lowsalinity

Lowsalinity is a condition in which the salt concentration of a water body is unusually low relative to its typical salinity regime. Salinity is commonly reported in practical salinity units (PSU) or parts per thousand (ppt). In freshwater environments, salinity is near zero, while seawater averages about 35 PSU. Lowsalinity is most commonly discussed in estuarine and coastal systems, where brackish water results from the mixing of freshwater with seawater.

Causes of lowsalinity include natural and human factors. Natural drivers are increased freshwater input from rivers, rainfall, or snowmelt, as well as seasonal hydrological cycles. Tidal dynamics and oceanographic conditions can reduce the relative influence of seawater. Human activities such as damming, water withdrawals, and land-use changes that raise freshwater runoff or reduce seawater inflow can also shift salinity toward lower values. In some regions, climate variability or extreme weather events produce episodic lowsalinity events.

Ecological and biogeochemical consequences are variable and depend on the species present and the magnitude and duration of the salinity change. Many marine organisms have narrow osmoregulatory tolerances, so lowsalinity can stress or exclude some species while favoring others adapted to brackish conditions. Changes in salinity can alter microbial communities, nutrient cycling, primary production, and habitat quality. Lowsalinity is routinely monitored with conductivity sensors and CTD instruments to understand estuarine health, water resource management, and responses to climate-related hydrological shifts.