Numerical Computations of Advective and Diffusive Transports of Chloride in Lake Erie, 1970

Abstract

This paper is concerned with a numerical simulation of lakewide advective and diffusive transports of conservative pollutants or nutrients, such as chloride, in Lake Erie. The study is a continuation of a hydrodynamic modeling experiment to compute water circulations throughout the 1970 shipping season, also in this issue, and makes use of ship observations of chloride distributions at approximately 4-wk intervals during 1970, together with estimates of river loadings for the same periods.The model equations are based on the time-dependent, mass-conserving advection–diffusion equation. A vertically mixed, one-layer, two-dimensional model is employed for spring and fall, whereas a two-layer model is used to simulate the stratified lake in summer. The equations are solved by finite-difference formulations on a horizontal grid with a mesh size of 6.67 km. Using time steps of 6 h, predictions are made of the change of chloride concentrations between pairs of cruises and the results are compared with observations.While the advective currents are derived from the previous hydrodynamic study, diffusion coefficients are estimated by comparing model results for a range of coefficients. The resulting numerical values compare favorably with findings of diffusion experiments in actual lake environments.