How is estuary salinity typically zoned from riverine to marine ends?

• A. Riverine, with low salinity near the river mouth; brackish mid-zones; marine end with higher salinity.
• B. Brackish water dominates the entire estuary with uniform salinity.
• C. Marine end has the lowest salinity while the river end is freshwater.
• D. Freshwater throughout with no salinity gradient.

Answer: (A)