A transport pathway can be thought of as a transfer function (i.e., an operator), whose input is a mass flux rate and whose output is a mass flux rate:
The transport pathway operates on (i.e., delays, spreads, reduces, magnifies) incoming mass fluxes in order to produce a time history of outgoing mass fluxes from the pathway. In the absence of decay, transport pathways conserve the mass of contaminant within a system.
Note: Although it is
convenient to think of all pathways as transfer functions, this description is
not strictly mathematically accurate for Cell pathways that are part of a larger
Cell
net.
Physically, transport pathways represent the components of a system through which mass (e.g., contaminant species) can move and/or be stored. Typically, a pathway will represent all or part of an environmental component, such as an aquifer, stream, soil compartment, lake, or a portion of the atmosphere. You define the properties of the pathways, such as their geometry and which environmental media (e.g., water, air, soil) they contain.
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