In a Salt Wedge Estuary, the interface between saltwater and freshwater is typically:

• A. Saltwater above freshwater near the mouth.
• B. A completely mixed layer with no stratification.
• C. A dry estuary with no water.
• D. An interface where saltwater lies beneath freshwater near the mouth.

Answer: (D)

In this estuary type, the key idea is density differences between freshwater and seawater creating a layered system. Saltwater is denser than freshwater, so as the river water pushes toward the sea, the lighter freshwater stays on top while the denser saltwater moves in along the bottom. This forms a sharp, wedge-shaped interface that sits beneath the freshwater near the mouth and extends upstream along the riverbed. That’s why describing the interface as saltwater lying beneath freshwater near the mouth is the best answer. It would not be a completely mixed layer, nor would saltwater be on top, and the water isn’t dry at all.