What does salinity refer to?

Salinity specifically refers to the concentration of salts dissolved in water, primarily sodium chloride, but it can also include other salts. It is an important factor in aquatic ecosystems, influencing the behavior of organisms and the chemical processes in the water. High salinity levels are typically found in oceans, while freshwater sources, like rivers and lakes, generally have low salinity. Understanding salinity is crucial in studies related to water quality, as it affects the density of water, the types of species that can thrive in a given habitat, and how various pollutants interact with the aquatic environment. The other options relate to different aspects of water chemistry and physics, but they do not define salinity itself. For instance, temperature impacts water density and species distribution but does not indicate salt concentration. Similarly, pressure and clarity pertain to different measurements and qualities of water.