What fundamental physical characteristic of saltwater affects its movement in aquifers?

The movement of saltwater in aquifers is fundamentally influenced by its higher mineral content compared to freshwater. This higher mineral content increases the density of saltwater. Denser fluids tend to behave differently in terms of buoyancy and movement when in contact with less dense fluids, such as freshwater. In terms of hydrology, when saltwater enters an aquifer that is primarily composed of freshwater, it tends to sink beneath the freshwater due to its greater density. This principle is essential in the study of groundwater and aquifer behavior, particularly in coastal areas where saltwater intrusion can occur.

In contrast, while viscosity, cooling rates, and density relative to freshwater can all influence water movement in various contexts, the primary distinguishing feature that directly affects how saltwater interacts and moves within aquifers is its elevated mineral content, leading to an increased density that affects gravitational forces and hydrodynamics between different water types.