Permafrost

Carbon reservoir peatlands
All told, roughly a quarter of the Northern Hemisphere, especially in the Arctic, belongs to the permafrost zones. Within the permafrost zone, only approximately 15 million square kilometres are permanently frozen. Yet the Arctic is warming faster and more dramatically than any other region on Earth. In contrast, peatlands cover only 3 percent of the Earth’s surface, but sequester 25 percent of organic soil carbon; that’s twice the amount stored in all of the world’s forests. As such, both types of landscape are extremely important from a climatic standpoint. To more precisely gauge permafrost soils’ effects on the climate Katrin Kohnert gathers data on the natural gas exchange during her flights over research areas measuring up to 100,000 square kilometres. For the project “Airborne Measurements of Methane Fluxes” (AIRMETH) AWI engineers equipped the old DC3 with various types of equipment in the course of several-week-long preparations: sensors for measuring temperature, moisture, wind speed, and wind direction, are attached to the plane’s nose. Further, a system of pipes pumps external air from an opening in the plane’s roof and into a gas analyser, which can measure the concentrations of carbon dioxide, methane, and water vapour at high speeds. “At roughly 50 metres up, the measuring systems can accurately record the exchange processes between the surface and atmosphere,” Kohnert explains. In other words: only at this low altitude can they measure how much carbon dioxide is drawn from vegetation through photosynthesis on the one hand, and how much methane is released on the other. Katrin Kohnert’s task was to prepare the aerial campaign down to the last detail. “I take care of planning the flight route. And once we’re in the air, I have to make sure the pressure in the gas analyser remains stable; otherwise, the measurements are no good.”

Good news
For every research campaign, her team usually has four weeks on site, during which they overnight in group housing units with what Kohnert affectionately refers to as ‘the rustic charm of corrugated steel.‘ As team leader Torsten Sachs adds with a laugh, “You have to get along pretty well in order for it to work, especially if bad weather or technical problems force us to change the flight plan. After all, we’re not there on holiday.” For her doctoral dissertation, which she defended in late 2018, Kohnert integrated not only her field data, but also information from satellite imagery into the analysis. “I wanted to determine whether or not there are spatial patterns in the emissions, say, if lakes emit more methane,” she relates. She presented her findings as maps – pioneering work based on a painstaking calculation technique, and the results of which held their fair share of surprises for the members of the Working Group. “The initial outcomes show that, at least in Alaska, the soils aren’t emitting as much methane as the readings from the ground stations would seem to indicate,” says Kohnert. “And lakes and ponds, which were generally assumed to be ‘hot spots’, aren’t particularly active on a regional scale, either.” According to Torsten Sachs: “From a climate perspective, at least, that’s good news.” Sachs’ team is also measuring climate gas emissions in northern Germany – in the peatlands of Mecklenburg-Vorpommern, to be precise. Following German reunification, many hundred hectares of land that had previously been drained and intensively used for agriculture were restored, so that flora and fauna could once again grow and thrive there naturally – but also in order to reduce the high CO2 emissions produced by the use of drained wetland soils. The long-term goal is for wetlands to form once again on a total area of roughly 37,000 hectares. Here, too, the Potsdam-based efforts are measuring the climate effects of these land restoration efforts from the air – but, given the power lines and wind turbines in the region, they’re flying at 150 metres above ground using a motor glider from the Free University Berlin. In addition, together with colleagues in Rostock, they operate stationary measuring towers and are gathering additional soil data. What they’ve learned so far: though these efforts are beneficial in terms of plant and animal diversity, they don’t necessarily immediately produce positive climate effects: “When the Hütelmoor peatland on the Baltic coast near Rostock was flooded in 2009, the methane emissions increased 100-fold,” Sachs reports. “By 2011, they had dropped by roughly a third, but the level has remained fairly constant ever since.”

Emissions remain
In contrast, the researchers are still waiting for the methane emissions to drop substantially at the Zarnekow polder on the Peene River, whose dikes were dismantled in 2005; it didn’t become a CO2 sink until 2018, and the carbon dioxide emissions still remain far higher than predicted. “Apparently, the massive agriculture-based changes have very long-term impacts,” says Sachs. One potential explanation: methane-producing microorganisms (archaea), which break down the available biomaterial, are already thriving in the rewetted, once intensively fertilised soils, while their counterparts, the oxidisers, still need more time to establish themselves. Consequently, the climate experts suggest that, in future land restoration projects, the uppermost soil layers be removed before the land is flooded. “In the best-case scenario, this could significantly reduce the negative effects,” hopes Sachs. Even if many questions regarding the climate effects of wetlands and permafrost regions remain open, for the Potsdam-based team one thing is certain: when left alone, peatlands guarantee that little carbon dioxide or methane is released, but human activities can permanently destroy the biotope’s fragile equilibrium – which makes it all the more important that the potential risks and benefits of such activities be carefully considered in advance.