About Estuaries

Estuaries are the interface between land and sea: semi-closed regions where salt and freshwater mix, leading to a unique community of plants and animals.  An estuary can take many forms that are primarily dependent on its mode of formation( rising sea level, tectonic activity, receding glaciers, or shifting substrate) and water circulation ( tidal influence, topography, and freshwater out flow). However, high productivity, sediment deposition, varying salinity, and high biodiversity are a few traits most estuaries share. In certain areas, such as southern California,  some estuaries may also be referred to as lagoons or bays because low annual rainfall brings in very little freshwater input. 

Estuaries can be subdivided into further habitat types: shallow subtidal, tidal sand or mudflats, salt march, tidal creeks, and the upland transition zone.  Shallow subtidal habitats are submerged but are rarely deeper than light penetration. Mudflats are intertidal habitats that do not support any vascular vegetation. Salt marshes are tidally flushed low lying areas, bordering the estuary supporting salt tolerant plant species. Tidal creeks are streams driven by tidal flow. These areas are usually slow moving and further protected from physical forces. The upland transition zone, also known as riparian habitat, is where the aquatic and terrestrial habitats merge.