Salinity is a measurement of how much salt is present in water and distinguishes fresh water from brackish or salt water. We measure salinity in parts per thousand (ppt). For example, with one gram of salt to one thousand grams of water, the salinity is 1 ppt. Fresh water's salinity is 0-2 ppt and salt water salinity is an average of 35 ppt. The salinity of water can greatly influence the species present in that environment. Salinity is especially important in an estuarine system (such as Galveston Bay) where fresh and saltwater sources mix to create brackish water. Seasonal changes in salinity, mostly caused by rainfall or evaporation, attract different species to the area for living, breeding, or egg-laying. Some human activities can influence salinity levels in an estuarine system, such as the damning of rivers for municipal fresh water use.
The average salinity of Galveston bay is 29 ppt.
Artist boat students use a refractometer for measuring the salinity of water: