How does river runoff lower salinity in gulfs in humid climates?

In humid climates, river runoff acts as a primary source of fresh water that dilutes the saline waters of a gulf. As rivers discharge into these coastal features, the influx of fresh water lowers the overall concentration of dissolved salts, a process often referred to as freshening.12

The extent of this salinity reduction is influenced by the gulf's physical characteristics, such as its degree of isolation from the open ocean and the volume of river discharge. In many cases, the water becomes significantly fresher toward the head of the gulf, particularly during periods of high runoff, such as the spring thaw. This influx of fresh water creates a salinity gradient, where the water becomes increasingly brackish as it moves from the open sea toward the river mouth. By introducing large volumes of fresh water, river runoff effectively counteracts the evaporative processes that would otherwise increase salinity, thereby maintaining the distinct, lower-salinity environment characteristic of gulfs in humid regions.132