If you’ve recently visited Belfast’s Window on Wildlife you might have noticed that the usual oasis of calm water stretching out towards Belfast Lough looks a little different … 
The most recent spell of dry weather, coupled with the lack of rainfall has meant that the water levels in the lagoon have dropped, 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. 

Where does the water in the Belfast WOW 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 Belfast WOW lagoon in summer?

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.

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 water line.

 Image credit: common terns, Joel Rock 

Why has the water at Belfast WOW 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?

At the moment, migrating waders such as godwits have been enjoying the available muds to forage for abundant invertebrate species and to fuel up before migrating. Whilst it might not look as pretty to some, currently the exposed wet mud bed means lots of invertebrates such as worms, snails, flies and beetles to eat.

Breeding seabirds including common terns and Arctic terns are currently nesting and raising their chicks on our purpose-built rafts. As they forage for food in the Lough, they should be unaffected by changes in the water levels in the lagoon.

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.

 Image credit: Black-tailed godwit, Stephen Maxwell

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 wildlife that uses this site. 

We’re currently gathering information to determine the best options for future management. We have placed data loggers into the lagoon and the Victoria Channel, to establish if there are any leaks, measure evaporation rates, and record the high tide levels in relation to the lagoon. We are also surveying the lagoon bed to map the shallowest and deepest areas and assessing the mud composition.

The options available which we are currently looking into are:

  • an intertidal exchange system which could bring saline water in from the Victoria channel
  • the possibly of bringing in processed water from the nearby Tillysburn water plant
  • holding more rainwater on site throughout the year
  • or installing a borehole on site which would allow us to access water beneath the surface

We will fully weigh up all the possible effects of each option, taking into consideration what impact - if any they may have on the existing wildlife that uses the lagoon.

The ideal solution would be one that gives us year around control of the lagoon water levels. This would allow us to let water out when needed, especially for the spring migration, with the knowledge that we will have a source of water to fill the lagoon in time for the breeding season.

When we’ve gathered enough information, we will be better informed to decide, with the help of expert hydrologists and ecologists, 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, it is possible we might experience a lengthy period with a dry lagoon if the weather continues. Last year, we experienced similar conditions on the reserve in May which led to dry conditions on and off over the summer months.

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.

 Image credit: View across the lagoon, Stephen Maxwell

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