77% of Dutch wetlands (bogs, marshes) have been drained, mainly for agriculture and cattle breeding. This is a problem, as wetlands provide clean water, prevent flooding and store a lot of carbon, among other things. About 10 years ago, a number of Frisian farmers took part in an experiment that tried to reverse the effects of drainage, such as a decline in biodiversity, while allowing cows to continue grazing there. Ecologist Tom Heuts: ‘The experiments included tubes with water running through a field, or narrow ditches. Anything to try to get the underground water level up.'
Vegetation
The water rose to 35-60 centimetres below the surface during summer, but the ecologist's research shows that it did nothing else. Heuts: ‘We investigated whether vegetation that used to grow there would grow back because of the raised groundwater level. We also looked at whether the balance of nutrients in the soil, such as phosphate contained in fertilisers, improved.' This turned out not to be the case. 'We tried to get the water up to a level so that it didn't bother the farmer: they could still drive over the land with their tractor and the cows didn't sink into the grass. But we saw that biodiversity and soil quality did not improve.'
Plants on peatland
So what does help? Heuts: ‘A little bit of rewetting doesn't work, we need to go further to restore the wetlands and increase biodiversity. We need to do that together with the farmers: rewetting only parts of their land can probably also help. But these cautious measures are not enough.'
Previous research by Radboud University has shown that certain plants grow very well on wetted peat. An additional advantage is that they remove pollutants from the water and can be used as insulation material.