On Distribution Coefficients in Aquatic Systems

Sammanfattning: In this thesis, different types of chemical and physical distribution coefficients are identified, examined and used to describe the fate and transport pathways of substances in aquatic systems.Observations from field experiments in streams with non-reactive and reactive tracers constituted the basis for development of an advection-dispersion model. Differences in the concentrations in both the water and sediment data for the tracers were due to the particle affinity of the reactive tracer. This difference in behaviour could be described by including an instantanous and a kinetically controlled sorption, which included distribution coefficients, in the water column (Kd) and in the streambed sediment (KB), respectively.The results presented in this thesis also include a model for the lake characteristic concentration of suspended particulate matter (SPM). The SPM-model can be used to describe mass flows of particles in lakes. The traditional distribution (or partition) coefficient Kd has been found to be unsuitable for interpretations of the particle association of solutes and also for distributing solute mass flows. Instead, the particulate or the dissolved fraction, PF and DF, defined as ratios of the particulate or dissolved concentration to the total concentration respectively, is recommended for mass-balance calculations. A new PF-model for phosphorus has meant that this part is no longer the most sensitive part of predicting concentrations of phosphorus in lakes using a more extensive dynamic model.New methods have also been developed to describe the shape of lakes. Together with the mixing depth of lakes, the shape of a lake can be transformed into a distribution coefficient that physically determines the portion of a lake that is exposed, both areally and vertically, to continuously mixing.