After fifty years of measurements, soil physicist Guido Bakema can state that Dutch peatlands have subsided an average of 35 centimeters. This process must be slowed. “Choices have to be made.”
In fifty years, the soil in Dutch peatlands has subsided by an average of 35 centimeters. “We know about it, but it’s a slow process, just like climate change. At some point, you’ll notice the consequences, and now we know exactly how fast that process happened,” says soil physicist Guido Bakema.
Subsidence in peatlands has major consequences: 9 percent of Dutch soil consists of peat, primarily in North Holland and South Holland, Utrecht, and in the northern part of Overijssel and Friesland. Measuring peat subsidence began in the 1960s when agricultural mechanization advanced. Horses were replaced by tractors. To be able to access the land with those heavy machines, the soil had to become drier. To achieve this, the water level was lowered.
For decades, it has been known that soil subsidence leads to damage to house foundations, not only in cities like Gouda in the Green Heart region, but also in Friesland. In recent years, the damage to the climate caused by carbon dioxide emissions has been added to this.
Peat soil has been formed over the centuries by slowly decomposing plant material. The plant remains, which store carbon, are only preserved by wet and oxygen-poor conditions. Lowering the water table allows oxygen to reach the plant remains. This process is called oxidation. Carbon dioxide is released, and the soil subsides. There are significant regional differences. In Hoenkoop (Utrecht), the subsidence was 10 centimeters in 50 years, and in Spannenburg (Overijssel) and Assendelft (North Holland) it was at least 85 centimeters. The differences are mainly caused by the extent to which the water level has been lowered and the water is pumped away. Until ten to twenty years ago, water boards lowered the water level even further when the ground level subsided. They’ve practically stopped doing that, says Bakema. “They know there’s no end in sight. If you keep doing that, in a hundred years, the peat in Friesland, for example, will be gone leaving you with the underlying layer, the sand.”
It’s been clear to politicians for several years now that a more rigorous approach is needed: wetting the peatlands to slow greenhouse gas emissions and stop house subsidence. Now we’re waiting for action, says Bakema, but he adds that it’s not easy. “What can be done with that wet land? What do you do with the farmers who are currently active there? Choices have to be made. There are plenty of ideas on this, such as a combination of nature and agriculture with lighter machinery, which allows you to preserve the grass and its roots, which store a lot of CO2.” Making the peatlands far too wet is also not good, says Bakema. “That causes methane emissions, which have an even greater effect on climate change than carbon dioxide. So we also need to measure the effect of rewetting. Yes, as far as I’m concerned, we’ll do that over the next fifty years.”
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