The Dee Estuary
Here are just some of the reasons the Dee Estuary is special:
- The Dee Estuary is home to at least 120,000 wetland birds each winter which is the 7th highest overwintering population on an estuary in the UK.
- It is an internationally important location for seven species: shelduck, pintail, oystercatcher, knot, dunlin, black-tailed godwit, and redshank.
- A nationally important location for 13 more species including curlew, ruff, and lapwing.
- The Dee Estuary supports 70+ breeding birds, 23 mammal species, 24 butterflies and over 200 plant species (including five orchids).
What is an estuary?
An estuary is an inlet within the coastline where saltwater from the sea and fresh water from the land mix. Rather than geographical boundaries, the beginning and end of estuaries are determined by salinity, how much salt is in the water.
These habitats are highly productive and biodiverse due to their transitional nature. Because they connect to the sea, estuaries are tidal. When the tide comes in, it introduces large volumes of salt water into the estuary twice a day where it mixes with fresh water flowing in from the land. The result is brackish water – water that is saltier than fresh water, but less salty than seawater. This creates many unique habitats found nowhere else.
The rivers and sea deposit sediments within the inlet. This melting pot of water and nutrient-rich sediment creates one of the most productive ecosystems on the planet.
On the periphery of an estuary these sediments enable flora to thrive. The first of these is saltmarsh which is submerged by the incoming tide twice a day for many hours. These plants have evolved to survive the salt water and thrive in these conditions.
Further up away from the incoming tide are the reed beds. These areas do not become submerged at high tide, however small amounts of salt water may filter through them so they can tolerate brackish water.
Towards the middle of the estuary the mudflat created by the sediment is home to an array of fauna including shellfish, crustaceans, worms and much more.
Estuaries have a wealth of fauna because of the nutrient rich habitats but relatively low diversity because of the variability of salinity. Another challenge for the flora and fauna is the twice daily loss of water as the tide goes out. The most vulnerable residents such as invertebrates need to avoid drying out so most burrow into the sediment until the next high tide when they can reemerge to feed. This cycle is what attracts the large number of birds to the estuary.
During high tide the estuary bursts with life of all shapes and sizes from phytoplankton and zooplankton to grey and common seals.
