Brackvatten

Brackvatten, or brackish water, is water with salinity between freshwater and seawater. It is commonly defined as about 0.5 to 30 practical salinity units (psu). Salinity varies as freshwater from rivers mixes with seawater, and as evaporation, precipitation, tides, and human activities modify conditions. Brackvatten occurs in estuaries, coastal lagoons, deltas, and some inland lakes where mixing creates intermediate salinity.

Physical characteristics: Brackvatten typically shows denser layers and gradients in salinity, temperature, and oxygen. Turbidity and nutrient levels can be highly variable, and human activities such as damming or dredging can alter salinity regimes.

Biology: The communities are often adapted to variable salinity; many species are euryhaline. Inhabitants include estuarine fishes such as gobies and flounder, various crustaceans and mollusks, and aquatic plants like eelgrass.

Significance and threats: Brackvatten provide important ecosystem services such as fisheries, migratory habitat, and natural buffering against storms. They are vulnerable to climate change, altered river flows, pollution, eutrophication, and dredging, which can disrupt salinity balance and oxygen conditions.

Examples: In northern Europe, brackvatten form gradients in the Baltic Sea region where freshwater inflows meet saline waters; similar estuarine zones occur worldwide.