Lorenz Curve and Gini Coefficient Reveal Hot Spots and Hot Moments for Nitrous Oxide Emissions

Identifying hot spots and hot moments of nitrous oxide (N₂O) emissions in the landscape is critical for monitoring and mitigating the emission of this potent greenhouse gas. We propose a novel use of the Lorenz curve and Gini coefficient (G) to improve the estimation of the mean as well as the spatial and temporal variation of N₂O emissions from a bioenergy landscape. The analyses indicate that the G was better correlated (R² = 0.72, P < 0.001) with daily N₂O emissions than the coefficient of variation and skewness. A hot moment for N₂O emissions occurred after a storm event, with a heterogeneous spatial distribution of N₂O emissions (G = 0.65); in contrast, CO₂ emissions remained spatially uniform throughout the same period (G = 0.36). Volumetric soil air content below 0.03 m³ m⁻³ occurred more frequently in the wetter footslope positions and created N₂O hot spots, with a high temporal inequality during the growing season (G = 0.75). In contrast, well-drained shoulder positions were cold spots, with uniformly distributed and low N₂O emissions (G = 0.44). The spatial N₂O inequality mirrored the landscape wetness generated by rain events, while biogeochemical equality prevailed in the landscape. The Lorenz curve and G are tools to standardize the spatial and temporal variation of N₂O emissions across diverse landscapes and management scenarios. These two inequality indicators, in association with spatial maps, can help delineate the critical spatial mosaics and temporal windows of N₂O emissions and guide landscape-scale monitoring and mitigation strategies to reduce N₂O emissions.