ABSTRACT
This chapter develops simplified steady state and time variable solutions to the reaction and transport equations. Compart mentalization is a popular assumption in fate and transport modeling because the completely-mixed assumption reduces the set of partial differential equation to one of ordinary differential equations. Water can be stored within lakes or rivers by a change in elevation or stage. Inflows and outflows should be gaged or measured over the period of investigation. The transport of toxic chemicals in water principally depends on two phenomena: advection and dispersion. Chemical and thermal stratification serve to limit vertical mixing in lakes, and the eddy diffusivity is usually observed to be a minimum at the thermocline. Compartmentalization refers to the segmentation of model ecosystems into various "completely-mixed" boxes of known volume and interchange. Estuarine circulation is truly a two-dimensional problem involving a stratified surface layer of freshwater and a saline layer near the bottom.
