Saltholdighet

Saltholdighet, or salinity, is a property describing the concentration of dissolved salts in a solution, usually water. It is typically expressed as practical salinity units (PSU) or as parts per thousand (ppt, g of salt per kg of solution). In seawater, salinity is about 35 PSU (approximately 35 ppt), reflecting dominant ions such as sodium and chloride; freshwater rivers and rainfall dilute salinity and may vary from almost zero up to several tens of ppt in brackish waters. Salinity is measured by conductivity, with conversion to salinity using scales such as PSS-78; chemical analyses of chlorinity and ionic composition are also used. Salinity affects water density and osmotic pressure, influences marine circulation, weathering, and biogeochemistry.

Natural processes modulate salinity: evaporation increases salinity in closed basins like the Dead Sea or certain bays, while precipitation, river inflow, and ice melt reduce it; mixing with freshwater can homogenize salinity in estuaries and coastal zones.

In biology and agriculture, saltholdighet has ecological and practical implications: many organisms are adapted to specific salinity ranges; plants experience osmotic stress and ion toxicity at high salinity, reducing crop yields. Soil salinity management includes leaching with freshwater, improved drainage, and selecting salt-tolerant species or implementing desalination. In engineering and industry, salinity is relevant for water treatment, desalination processes, and food preservation.