Balancing the Ecosystem
The ecology of a clean broad requires a balance
In order to tip the balance away from a lake full of algae and towards clear water, we needed to help the little animals which eat algae. So, special sanctuary areas were created for them. The principal heroes of broads restoration are various species of Daphnia, otherwise known as 'water fleas'. They are a group of tiny crustaceans (related to crabs and lobsters), which filter the water they live in and eat the algae they find in it. They are actually attracted to wavelengths of light given off by algae. But they can't cope with the long strings of blue-green algae, which clog up their mouth parts, making them waste masses of time cleaning themselves up.
A fish-proof curtain gives the little guys a chance
While the Daphnia are hungrily munching the algae, young roach and other fish hungrily eat the Daphnia. So in order for the Daphnia to get a head start they need protection. 'Biomanipulation' is the name given to the technique of temporarily removing fish so that Daphnia can proliferate and eat the water clean. In Barton Broad, it was never going to be possible to biomanipulate the whole of the broad, since the river River Ant flows through it, and thousands of boats cross it every year. Instead, fish-free bays were created around the margins of the broad, isolating them from the main broad using specially designed fish-proof curtains which stop the fish. This novel design of curtain was piloted at Barton during the project. It is a flexible, plastic curtain, which can cope with seasonal and tidal changes in water level. It not does not damage boats if they accidentally collide with it, and since it does not stick up out of the water it doesn't intrude on the landscape. It has proved so successful that it is now being used in several other biomanipulation projects elsewhere in the Broads and Europe.
Instant fishing - with electricity!
The most effective method of fishing in these circumstances is to use an electric current to stun the fish temporarily. This technique made it possible to identify, count and measure them before they were put carefully into the water outside the curtain. The water within the fish-proof exclosures cleared soon after the electro-fishing, as Daphnia populations rocketed. By summer 2000, when, in the whole of the main broad, the Daphnia population was only 46 million, inside the fish-free zone it was 4,600 million.
Since the earliest days of this fish-proof curtain, the method of fixing it has been redesigned and the fishing exercise repeated in order to get rid of the fish who sneaked back under or round the curtain.
Plants are the key to this kind of restoration project. In order to stay in balance, the wildlife in the broad needs an underwater jungle. Healthy growth of plants provides refuges for the Daphnia where they can hide from fish during the day and venture out to graze at night - their nocturnal habits help them avoid being eaten.
In autumn 2000, divers doing plant surveys within the biomanipulated areas of the broad reported some growth of young seedlings including stonewort (Chara spp.), hornwort (Ceratophyllum), water starwort (Callitriche), Canadian pondweed (Elodea canadensis), yellow water lily (Nuphar lutea) and the true bulrush (Schoenoplectus lacustris) which used to dominate the broad. Five years on people have been astonished at the displays of flowering water crowfoot inside the fish-free areas and are beginning to see plants recolonising the margins of the whole broad.
