“They needed to make a design that offered a lot of room for natural dynamics and processes,” he says. “On the first day you will build it. But from the second day it’s in the hands of nature.”
Marker Wadden’s perimeter is, roughly, a rectangle, with one short and one long side providing an L-shaped, protective wall, built mostly of sand. One stretch — the 1.8 kilometres that is most exposed to the prevailing wind and waves — is made of stone.
The rest of the L shape takes the form of long and lonely white beaches with raised dunes behind them, providing protection for the seven low islands. Each of these consists of a sand ‘ring dyke’, or compartment, filled with mud. In all, it took 37.2 million tonnes of material dredged almost entirely from the lake floor. The first island was finished in 2016. A year later, a research programme began, carried out by a group of universities and research organizations, funded with about €6 million from a variety of sources. It is known as the Knowledge and Innovation Programme Marker Wadden (KIMA). Late last year, they presented their findings — but this is a young ecosystem, and their research has really only just begun (see go.nature.com/3mbz89t).
Built with mud
It takes around half an hour for the project’s boat to cross from Lelystad to Marker Wadden’s small marina, behind which are some austere wooden buildings, including a visitor centre and scientists’ dormitory. This is the human hub of the site, and the only island with tourist access.
High dunes flank one side of the settlement, and all that can be heard is the steady wash of waves, the tread of volunteers going about their tasks and birdsong. Paths radiate from the settlement along dykes, offering lonely vistas of pools, marshes and wildlife.
Posthoorn leads the way along one of these paths, flanked by beds of swaying reeds as high as people, which soon part to reveal mudflats covered mostly in a dark green plant known as marsh ragwort (Tephroseris palustris). It will put out yellow flowers in the spring “when the whole place will smell of honey”, says Posthoorn. Marsh ragwort is a pioneer plant — quick to take up residence on bare mud.