Tide of destruction threatens lagoons

Man threatens a unique environment while nature afflicts the farmer's friend and Brussels sows confusion

Dotted along Britain's coastline are hundreds of brackish ponds and lakes where salt water from the sea mixes with fresh water from the land.

They are called saline lagoons. The words conjure pleasing images of warm, languid waters but, with British weather and their surroundings of sea walls, shingle, scrubby pastures and housing, there is nothing remotely lush or tropical about them.

For biologists, however, their sometimes murky waters and silted bottoms represent one of the most unusual and threatened types of habitat in Europe. A committee of government scientists and wildlife conservation groups has proposed rescue plans for the lagoons and13 other habitat types, along with 116 plant and animal species.

The salt concentrations in their water can vary widely. Gales and high tides can push in sea water, raising the salinity, then heavy rainfall can dilute it back down to near fresh water levels. There are some 40 plant and animal species found in Britain which are adapted to these difficult conditions, including insects, worms, molluscs and shrimps and two small species of sea anemone which are found nowhere else.

One of these, Ivell's sea anenome, has only ever been found at one place in the world - a small urbanised lagoon at Shoreham in West Sussex. It was first discovered there in 1973, found again 10 years later, but recent surveys have failed to uncover it; Ivell's may have become extinct.

Britain has about 300 lagoons, which cover only five square miles in total. By far the largest is the Fleet, behind the long shingle bank of Dorset's Chesil Beach.

In the natural state, new lagoons are constantly being formed while old ones disappear under the encroaching sea or are filled in by reeds and sediment, turning slowly into dry land. But along today's heavily managed coastline, a combination of sea walls and development gives new lagoons little chance of forming, while some existing ones have disappeared under buildings and car parks.

Other threats are pollution by farm fertilisers, drainage works which affect the fresh water- salt water balance and the rise in sea level caused by the very slow subsidence of the south-eastern part of the British Isles.

The Solent coastline in Hampshire has Britain's biggest concentration of saline lagoons, thanks mainly to the long- defunct salt industry. This created a mass of shallow ponds, salterns, in which evaporation turned sea water into concentrated brine. Hampshire County Council has purchased miles of this shore to protect it from development. It has also increased the lagoon area by digging out some ground behind the sea wall and flooding the depression with salt water.

The biodiversity committee's rescue plan calls for at least half a square mile of new saline lagoon to be created over the next 20 years, for this would only be enough to keep pace with projected losses. It advocates putting conservation measures on a national footing, which would cost about pounds 1.5m a year.