The Arctic tundra is renowned for being one of, if not the most, harshest environments on Earth. It is constantly covered in permafrost that freezes the ground metres deep, with the exception of the short summer months when flowers bloom.
The threat of carbon dioxide escaping from the tundra as it thaws is widely known and recognised. However, a new study, led by Carolina Voigt of the University of Eastern Finland, believes that the threat of nitrous oxide has been severely underestimated.
‘Often overlooked is the fact that permafrost soils are also large nitrogen reservoirs,’ she says, ‘with a conservative estimate of 67 billion tons of total nitrogen in the upper three metres.’ Voigt goes on to put the magnitude of the nitrogen stocks into perspective: ‘The permafrost stocks are more than 500 times larger than the annual nitrogen load added as fertiliser to soils globally.’
Voigt collected 16 samples of permafrost peatland from different locations in Finnish Lapland to assess whether permafrost thaw will increase N2O emissions into the atmosphere. In order to account for different scenarios, the researchers kept the samples in two separate post-thaw conditions: one ‘dry’ scenario (an unaltered water table) and one ‘wet’ scenario (a raised water table).
The results highlighted those areas of tundra with vegetation emit very little nitrous oxide and actually help with reducing emissions. It was found that areas without vegetation, and that were more exposed, released small yet significant levels of the minor greenhouse gas.
The results mirror a previous study done in Northern Russia by Maija Repo at the UEF’s Kuopio campus. Repo and her team found that during the snow-free season, the peatland emitted as much N2O as a tropical forest does in a year.
What is worrying about the results from Voigt and Repo’s studies is that the Arctic is browning, even despite recent trends until 2011 showing that the Arctic has experienced overall increases in the amounts of greenery.
This means that there is less vegetation overall and that the tundra is more vulnerable to leaking nitrous oxide as the permafrost thaws. This could be attributed to the fact that the lack of plants decreases the competition for mineral nitrogen, therefore allowing nitrate to build up in the soil, which bacteria metabolise to produce nitrous oxide.
Although nitrous oxide is classed as a minor greenhouse gas, it is roughly 300 times more powerful than carbon dioxide. Back in 2009, Repo emphasised these fears to New Scientist magazine, saying: ‘Since the flow of the gas from the peat circles is so high, even a small increase in bare surfaces would cause significant changes in N2O emissions.’
The study makes it clear that, while these emissions are dangerous, the scale of the impact is highly dependent on external factors. As Voigt says: ‘Our results suggest that the magnitude of future N2O emissions depends mainly on landscape changes that alter soil moisture conditions.’