TEMPORAL CHANGES IN CONCENTRATION, COMPOSITION AND SIZE DISTRIBUTION OF THE COLLOIDAL PHASE IN LAKE RISTEN, SWEDEN

The concentration and size distribution of colloidal matter (< 1.2 mu m) at different depths in the oligotrophic Lake Risten, Sweden, as wel l as in its main tributary were studied with light scattering in combi nation with photon correlation spectroscopy at least 4 times/year duri ng 3 consecutive years. Qualitative information on the composition of the colloidal phase was obtained from estimations of the colloidal Fra ction of Al, Fe, Mn and organic carbon as well as by a sequential leac hing procedure. The concentration of colloidal matter varied within a broad range (1.4-100 mg/l) in the stream, while the measurements in th e lake indicated minor changes (range 0.8-3.3 mg/l) between the differ ent sampling occasions as well as locations (both vertically and longi tudinally). Annual variations in the size ranges of the colloids (spri ng 120-340 nm; summer 280-700 nm: winter 200-500 nm) were observed. Th e changes in the average diameters of the colloidal population showed no correlation with changes in any general hydrochemical parameters, b ut the estimates of the fraction of colloidal organic carbon (COG) ind icated increased concentrations with increasing diameters.