ESTUARINE ENVIRONMENTS

The transition zones between rivers and the ocean. Rivers broaden within estuaries where tides operate in diurnal cycles, mixing saline water and fresh water. Estuarine environments are very dynamic, being continually modified by erosion and deposition in the short term and in the long term by, for example, sea-level changes. Estuaries are usually characterised by a distinct ocean inlet, which defines the point of entry of incoming tides. The Severn Estuary, UK, and the Bay of Fundy, Nova Scotia, Canada, have the highest tidal ranges in the world caused primarily by topographic factors, especially their funnel-like shape. Estuarine environments exhibit steep sedimentary, salinity, hydrochemical, hydrophysical, and ecological gradients over a relatively short distance. Water circulation and fluctuating salinity maintain highly productive ecosystems at a variety of scales. Estuarine plant assemblages (ranging from microscopic algae to sea grasses) provide abundant food and shelter to an equally productive and diverse fauna. Many estuarine ecosystems are strictly protected and monitored to ensure that conflicting usage by fishing and shipping, for example, are not detrimental to the ecosystem. Estuaries are nevertheless often the sites of high-level marine pollution.

[See alsoaquatic environment, brackish water, coastal zone management, mangrove, saltmarsh]