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 exhi bit marked spatial and temporal variabilities. To quantify the mass tr ansport and particularly the mass retention in bed sediments and biota , a process-based description needs to be combined with a stochastic i nterpretation of the constitutive parameters of the problem. In this s tudy, constitutive parameters are conceived as stochastic fields in bo th space and time. Evaluation of phosphorus transport in a small strea m in Sweden indicates that the heterogeneity (covariance structure) of partitioning with respect to solute/particulate adsorption and bed re tention imposes significant effects on both statistically expected pre dictions and confidence intervals. Specifically, the temporal and spat ial variability found for the partition coefficient was sufficiently p ronounced to motivate that the coefficient is represented as an anisot ropic random field in space and time. An analytical solution to the in ternal turnover mechanisms indicates that the effects of system hetero geneity increase markedly with time.