Methane emissions from Arctic ponds are sensitive to warming-induced vegetation changes

The Arctic is warming four times faster than the globe and this warming causes many changes in the northern landscapes including rising emissions of greenhouse gases. Previous studies investigating future Arctic greenhouse-gas emissions focused on the tundra soils, however Arctic landscapes are abounded with waterbodies, and many of these waterbodies are small and shallow. This makes them especially sensitive to warming and there is limited knowledge on how methane emissions from Arctic ponds will change under warming.

To address this knowledge gap, a new study of international team of scientists led by researchers from the Max Planck Institute for Meteorology and Universität Hamburg utilizes a novel model.  With this model they study the response of methane emissions from ponds to warming for a study site in Eastern Siberia. The study reveals that the ponds are very sensitive to warming and the simulated emissions increase strongly with warming for several reasons.

The higher temperatures themselves directly cause some of the emission increase. Surprisingly, most of the emission increase is mediated through vegetation changes: As temperatures increase, so does the productivity of the vegetation in and around the pond. These vegetation changes facilitate methane emissions in two ways. First, sedges which grow inside the ponds have hollow stems through which methane produced in the sediment can bypass the water column and directly escape to the atmosphere. This plant-mediated transport is the most efficient emission pathway for methane. With a higher plant density, more methane can be emitted this way. Second, most of the methane produced in the ponds is derived from organic material provided by the vegetation. Thus, with more vegetation methane production in the pond surges.

Zoé Rehder, first author of the paper and a member of the Cluster of Excellence CLICCS: “Our goal is to estimate pond methane emissions on pan-Arctic scale. We argue that plant-mediated transport and the cover fraction of sedges in waterbodies need to be mapped more thoroughly than at present.”