The outside spaces at Belfast’s Window on Wildlife reserve re-opened to the public at the end of May, but visitors to the hides that overlook the freshwater lagoon at WOW will have noticed that the usual oasis of calm water stretching out towards Belfast lough – looks a little different.

With the Met Office reporting that all parts of the UK exceeded spring sunshine records, this coupled with the lack of rainfall has meant that the water levels in the lagoon have dropped dramatically, exposing more mud than would be usual for this time of year.

Belfast Window on Wildlife warden Chris Sturgeon explains more about the effects of these natural processes on the birds that are breeding, feeding and roosting at the Belfast reserve:

 Credit: Met office

Where does the water in the lagoon come from?

Despite being next to Belfast Lough, the lagoon isn’t tidal, it’s actually fed solely by rainwater.

Which birds are attracted to the lagoon in spring and summer?

 Common tern. Credit: Stephen Maxwell

In spring, flocks of black-tailed godwits can be seen on the lagoon. They rest and feed on invertebrates such as flies, worms and beetles before heading north to Iceland to breed. Other birds such as moorhens, coots and mallards also use the site to breed. Birds which forage on the mudflats along Belfast Lough such as oystercatchers, rest here when the mudflats are covered at high tide. Above the waters you can spot swifts and swallows snatching up the flies which swarm above the waters.

Over summer, colonies of breeding common and Arctic terns use the floating tern rafts and surrounding shore areas to nest and raise their young. They forage for food in the lough, and can be seen gliding alongside passing ships, diving for fish that are churned up in the wake waters.

Why has the water dried up?

As the lagoon is fed purely by rainwater, it’s natural that long periods of dry weather mean a higher rate of evaporation and as a result more of the mud bed is exposed.

Does this have an impact on the birds here?

 Black-tailed godwit. Credit: Brian Douglas

At the moment, waders which migrate, such as godwits, dunlins, knots and the odd rarity such as a long-billed dowitcher which was spotted last week, have been enjoying the available muds to forage for abundant invertebrate species and to fuel up before migrating North. Whilst it might not look pretty, currently the exposed wet mud bed means lots of invertebrates such as worms, snails, flies and beetles to eat.

Breeding seabirds including black-headed gulls, common terns and Arctic terns have started to move into the site. Whilst it is still relatively early in the season, we expect that both gulls and terns should be able to successfully use both rafts and shore areas this year to breed and raise their young. Last year we had over 700 common terns nesting at the reserve.

Where the lagoon starts to dry at the edges, some plants will grow such as celery-leaved buttercup, which produces lots of seeds, as the lagoon fills up again this will provide a great food source for teals and wigeons when they return in the autumn.

However, there is a risk that if these dry conditions continue some species might be impacted. Later in the summer birds such as dunlins and redshanks that depend on the muddy waters edge habitat, where most of their food can be found, will move on elsewhere if this isn’t available. Lack of water and wet mud will cause invertebrate species to decline, which will mean less available food at the site. The good news is that this is unlikely to have a long-term impact as invertebrate species are quick to bounce back once the conditions improve.

What can we do about this?

With increasingly unpredictable weather patterns, we are working to find a long-term solution to make the lagoon more resilient to these changes and able to support the species that use this site. 

We’re currently gathering information to determine the best options for future management. This includes measuring water heights and evaporation rates in the lagoon, surveying the lagoon bed to map the shallowest and deepest areas and assessing the mud composition. When we’ve gathered enough information, we will be better informed to decide, with the help of expert hydrologists, how we might successfully manage the water levels here in the future.

When will the water return?

This will depend on our rate of rainfall over the coming weeks and months, it is possible we might experience a lengthy period with a dry lagoon if the weather continues. In 2018 we experienced similar conditions on the reserve in May which led to dry conditions at the lagoon into early autumn.

At the moment the mud is fresh, meaning that there is still quite a bit of moisture and if it rains, it will not take long to fill it up. However, if it dries out further and we start to see cracks appearing in the mud then we will need some torrential rainfall before we will start to see water levels rise. That said, if we get one of our famous Northern Ireland summers, the lagoon could soon be filled with water.

 Belfast WOW Lagoon. Credit: Stephen Maxwell

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