brackishwater

Brackish water is water whose salinity is between freshwater and seawater, typically about 0.5 to 30 practical salinity units (psu), or roughly 0.5 to 30 parts per thousand. It occurs wherever freshwater mixes with seawater, such as in estuaries, coastal lagoons, mangrove swamps, and certain groundwater or brackish aquifer systems.

Salinity in brackish environments is variable and influenced by tides, rainfall, river discharge, evaporation, and seasonal changes. This fluctuation creates dynamic habitats with physical and chemical conditions that differ from both freshwater and marine systems.

Ecology in brackish waters favors euryhaline species capable of tolerating wide salinity ranges. These environments often support productive communities and serve as nurseries for many fish, crustaceans, and waterbirds. Nutrient inputs from land can enhance productivity, but pollution and sedimentation can degrade habitats and alter species composition.

Human use and management of brackish water include aquaculture (such as shrimp and certain fish species raised in brackish ponds), irrigation in coastal zones, and the treatment or desalination of brackish groundwater for drinking and municipal supplies. Compared with seawater, brackish water is generally cheaper to desalinate, though operations require careful management of salinity, chemistry, and ecosystem impacts to maintain environmental health.

Environmental challenges include salinity intrusion from sea level rise and groundwater extraction, pollution from agricultural and urban sources, and habitat loss due to development. Maintaining the ecological integrity of brackish systems typically involves integrated coastal management and monitoring of salinity, sediment, and nutrient loads.