Number of Chamber Measurement Locations for Accurate Quantification of Landscape‐Scale Greenhouse Gas Fluxes: Importance of Land Use, Seasonality, and Greenhouse Gas Type

Accurate quantification of landscape soil greenhouse gas (GHG) exchange from chamber measurements is challenging due to the high spatial‐temporal variability of fluxes, which results in large uncertainties in upscaled regional and global flux estimates. We quantified landscape‐scale (6 km2 in central Germany) soil/ecosystem respiration (SR/ER‐CO2), methane (CH4), and nitrous oxide (N2O) fluxes at stratified sites with contrasting landscape characteristics using the fast‐box chamber technique. We assessed the influence of land use (forest, arable, and grassland), seasonality (spring, summer, and autumn), soil types, and slope on the fluxes. We also evaluated the number of chamber measurement locations required to estimate landscape fluxes within globally significant uncertainty thresholds. The GHG fluxes were strongly influenced by seasonality and land use rather than soil type and slope. The number of chamber measurement locations required for robust landscape‐scale flux estimates depended on the magnitude of fluxes, which varied with season, land use, and GHG type. Significant N2O‐N flux uncertainties greater than the global mean flux (0.67 kg ha−1 yr−1) occurred if landscape measurements were done at <4 and <22 chamber locations (per km2) in forest and arable ecosystems, respectively, in summer. For CO2 and CH4 fluxes, uncertainties greater than the global median CO2‐C flux (7,500 kg ha−1 yr−1) and the global mean forest CH4‐C uptake rate (2.81 kg ha−1 yr−1) occurred at <2 forest and <6 arable chamber locations. This finding suggests that more chamber measurement locations are required to assess landscape‐scale N2O fluxes than CO2 and CH4, based on these GHG‐specific uncertainty thresholds.Plain Language Summary: Greenhouse gas emissions are subject to high spatial and temporal variability, leading to large uncertainties in regional and global estimates. We quantified fluxes of soil and ecosystem respiration (SR/ER‐CO2), methane (CH4) and nitrous oxide (N2O) at the landscape scale (6 km2 in central Germany). We determine the number of measurement chambers required to estimate landscape fluxes within globally significant uncertainty thresholds. Our results show a stronger influence of season and land use, as opposed to soil type and topography. The number of chambers required for robust landscape‐wide flux estimates depended on the size of the fluxes, which varied by season, land use and GHG type. An increase in the number of monitoring sites significantly reduced the uncertainties estimation on the whole landscape. Significant uncertainties in N2O fluxes above the global annual mean was found when landscape measurements were made at <4 monitoring sites in forests and <22 monitoring sites (per km2) in cropland ecosystems during the summer period. For SR/ER‐CO2 fluxes, as few as <2 was sufficient in forest ecosystems and under <6 in cropland ecosystems. This result implies that in general more monitoring sites are needed to assess landscape‐scale N2O fluxes than for CO2 and CH4 fluxes.Key Points: Land use and seasonality rather than soil type and slope strongly influenced soil greenhouse gas (GHG) fluxes at a landscape‐scale. The minimum number of chamber locations required for robust landscape‐scale flux estimates depends on the season, land use, and GHG type. Chamber locations required to reduce uncertainties of landscape flux estimates declined as follows N2O > CO2 > CH4.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659https://doi.org/10.5281/zenodo.682111