Two of the most prevalent ions in seawater are chloride and sodium. Together, they make up around 85 percent of all dissolved ions in the ocean. Other ions are found in very small concentrations. The concentration of salt in seawater (salinity) varies with temperature, evaporation, and precipitation.

The density of water increases as the salinity increases. The density of seawater (salinity greater than 24.7) increases as temperature decreases at all temperatures above the freezing point. Between 4°C and the freezing point, the density of pure water decreases as temperature decreases.

Salinity levels are important for two reasons. First, along with temperature, they directly affect seawater density (salty water is denser than freshwater) and therefore the circulation of ocean currents from the tropics to the poles. Measuring salinity is one way to probe the water cycle in greater detail.

Primary salinity is caused by natural processes such the accumulation of salt from rainfall over many thousands of years or from the weathering of rocks. The small amounts of salt brought by the rain can build up in soils over time (especially clayey soils), and can also move into the groundwater.

Treatment

1. avoiding over-irrigation by monitoring soil moisture to work out water requirements.
2. good crop selection such as using deep-rooted plants to maximise water extraction.
3. minimising fallow periods using crop rotations and break crops.
4. avoiding deep ripping and overtillage to minimise infiltration of water.

Salinity is usually expressed in parts per thousand (ppt) or ‰. Fresh water has a salinity of 0.5 ppt or less. Estuaries can have varying salinity levels throughout their length and can range from 0.5-30 ppt depending on their proximity to river inflows or the ocean. The average salinity of ocean water is 35 ppt.

Evaporation of ocean water and formation of sea ice both increase the salinity of the ocean. However these “salinity raising” factors are continually counterbalanced by processes that decrease salinity such as the continuous input of fresh water from rivers, precipitation of rain and snow, and melting of ice.

Desalination is most often considered to be the process of removing salts from water. There are several methods of desalination; however, this Primefact is focused on ‘reverse osmosis’ desalination. The process of desalination does not always completely remove all salts from the water.

Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water.

Salinity is the measure of the amount of dissolved salts in water. It is usually expressed in parts per thousand (ppt) or percentage (%). Freshwater from rivers has a salinity value of 0.5ppt or less. Salinity is often derived from electrical conductivity (EC) measurement.

Salinity is the amount of salt in grams present in 1000 grams of water.

Most of the ocean has a salinity of between 34 ppt and 36 ppt. Some properties of water are changed by having salt in it: Salt makes seawater more dense than freshwater.

For humans, that magic number is 9. That’s the salinity, or the weight in grams of salt dissolved in 1,000 grams (35.27 ounces) of water, of human blood [source: Ocean Health]. This means that every 1,000 grams of fluid contains 9 grams (0.3 ounces) of salt and 991 grams (35 ounces) of water.

If there’s too high a concentration of salt coming in, the cells force out extra water to maintain balance, basically wringing themselves out. They stop functioning, you stop functioning. This is called death.