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 μm) at different depths in the oligotrophic Lake Risten, Sweden, as well as in its main tributary were studied with light scattering in combination with photon correlation spectroscopy at least 4 times/year during 3 consecutive years. Qualitative information on the composition of the colloidal phase was obtained from estimations of the colloidal fraction of Al, Fe, Mn and organic carbon as well as by a sequential leaching procedure. The concentration of colloidal matter varied within a broad range (1.4–100 mg/l) in the stream, while the measurements in the lake indicated minor changes (range 0.8-3.3 mg/l) between the different sampling occasions as well as locations (both vertically and longitudinally). Annual variations in the size ranges of the colloids (spring 120–340 nm; summer 280–700 nm; winter 200–500 nm) were observed. The changes in the average diameters of the colloidal population showed no correlation with changes in any general hydrochemical parameters, but the estimates of the fraction of colloidal organic carbon (COC) indicated increased concentrations with increasing diameters.