the Science of the Total Environment A.--b-- u.k-dr-I*Lyu ELSEVIER The Science of the Total Environment 188 (1996) 87-99 Temporal changes in concentration, composition and size distribution of the colloidal phase in Lake Risten, Sweden Anna Ledin”, Stefan Karlsson, Karsten Hikansson, Per Sand&n, Anders Diiker Department of Water and Emironmental Studies, Link5ping University. S-581 83 LinkCping, Sweden Received 10 November 1995: accepted 7 May 1996 Abstract The concentration and size distribution of colloidal matter ( < 1.2 pm) 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 tlie 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. Key~o&r Colloidal phase; Hydrochemical parameters; Organic carbon; Seasonal changes; Light scattering 1. Introduction Interactions with colloidal and suspended mat- ter in fresh waters have a large impact on the mobility and redistribution of numerous elements [1,2]. Field studies have shown that many transi- tion metals as well as lanthanides and actinides can be associated with solid matter, both in sur- face and groundwaters [3- 1 I]. * Corresponding author. Relatively little attention has been paid to the colloidal phase ( < 1 Llrn) itself and associated trace elements, although this size class usually contributes a large surface area in many natural waters. The tendency of colloidal matter to ag- glomerate would be of importance for the distri- bution of trace compounds between mobile colloidal carriers and the stationary sediments. Agglomeration and dispersion processes are difficult to predict since the properties of the autochtonous mineral phases are continuously modified by surface coatings of humic matter 004%9697/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved PZI SOO48-9697(96)05161-3