coefficient of variation being larger than 0.5.The maximum of colloid mass concentration could reach as high as 14.68 mg·L(the corresponding number concentration being 1.34×10 L),which occurred in the non-rainy season and was caused by the physical perturbations from water taken.Physical perturbations of rainfall led to the distinct peaks of colloid concentrations in the well water at the early stages of rainy season while it did not occur at the end of the rainy season even upon heavy storm.Water chemistries (EC,Ca,Mg,DOC) showed the dominant role in determining colloid concentrations and status in the well.The facilitated transport of contaminants (i.e.pesticides and heavy metals) due to the increased colloids in the shallow well water at the early stages of rainy season would potentially pose a great threat to the drinking water safety in the study area.Therefore,it is strongly suggested to increase the monitoring frequencies in terms of colloid concentrations and well water physicochemical parameters following the large rainfall events during this period.