Nitrous oxide and methane exchange in two small temperate forest catchments—effects of hydrological gradients and implications for global warming potentials of forest soils
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The magnitude of greenhouse gas (GHG) flux rates may be important in wet and intermediate wet forest soils, but published estimates are scarce. We studied the surface exchange of methane (CH4) and nitrous oxide (N2O) from soil along toposequences in two temperate deciduous forest catchments: Strødam and Vestskoven. The soil water regime ranged from fully saturated to aerated within the catchments. At Strødam the largest mean flux rates of N2O (15 μg N2O-N m−2 h−1) were measured at volumetric soil water contents (SWC) between 40 and 60% and associated with low soil pH compared to smaller mean flux rates of 0-5 μg N2O-N m−2 h−1 for drier (SWC < 40%) and wet conditions (SWC > 80%). At Vestskoven the same response of N2O to soil water content was observed. Average CH4 flux rates were highly variable along the toposequences (−17 to 536 μg CH4-C m−2 h−1) but emissions were only observed above soil water content of 45%. Scaled flux rates of both GHGs to catchment level resulted in emission of 322 and 211 kg CO2-equivalents ha−1 year−1 for Strødam and Vestskoven, respectively, with N2O contributing the most at both sites. Although the wet and intermediate wet forest soils occupied less than half the catchment area at both sites, the global warming potential (GWP) derived from N2O and CH4 was more than doubled when accounting for these wet areas in the catchments. The results stress the importance of wet soils in assessments of forest soil global warming potentials, as even small proportions of wet soils contributes substantially to the emissions of N2O and CH4.
KeywordsDrainage Forest soil Methane Nitrous oxide Scaling Wet soils
We are grateful to Preben Frederiksen, Xhevat Haliti, Mads Krag and Yunting Fang for help in the field. This study was part of NitroEurope IP. The research was further supported financially by the RECETO PhD school and the Faculty of Life Sciences both at University of Copenhagen.
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