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Wet bogs without harming the climate

The Earth’s wetlands are vast reservoirs of greenhouse gas, just beyond oceans and forests. Although they cover only one percent of the earth’s surface, they store 20 percent of the carbon that ecosystems bind worldwide. A research team led by Ralph JM Temmink from the University of Utrecht calculated this in a extensive study.

But wetlands have been drained for centuries – until today. “Globally, around one percent of these ecosystems are lost to human intervention every year,” the researchers write. “The carbon dioxide released as a result accounts for about five percent of all man-made carbon dioxide emissions annually.” When a bog has dried up, atmospheric oxygen gets into the deeper peat layer. There it combines with the carbon that has accumulated over centuries to form climate-damaging carbon dioxide.

In Germany, seven percent of agricultural land was once moorland. Today, they account for 37 percent of agricultural carbon dioxide emissions – or around 7.5 percent of all German greenhouse gas emissions. The only antidote to stopping this release is to rewett the once drained moorland. Otherwise Germany will not be able to achieve its climate goals. But it is not advisable to simply fill in the drainage ditches or direct water onto the former moorland.

If you simply increased the water level on a former moor area, it would take 50 years or more for a real moor to form again, write the two researchers Dominik Zak and Robert J. McInnes from the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin in a recent publication. While the emissions from the lack of oxygen would stop pretty much immediately, methane gas is produced instead. This is what bacteria form when the peat soil is suddenly cut off from atmospheric oxygen by the water. Although methane is shorter-lived in the atmosphere than carbon dioxide, it is at least 25 times more effective on the climate. But that’s exactly what humanity doesn’t need right now.

In addition, this method also releases plenty of nutrients, as Zak explains. Because without water, the peat soil decomposed over the decades of agricultural cultivation. “If water hits it, a shallow lake is initially formed and the phosphorus bound in the soil is released,” says Zak. “The phosphorus concentrations of such dammed moor areas are 100 to 1000 times higher than in near-natural moors.” However, such amounts of nutrients can get into neighboring ecosystems and change them. In Denmark, these quick and cheap complete floodings have now been stopped for this reason.

However, if one took more time with the rewetting and slowly increased the water level over 10 to 15 years, it could be possible to avoid the negative climate and environmental effects of the quick-and-dirty method. “Under such conditions, these areas can continue to be used as grass or pastureland during the growing season, with even higher water levels only in the winter half-year, which overall reduces mineralization in the soil,” explains Zak. After about ten years, waterlogging can then be permitted all year round. Only from then on would the real bog growth begin.

A quickly effective but also quite expensive alternative would be to remove the top layer of the old peat soil before it becomes waterlogged. “In the top 20 to 50 centimeters, a large part of the phosphorus and other substances that pollute water is present in chemically mobile form,” says Zak. This method is particularly suitable where the groundwater is high. After that, the drainage ditches could be closed with part of the removed soil so that the water level would slowly rise again. In this way, the moor-typical vegetation develops within just a few years, as the researcher was able to demonstrate on experimental areas some time ago. In addition, methane emissions are reduced by a hundredfold.

However, Zak points out that none of these methods are a panacea. In order to decide how a former bog can be re-saturated with water, one must always take into account the nature of the terrain, area size, soil degradation, runoff, water table and current land use.

Politicians now also know that moors are immensely important for climate protection. On August 31, 2022, Federal Environment Minister Steffi Lemke did not choose a moor area for nothing – the Möllmer Seewiesen near Oranienburg – to present her design for the Action program for natural climate protection to introduce. It is the concretization of the 2019 adopted climate protection program 2030. This also includes measures from the federal-state target agreement of 2021 peat soil protection a. According to this, greenhouse gas emissions from peatlands are to be reduced by five million tonnes of carbon dioxide equivalents each year.

However, the renaturation of moors will probably not take place without conflicts. After all, the farmers want to continue to work on these areas. They would have to adapt to a new way of using the land, paludiculture, swamp farming. Reeds, cattails or peat moss would then be the new crops that they could market as building materials. The areas could also be built over with solar systems. However, it is certain that not all wetlands will be rewetted. For example, no one will want to dismantle Munich Airport, for which more than 1,600 hectares of moor were once drained. And elsewhere, settlements were built on moorland. Even climate change itself could have some watering plans nullify: Bogs also suffer during periods of drought lack of water how many rivers.

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