2023-08-18 06:00:00
The Frisian Wadden have suffered from the drought in recent years. Strangely enough, the rise in sea level also has consequences at the same time.
‘High water 6.30 pm’ is written on the chalkboard that hangs at the terrace of Yke-muoi. The idyllic tea house behind the dike in the small Moddergat, one of the northernmost villages in Friesland, attracts many mudflat hikers. Slippers are exchanged for high sneakers and here and there children run onto the dike.
Seagulls skim through the air towards the sea. It will take another eight hours before the water is at its highest once more. Enough time to walk towards Schiermonnikoog. The Wadden Island is clearly visible from the dike.
Jan Christiaan Kraster puts on diving boots. The tight-fitting footwear ensures that the experienced mudflat hiker does not get stuck in the sticky mud. He also retrieves a long, bright blue stick from his car. Other guides walk around with a yellow or green stick. Later it will become clear why.
The king too rich
The water has not yet completely receded and despite the soft ground, Kraster steps on firmly. “There are a few mussel beds further on,” he points out. “In the years that I have been coming here, I have seen them disappear a lot. This is partly due to the Japanese oyster. It has taken over the territory of the mussel. When I was little, I was a king if I found a nest of oysters. That almost never happened. Now you find them everywhere”. He points to the mother-of-pearl shells over which the mussels lie.
Another threat to mussels is the increasing drought. That may sound contradictory, drought and the sea, but it is indeed a problem in the Wadden area. Because normally water from the IJsselmeer is discharged into the sea, but not when it is very dry. Fresh water is then saved: it first goes to drinking water facilities and agriculture.
And that has consequences for life in the Wadden Sea. “Starfish cannot tolerate fresh water and they like to eat mussels,” says Martin Baptist, researcher at Wageningen University in the field of marine ecology. “If no fresh water is drained, the starfish have a much better chance of survival and therefore more mussels are eaten.”
Clams filter the water
In addition to mussels, cockles are also having a hard time, due to the drought and extreme temperatures. Not only in the summer there is great cockle mortality, low temperatures in winter are just as dangerous. Because cockles are in the top layer of the soil. If the temperature is too high or too low, they will not survive, and this is becoming increasingly common.
Those high temperatures, often in the form of heat waves, also cause extra evaporation, which increases the salt content of the water in the Wadden Sea. It will also become warmer on tidal flats, which is problematic for many organisms that live there. Like the cockle.
Clams are another source of food for birds, Baptist explains. “Moreover, they eat algae. As a result, they filter the water, as it were. That applies to all bivalves.”
Drowning Islands
Not only desiccation is a current problem in the Wadden Sea, at the same time the rise in sea level also has a major impact. Due to the melting of the ice caps, the sea level is rising and more water is flowing into the Wadden Sea. An important consequence of this: more sand is needed.
“The plates in the Wadden Sea consist largely of sand, the islands themselves were created by sand and the deposition of silt,” explains Baptist. “If there is more water, there must be more sand to ensure that the sandbars remain intact. In many areas, extra sand is sprayed onto the seabed off the coast or on beaches. That way the islands don’t drown.”
But according to the researcher, these sand nourishments are not a very sustainable choice. “If we remove sand elsewhere, it will disrupt the ecosystem there. But in the end we have to choose between intervening or flooding the islands. People opt for the former, so now it is a matter of looking at how this can be done as sustainably as possible.”
Only uncertainty is certain
The fact that sand moves is nothing new in itself, says Theo Gerkema, physical oceanographer at the Royal Netherlands Institute for Sea Research (Nioz). “Initially, the tide, with waves caused by strong winds and eroding of the bottom, causes displacements in the Wadden Sea,” he explains. “Erosion loosens sand, which is then carried away by the tide and wind-driven currents and deposited elsewhere. Take the Razende Bol. That sand plain is increasingly moving towards Texel and that is a natural process, caused by the tides and the waves.”
What is new are the consequences of the rise in sea level: this ensures that the current caused by the rising and flowing water is strengthened. “It is already almost unbelievable how much water flows into and out of the area every day,” says Gerkema. “That current transports a lot of sediment.”
The mud piles up
Wadloper Kraster sees it happening around him: the mudflats are constantly changing. “The only thing that is certain regarding the Wad is that it is uncertain.” He walks to a drier area and uses the long blue stick to draw the islands and the currents created by the tide. “You can already see the mud accumulating when I pull my stick through the mud. In principle, this also happens due to the current and the waves.”
Due to these constant changes, it is not always clear what the fairways look like. That is why guide Kraster always carries a long stick with him. “I don’t know exactly how deep that gully is and it’s not always clear how it has changed. It may just be that you are up to your hips in the water. I always put this blue stick in the water first, then I know how deep it is and I won’t be faced with any surprises.”
The stick also comes in handy now. When crossing from one sandbar to the other, the intervening water is still deeper than expected. “And of course it is a landmark,” adds Kraster. “Between all that gray of the mudflats, such a blue stick stands out.”
Already a guide at the age of fourteen
At the age of eight, Kraster was taken on his first trip through the Frisian nature reserve by his father. “When he had walked his first tour, he immediately fell in love and started training to become a guide. He also took me quite early. I guided my first tour when I was fourteen.” Watching nature grow and learning from it gives Kraster the most satisfaction when he roams over the tidal flats.
The wind picks up, here and there a drop of rain falls. “Since the first time I went out on the mudflats, I’ve seen a lot of changes,” says Kraster, raising the collar of his jacket. “Some plants are no longer there. Eelgrass, for example, disappeared long ago due to a seaweed disease as a result of the construction of the Afsluitdijk. You can still see the plant now and then, but it hardly ever happens.”
Four hours following the start of the tour, Kraster returns to the village behind the dike. The last bit of wading is tough. The ground is soft, it takes effort to ramble through the mud. Once on land, Kraster exchanges the dirty shoes for a clean pair of work boots and stores the stick in his car.
Read also:
The return of seagrass on the Wadden
Seagrass has largely disappeared from the Wadden Sea. But recovery is possible, say researchers following four years of experimenting with planting seeds at Griend.
1692422361
#Drought #sea #consequences #Wadden #area