Comparison of nitrous oxide (N2O) and methane (CH4) fluxes in naturally wet and drained mineral forest soil

The scope of the study is to determine the effect of drainage of mineral soil in forest on nitrous oxide (N2O) and methane (CH4) emissions from soil. We evaluated N2O and CH4 fluxes from soil in pine and birch stands with moderately fertile drained and naturally wet mineral soil. The N2O and CH4 fluxes in naturally wet and drained mineral forest soils are crucial for understanding their respective roles in climate change dynamics and informing sustainable land management practices that can mitigate greenhouse gas emissions. The study was implemented in eighteen stands. We took gas samples periodically (once per month in average) using the opaque chamber method (45 measurement points in total) during 18 months period. Samples were analysed in laboratory using the gas chromatography method. It was assumed that N2O and CH4 fluxes are constant during the whole rotation period, while the average annual fluxes were calculated as sum of average monthly fluxes. We also measured the groundwater (GW) depth, soil and air temperature during the gas sampling and periodically took water samples from perforated water wells for chemical analyses. We found that all measurement sites are net sinks of CH4 removals and sources of N2O emissions. We did not find higher CH4 emissions in wet soil; however, one of the measurement years contained also one of the driest vegetation seasons, and GW level was deeper than usually, potentially resulting in reduction of CH4 emissions. We did not find correlation between the air temperature and N2O or CH4 emissions, as well as between the groundwater level and efflux of these gases. However, higher groundwater level in wet areas is associated with periodic extremes of N2O and CH4 emissions, which cannot be expressed by regression equations. If these extremes are considered, then wet mineral soils are a significant source of N2O emissions, however, they can also be omitted as a non-anthropogenic source.