In a Salt Wedge Estuary, which describes the salinity arrangement?

• A. Freshwater forms a wedge into the sea.
• B. Salinity is uniform throughout the estuary.
• C. Only occurs in tidal creeks.
• D. Saltwater intrudes into the river channel as a wedge from the sea, lying beneath the freshwater.

Answer: (D)

In a salt wedge estuary, density differences between seawater and river water drive a sharp separation of layers. Seawater is heavier, so it intrudes from the sea into the river channel along the bottom, forming a wedge that lies beneath the fresher water riding near the surface. This creates a distinct interface: salty water at depth, fresh water above, with the wedge pushing upstream when river discharge is low and retreating when it’s high. This arrangement—seawater moving in as a bottom wedge and beneath the freshwater—best describes the salinity pattern in a salt wedge estuary.