#Extreme #drought #knocks #peat #longer #expected
Peatlands are masters of carbon storage. But due to the increasingly frequent periods of extreme drought, this storage is in danger, Nijmegen researchers show.
Rob BuiterJanuary 18, 2024, 11:17 AM
The blessings of peat are difficult to overestimate, if you ask the Nijmegen biologist Bjorn Robroek. “For example, all the peat in the world stores 500 gigatons of carbon. So that’s 500 billion tons! If you consider that peat soils only cover 3 percent of the land surface, then peat is relatively the most important storage of carbon on land worldwide,” says Robroek.
But that storage is in danger, researchers from Robroek’s group say in the latest issue of the journal of the British Academy of Sciences. For an experiment, they brought a large number of containers with peat moss plants to a laboratory at Radboud University in Nijmegen. There they made different mixes of two types of peat moss in a large number of buckets, from one type entirely, via 1 in 3, fifty-fifty and 3 in 1 to completely the other type. After an artificial summer under special lamps, the researchers then exposed these buckets to different drought regimes. Using special hoods, they recorded how much CO2 or methane was absorbed by the moss in the containers during the experiment or how much escaped from the containers. Methane is also a molecule with carbon in it (CH4) and is also a very strong greenhouse gas.
Before the start of the experiment, the researchers saw that all containers with peat moss plants absorbed CO2; proof that the plants were healthy and growing. If the researchers set the ‘groundwater’ in their experimental tanks much lower, this growth was even stimulated somewhat. “A little bit of drought every now and then is good for peat moss,” concludes Robroek.
But when the researchers left some of the containers very dry for two weeks halfway through the experiment, the system’s absorption of CO2 completely collapsed. And even worse: when the containers were placed under the normal amount of water again after about three weeks, the absorption of CO2 in those previously driest containers barely started. In the tanks that had only been allowed to dry slightly, life continued as if nothing had happened after the groundwater returned.
‘Vault’ for safe storage
When Robroek translates the results of his experiment from the lab to a nature reserve, for example in De Peel, his picture is bleak. “After periods of extreme drought, peat apparently takes a big hit. It will then no longer absorb carbon for a long time and will even emit carbon. And those periods of extreme drought are becoming more and more common. This jeopardizes the important role of peatlands as a ‘safe’ for the safe storage of carbon,” says Robroek.
The blow that natural peat areas receive from extreme drought is in addition to the effects of desiccation as seen in the so-called peat meadow areas. These are old peatlands where, in most cases, grass now grows to feed cows. Because the groundwater level under the peat meadows is kept artificially low for the cows and agricultural machinery, the peat dries out permanently. Bacteria then turn it into CO2, with the net result that the soil sinks and CO2 emissions are boosted. Estimates by peat researchers assume that an average Dutch pasture in a peat meadow area, where the groundwater level is lowered in the summer, releases as much CO2 into the air per hectare per year as a middle class car that drives 135,000 kilometers. In the meantime, the ground is also sinking up to a centimeter per year.
“It’s blow after blow,” Robroek agrees. “Not only are we suffering from increasingly frequent periods of extreme heat and drought, in recent months we have seen that the opposite, flooding, can also occur more often. And then you need healthy peat areas to absorb those water peaks. A healthy peat area is a great sponge that can hold a lot of water, and then slowly release it to the environment when it becomes drier. But instead of healthy peat areas, we now have floodplains along the rivers where mainly grass grows and where hardly any water is retained.”
Emits marsh gas
The rewetting of nature reserves, which Robroek is now calling for, raises concerns among some about the possible emissions of methane, or swamp gas. That is not right, the Nijmegen experiments show. “Methane is indeed produced under wet conditions, but our measurements show that on balance, much more greenhouse gas is captured in wet peat moss systems in the form of CO2 than is released into the air as methane,” says Robroek, “even if you take into account the fact that methane is a much more powerful greenhouse gas than CO2.”
In the experiment, Robroek also looked at whether additional diversity in the peat makes the system more resilient. “That ‘diversity’ was of course somewhat limited, with different mixes of only two types of peat moss,” he acknowledges, “but the first signals were clear. Regardless of the mix of one type of peat moss or another, the effects of extreme drought were almost equally disastrous in all containers.”
Research in other ecosystems shows that, for example, a grassland or a forest becomes more resilient to ecological blows when there is more diversity in the system. Robroek thinks that this diversity will not save us when it comes to making peat resilient to extreme drought. “There is actually only one good solution, and that is to ensure that the peat does not dry out excessively.”
Shrinking and swelling
Gijs van Dijk, peat expert at the B-WARE research center in Nijmegen and not involved in this research, is not entirely surprised by the results of his colleagues’ experiment. “You can expect that peat will take a huge hit during long periods of drought. At the same time, there was very little information about what a peat system can really support. We already knew about natural raised bog systems in Siberia, Scandinavia or the Baltic states, for example, that they can shrink and swell under the influence of drought or precipitation. But how long exactly can a drought last before it becomes a problem? These types of experiments can provide a clear answer to that,” says Van Dijk.
Unfortunately, most Dutch raised bogs are no longer part of those ‘resilient natural systems’, Van Dijk notes. “But nature managers now have an extra tool to decide whether they should intervene or not. After how much drought should I start pumping? These types of questions are becoming increasingly relevant in the changing climate.”
Dehydration is a major problem around the Deurnsche Peel, for example, Robroek also agrees. “This is not only because of the change in the climate, but mainly because of the drainage for the many farms around the area. A lot of improvements have been made on the west side of that area through the buyout of several farms, after which 160 hectares of agricultural land have been transformed into nature,” says Robroek. “That area was then considerably wetted. But you wouldn’t even have to buy out companies everywhere. You could also focus on wet forms of agriculture, such as the cultivation of reeds or cattails for building material, or peat moss for potting soil, so that farmers can continue to earn a living there. To protect peat areas, we really need to look at agriculture and the landscape differently.”
In addition, Robroek emphasizes that peat should certainly not be excavated for the potting soil industry, for example. “There is also potting soil on the market that does not contain natural peat,” he advises consumers. “But we still need politics for the really serious steps,” says the researcher. “To ensure that peat continues to absorb carbon instead of emitting it and certainly to ensure that we can keep the peat areas at hand like a thick sponge in times of flooding, these areas really need to be better protected.”
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