Estuary

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An estuary is a partially enclosed coastal body of brackish water where freshwater from rivers or streams meets and mixes with saltwater from the open sea. Estuaries form transition zones between riverine and marine environments and are classified as ecotones, areas where different ecosystems overlap. They are influenced by both marine processes (such as tides, waves, and saline water intrusion) and fluvial processes (including freshwater flow and sediment input). The mixing of seawater and freshwater provides high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. Most existing estuaries originated during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries can be classified using four fundamental criteria. These include salinity distribution, geomorphology, water circulation and vertical stratification...

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