Estuary

An estuary is a coastal body of water where river freshwater mixes with seawater, usually under tidal influence. Its salinity and circulation vary with tides, river flow, and location.

Tidal prism: The volume of water entering or leaving an estuary between high and low tide. It measures the tidal exchange that drives circulation through an estuary.
Tide: The periodic rise and fall of sea level caused mainly by the Moon's and Sun's gravity. Tidal sea-level changes influence water exchange and mixing at an estuary's mouth.
Estuarine ecology: The study of organisms and ecological interactions in estuaries. Changing salinity, tides, and nutrients create distinctive estuarine communities.
Delta: A landform of deposited river sediment at a river mouth, often divided by branching channels. A delta is a sediment-built landform; an estuary is defined by mixed coastal waters.
Estuarine circulation: A circulation pattern in which surface and deeper water move in different directions along an estuary. Freshwater and seawater often form a two-layer flow within estuaries.
River discharge: The volume of water flowing through a river channel per unit of time. Changes in river discharge alter estuarine salinity, circulation, and sediment delivery.
Salt marsh: A coastal wetland regularly flooded by tides and dominated by salt-tolerant plants. Salt marshes are common estuarine habitats that shelter wildlife and retain sediment.
Lagoon: A shallow coastal water body separated from the sea by a barrier such as a reef or sandbar. A lagoon may exchange with the sea through inlets without receiving substantial river flow.
Salinity gradient: A change in salt concentration across distance or depth in a body of water. Mixing creates distinctive salinity patterns from river mouths toward the sea.
Salinity: The concentration of dissolved salts in water. Salinity distinguishes river water from seawater and shapes estuarine density.

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