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

Abstract

<p>Accurate quantification of landscape soil greenhouse gas (GHG) exchange from chamber<br />measurements is challenging due to the high spatial-temporal variability of fluxes, which results in large<br />uncertainties in upscaled regional and global flux estimates. We quantified landscape-scale (6 km<sup>2</sup> in central<br />Germany) soil/ecosystem respiration (SR/ER-CO<sub>2</sub>), methane (CH<sub>4</sub>), and nitrous oxide (N<sub>2</sub>O) fluxes at<br />stratified sites with contrasting landscape characteristics using the fast-box chamber technique. We assessed<br />the influence of land use (forest, arable, and grassland), seasonality (spring, summer, and autumn), soil<br />types, and slope on the fluxes. We also evaluated the number of chamber measurement locations required to<br />estimate landscape fluxes within globally significant uncertainty thresholds. The GHG fluxes were strongly<br />influenced by seasonality and land use rather than soil type and slope. The number of chamber measurement<br />locations required for robust landscape-scale flux estimates depended on the magnitude of fluxes, which varied<br />with season, land use, and GHG type. Significant N<sub>2</sub>O-N flux uncertainties greater than the global mean<br />flux (0.67 kg ha<sup>−1</sup> yr<sup>−1</sup>) occurred if landscape measurements were done at <4 and <22 chamber locations<br />(per km<sup>2</sup>) in forest and arable ecosystems, respectively, in summer. For CO<sub>2</sub> and CH<sub>4</sub> fluxes, uncertainties<br />greater than the global median CO<sub>2</sub>-C flux (7,500 kg ha<sup>−1</sup> yr<sup>−1</sup>) and the global mean forest CH<sub>4</sub>-C uptake rate<br />(2.81 kg ha<sup>−1</sup> yr<sup>−1</sup>) occurred at <2 forest and <6 arable chamber locations. This finding suggests that more<br />chamber measurement locations are required to assess landscape-scale N<sub>2</sub>O fluxes than CO<sub>2</sub> and CH<sub>4</sub>, based on<br />these GHG-specific uncertainty thresholds.</p>