Greenhouse gas emissions from alluvial soils in grassland and cropland in northern part of Europe's temperate climate zone (Latvia)

Alluvial soils have high importance for both agriculture and biodiversity; however, these soils can also contribute to greenhouse gas (GHG) emissions including carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). In this study, we examined GHG fluxes of three grassland and two cropland sites with alluvial soils in Abava river floodplain, Latvia (Europe). Soil CO2 fluxes representing heterotrophic respiration (Rhet) were determined using a portable CO2 gas analyser, while ecosystem respiration (Reco), soil CH4 and N2O fluxes were quantified using a manual closed chamber method combined with gas chromatography. Most alluvial soils acted as source of GHG emissions with the exception of two grassland site where annual CH4 exchange reflected a slight CH4 removal from the atmosphere. Mean total GHG emissions (sum of net CO2, CH4 and N2O) were 7.0 ± 3.3 t CO2 eq./ha/year in grassland sites and 14.5 ± 4.8 t CO2 eq./ha/year in cropland sites. Net CO2 contributed the most to total annual GHG emissions with mean values of 6.2 ± 3.3 t CO2/ha/year in grassland and 13.6 ± 4.8 t CO2/ha/year in cropland sites. Although the number of study sites is limited, the results support that, in the context of climate change mitigation, grassland represents a more climate-friendly type of floodplain land use than cropland in the hemiboreal region.