Mechanical dispersion includes which of the following?

Mechanical dispersion refers to the process by which particles or solutes are spread or mixed in a fluid, typically due to the physical movement of the fluid itself. Advection is the primary mechanism through which this occurs, as it involves the transport of substances by the bulk motion of the fluid. In environmental contexts, such as groundwater or surface water systems, advection is crucial for understanding how contaminants move through water.

In contrast, the other options involve different mechanisms related to solute behavior in water. Adsorption and sorption refer to the processes by which particles adhere to the surfaces of solids, which can impact the concentration and movement of substances but do not describe the mechanical mixing of fluids. Permeability, on the other hand, describes the ability of a material (like soil or rock) to transmit fluids, which affects the flow of water but is not a direct mechanism of dispersion itself.

By understanding that mechanical dispersion, specifically in the context of fluid dynamics, primarily relates to the movement of solutes due to the flow of the fluid, it becomes evident why advection is the correct choice.