On 13 October at 11:15 Birgit Viru will defend her doctoral thesis “Snow cover dynamics and its impact on greenhouse gas fluxes in drained peatlands in Estonia” for obtaining the degree of Doctor of Philosophy (in Physical Geography).
Professor Jaak Jaagus, UT Institute of Ecology and Earth Sciences
Professor Ülo Mander, UT Institute of Ecology and Earth Sciences
Associate Professor Annalea Lohila, Finnish Meteorological Institute (Finland)
Since the beginning of Industrial Revolution Earth´s average temperature has risen by about one degree centigrade. The change in average winter temperatures in northern Europe has been greater than the global average. Air temperature is the main factor which determines the duration and depth of snow cover. Snow cover, in turn, affects winter greenhouse gas (GHG) emissions. The aim of this dissertation was to analyze the dynamics of snow cover in Estonia and its effect GHG emissions in winter.
Territorial differences in snow cover parameters in Estonia are considerable. Snow cover duration varied between 61 days in Western-Estonia and 130 days on uplands of south-eastern Estonia. As an Estonian average, the snow cover period has been shortened by 27 days in 66 years, mainly due to the earlier spring melting.
GHG were measured from two abandoned peat extraction areas and two drained peatland forests. Both ecosystems are important GHG sources.
The values of carbon dioxide (CO2) emissions were similar between abandoned peat extraction areas and drained peatlands, the emission was positively correlated with soil and air temperatures. Wintertime CO2 efflux made up 10–25% of the annual release.
Drained forests were methane (CH4) sinks and abandoned peat extraction areas emitters (sources). Higher CH4 emission values were measured at high groundwater depths (<20 cm). Wintertime CH4 fluxes made up 31–52% of annual release at the abandoned peat extraction areas and 33–49% of annual consumption in the drained forests.
Nitrous dioxide (N2O) fluxes from drained forests were significantly higher than those from the abandoned peat extraction areas. Wintertime N2O release from the drained forests accounted for 87% of the total annual emission. Emissions during freezing/thawing events were particularly high.
Our hypothesis on the snow cover effect was only partly supported, showing both a positive and negative impact on different sites and gases. In general, thin and scattered snow cover during the freeze-thaw periods initiates GHG emissions. Regarding trends in snow cover duration and thickness, more wintertime emissions of GHGs are expected in future.