Hypersalinity

Hypersalinity refers to water bodies whose salt concentration significantly exceeds that of normal seawater (about 35 practical salinity units, PSU). It is a relative term without a single universal cutoff; many studies describe waters with salinities above 40–50 PSU as hypersaline. Such conditions occur naturally or through human activities and alter the physical, chemical, and biological properties of an aquatic system.

Hypersaline environments form where evaporation exceeds freshwater input, in enclosed basins, salt pans, coastal lagoons with restricted exchange, and some groundwater or industrial brines. Climate variations that increase temperature or reduce precipitation and anthropogenic water diversion can intensify salinization. The ionic composition may shift, with high concentrations of sodium, chloride and other dissolved salts, increasing density and lowering freezing point and gas solubility.

Biologically, hypersalinity limits biodiversity but supports specialized communities. Halophilic and halotolerant microorganisms (including many Archaea and bacteria), salt-adapted algae such as Dunaliella, and invertebrates like brine shrimp dominate. Microbial mats and stromatolite-like structures are common, and metabolic processes in these systems drive distinct biogeochemical cycles.

Human relevance includes traditional and industrial salt production, impacts on water resources, challenges for desalination and wastewater management, and ecological consequences when salinity changes alter habitat. Monitoring uses salinity units, total dissolved solids and ionic analysis to track changes and guide management in sensitive or economically important hypersaline systems.