Restoration Twitchiness
The UK’s Biodiversity Action Plan seeks the creation of 120hectatres of saline lagoon by 2015.The latest RSPB/MQR article in a series of six shows how the former clay workings at Cliffe Pools in Essex are a good example of how the aggegates related industries can help the UK reach its target and help preserve lagoon inhabitants such as the distinctive avocet.
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Saline lagoons are coastal water bodies that contain a mixture of sea water and freshwater. They are separated from the sea – partially or completely – by sandbanks, shingle or artificial structures and are a habitat under threat.
Full of brackish, saline or hyper-saline water, lagoons cover around 5,200hectatres in the UK with the largest being the Loch of Stennes in Scotland, which is in excess of 800hectares. The UK Government is keen to see more created.
The Biodiversity Action Plan calls for 120hectares to be created by 2015. But this is not an easy job. Their natural creation is inhibited by human coastal activities and the predictions are that new lagoons will not keep up with lagoon loss.
And if lagoons recede so do the population levels of their inhabitants. One such resident is the avocet with its black and white feathers and elegantly upturned bill. And as they were deemed extinct in 1840, to start to lose them again now would be negligent.
Today, virtually all the UK’s 600-800 breeding pairs nest on saline lagoons. One of the largest concentrations is to be found at Cliffe Pools in Kent, a series of lagoons on former Blue Circle clay pits next to the Thames.
After being abandoned in the ’70s, the diggings at Cliffe were initially filled with fresh water. However, the newly formed lagoons were a convenient place to put dredgings from the Thames. Large amounts of silt, gravel, sand and salt water were pumped in and, over the next 40 years, a series of saline lagoons was formed.
By the time the RSPB bought the site in 2001, it had developed into 110ha of nationally important habitat, accounting for just under 10% of England’s lagoons. Work to improve the site goes on through an agreement RSPB has with Westminster Dredging.
Westminster currently has planning permission to completely infill some of the remaining lagoons. The RSPB guarantees to take a certain volume of dredgings and it supports the granting of planning permission for the dumping dredgings into the other lagoons.
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Michael Ellison, warden at the Cliffe Pools reserve, says: “Most are pretty deep and saline lagoons are at their best when they are shallow – ideally no more than a metre deep.
The plan is to create a network of shallow lagoons, which are at most two and a half metres deep, but an average of less than one metre.
“The dredging process is absolutely key. In terms of bird management, the way the dredgings are put in and our relationship with Westminster is critical,” he says.
So, what environment does the avocet need?
The most-species rich lagoons have a salinity of between 20 and 35 parts per thousand and have a large edge to surface ratio. Shallow margins give avocets places to feed, while low islands provide nest sites.
They like to nest on bare mud close to the water and prefer small islands, which do not attract other birds such as black-headed gulls. Water levels may also have to be fine-tuned in order to provide enough shallow feeding area.
Constructed lagoons are usually built with sluices and weirs to control water levels. These are critical to successful management of tidal exchange. It is also needed to stop lagoons drying up in summer, flooding with fresh water in winter, and for management, such as flooding nesting islands to kill unwanted vegetation such as reeds.
The location of saline lagoons is crucial, as is the availability of sea and freshwater.
Otherwise, saline lagoons are relatively straightforward to create and can quickly become outstanding habitat, not just for avocets but a range of specialist species including crustaceans, shellfish, plants and insects. All that is needed is the right land.
So if you have an operation near the coast and would like to help the UK meet its target for saline lagoons visit the website below. Other lagoon sites created from quarrying in the UK include Killingholme in Humberside and Snettisham Pits in Norfolk.
