Four Main Groups of Estuaries

(1) Coastal plain estuaries were formed during last great rise in sea level when melting glaciers flooded river valleys.The river channel is usually less than 20 meters deep. Salt-marsh estuaries are part of coastal plain but contain predominantly salt water because they are not fed directly by river.

(2)Lagoons have less defined drainage network and are usually shallow and have raised ridge or sand barrier.

(3) Fjords are a major type of estuary formed when continental glaciers scoured out river valleys. Water in interior part of fjord can exceed 500 m in depth.

(4) Tectonic estuaries result from major geological events such as faulting, volcanic eruption, or landslides. The best know example of a tectonic estuary is San Francisco Bay.

Chemical components of fresh water vary, whereas salt water is fairly uniform. The variations in chemistry of river water produces differences in nutrient cycle of estuary.

*Silicon, iron, nitrogen, phosphorus come from river water.

*Sulfate and bicarbonates come from seawater.

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