Greenhouse gas emissions from beaver ponds exceed emissions from shallow lakes in subantarctic ecosystems

Inland waters are generally perceived as net-sources of greenhouse gases (GHG) to the atmosphere, provided they receive large amounts of terrestrial organic matter, which enhances the production of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Nonetheless, the role of subantarctic brown-water shallow lakes (SLs) and beaver ponds (BPs) in the carbon cycle remains largely unknown. In this study, diffusive GHG emissions of CH₄, CO₂, and N₂O from the air-water interface were measured during two consecutive ice-free periods in four SLs and four BPs from southern Patagonia (Tierra del Fuego, Argentina). Additionally, the CH₄ ebullitive fluxes were measured in two SLs and two BPs during the second sampling season. Results indicate that both water body types are net GHG emission sources; BPs emissions doubled those by brown SLs, both in CO₂ (BPs, 55 ± 22 vs SLs, 26 ± 13 mmol m^-2 d^-1) and CH₄ emissions (BPs, 3.8 ± 3.0 vs SLs, 1.1 ± 0.8 mmol m^-2 d^-1). N₂O emissions were low in both SLs and BPs (15.2 ± 26 and 11 ± 35 μmol m^-2 d^-1, respectively). Furthermore, CH₄ ebullitive fluxes were higher in BPs than SLs (0.9 ± 1.0 and 0.3 ± 0.4 mmol m^-2 d^-1, respectively). Our findings provide quantitative data on GHG fluxes between water and the atmosphere in subantarctic lakes and ponds. These results may have significant implications for management practices, since beavers were introduced to the region a few decades ago and BP are currently releasing large volumes of GHG to the atmosphere, yet in smaller amounts than their counterparts in the northern hemisphere, where beavers are native.