SYSTEM HETEROGENEITY AS VARIABLE FOR SOLUTE TRANSPORT IN STREAMS

Contaminant migration in streaming waters is characterized by a large number of physical and biochemical transfer mechanisms that often exhibit marked spatial and temporal variabilities. To quantify the mass transport and particularly the mass retention in bed sediments and biota, a process-based description needs to be combined with a stochastic interpretation of the constitutive parameters of the problem. In this study, constitutive parameters are conceived as stochastic fields in both space and time. Evaluation of phosphorus transport in a small stream in Sweden indicates that the heterogeneity (covariance structure) of partitioning with respect to solute/particulate adsorption and bed retention imposes significant effects on both statistically expected predictions and confidence intervals. Specifically, the temporal and spatial variability found for the partition coefficient was sufficiently pronounced to motivate that the coefficient is represented as an anisotropic random field in space and time. An analytical solution to the internal turnover mechanisms indicates that the effects of system heterogeneity increase markedly with time.