What is an estuary? An estuary is a partially enclosed body of water where two different bodies of water meet and mix (e.g. fresh water from rivers or streams and salt water from the ocean, or fresh water from rivers or streams and chemically distinct water of a large lake).

Transition zone between river environments and ocean environments Subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. The flow of both seawater and freshwater provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world.

Turbid waters Waters in estuaries are often turbid and brackish Turbidity is caused by stirred up sediment and the influx and withdrawal of organisms such as phytoplankton.

Two main challenges in an estuary Sedimentation – Can be problematic for phytoplankton if sustained, plankton need sunlight to survive, they do not get this if they are submerged in the sediment Osmoregulation – Osmoregulators Maintain a constant internal water/salt balance even though the environment is different. Includes freshwater fish, many marine fish, all terrestrial animals Osmoconformers Have internal osmolarity similar to that of the surroundings. Most marine invertebrates, some vertebrates, e.g. sharks

Freshwater fish tend to gain water and loose salt Marine fish tend to gain salt and loose water

Provide habitats for large number of species – fish nurseries (salmon, sea trout etc). Also feeding grounds for many birds. Primary producers are phytoplankton which feed on detritus in the water. Many species of bacteria live in the sediment of estuaries, this can have implications on other sediment dwelling species as they are in direct competition for resources (oxygen).

Common species found in British estuaries Many animal species are found in British estuaries, these include: arthrop0ds (crustaceans and insects) molluscs cnidarians Polychaetes Birds Echinoderms Many grass, phtyoplankton and seaweed species

Threats to estuaries 6o% of the worlds population live around estuaries and the coast– Why? 22/36 of the worlds biggest cities sit directly on estuaries. Human threats: Increased sedimentation due to soil erosion up stream Overfishing Drainage of wetlands Eutrophication from nitrates and phosphates – causes algal blooms etc – results in hypoxia and ultimately dead zones Pollutants including PCB’s plastics and heavy metals Over management and damming of areas for human purposes.

Task - Each of you have a journal article relating to estuaries in some form, the journals do not have abstracts. Your job is to write one, it should be between 100 – 200 words.

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