Which statement best describes how abiotic factors differ in an estuary
and a river? *
Unlike a river, an estuary has changing flow rates.

Unlike a river, an estuary has changing salt levels.

Unlike a river, an estuary has changing water quality.

Unlike a river, an estuary has changing sediment load.

An estuary has changing salt levels  

Explanation:

A river is a large stream of water often winding from a source from a higher elevation flowing out to the sea. An estuary is the area where the river and the tides of the ocean come together.

The salinity of the estuary will depend on many factors and can change in time. First factor is the location of the estuary, these may be positioned where there is a varied amount of fresh water flowing in and the tides may or may not freely flow in and out.

substitution is the answer in this case