Estuarine

Estuarine describes environments at the interface between rivers and the sea. An estuary is a partially enclosed coastal body of water where freshwater from rivers and streams mixes with saltwater from the ocean. Estuaries are typically shallow and dynamic, with water movement driven by tides, river discharge, wind, and the shape of the coastline and seabed. Salinity in estuaries varies spatially and seasonally, creating gradients from nearly freshwater upstream to marine conditions near the mouth. Depending on flow and geometry, estuaries can be well mixed, partially mixed, or stratified.

Ecologically, estuaries are among the most productive natural habitats. Nutrients carried by rivers fuel high primary production, and the mixing zone supports abundant plankton, invertebrates, and fish. Estuaries function as important nursery and feeding grounds for many species, including commercially important fish and crustaceans. Vegetation such as salt marshes, mangroves, and seagrasses often stabilizes shores, improves water quality, and provides habitat for wildlife.

Geographically, estuaries form at river mouths, in drowned river valleys, and in other coastal configurations where sediment delivery interacts with rising or fluctuating sea levels. They are shaped by tidal ranges, sediment supply, and coastal geomorphology, and occur worldwide in a variety of climatic settings.

Human impacts on estuarine systems are common and varied. Pollution, sedimentation changes, damming and water diversions, dredging, land reclamation, and climate change can alter salinity regimes, turbidity, and habitat structure. Restoration and management efforts emphasize watershed protection, habitat restoration, pollution control, sustainable fisheries, and adaptation to sea level rise, aiming to preserve the ecological services estuaries provide.