Estimating soil organic carbon stock change at multiple scales using machine learning and multivariate geostatistics

• Published in: Geoderma Vol. 403; p. 115356
• Main Authors: Szatmári, Gábor, Pásztor, László, Heuvelink, Gerard B.M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-12-2021
• Subjects: Change of support; Geostatistical simulation; Random forest; Soil organic carbon; Spatio-temporal assessment; Uncertainty assessment; Geostatistical simulation; Change of support; Uncertainty assessment; Random forest; Spatio-temporal assessment; Soil organic carbon
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2021.115356

•Use of geostatistics is indispensable when spatial aggregation with quantified uncertainty is targeted.•Spatial aggregation decreases uncertainty and supports detection of statistically significant SOC stock change.•Many counties in Hungary had a statistically significant topsoil SOC stock increase between 1992 and 2010.•The total topsoil SOC stock increase in Hungary between 1992 and 2010 was predicted as 14.79Tg C.
Many national and international initiatives rely on spatially explicit information on soil organic carbon (SOC) stock change at multiple scales to support policies aiming at land degradation neutrality and climate change mitigation. In this study, we used regression cokriging with random forest and spatial stochastic cosimulation to predict the SOC stock change between two years (i.e. 1992 and 2010) in Hungary at multiple aggregation levels (i.e. point support, 1 × 1 km, 10 × 10 km square blocks, Hungarian counties and entire Hungary). We also quantified the uncertainty associated with these predictions in order to identify and delimit areas with statistically significant SOC stock change. Our study highlighted that prediction of spatial totals and averages with quantified uncertainty requires a geostatistical approach and cannot be solved by machine learning alone, because it does not account for spatial correlation in prediction errors. The total topsoil SOC stock for Hungary was predicted to increase between 1992 and 2010 with 14.9Tg, with lower and upper limits of a 90% prediction interval equal to 11.2Tg and 18.2Tg, respectively. Results also showed that both the predictions and uncertainties of the average SOC stock change were smaller for larger spatial supports, while spatial aggregation also made it easier to obtain statistically significant SOC stock changes. The latter is important for carbon accounting studies that need to prove in Measurement, Reporting and Verification protocols that observed SOC stock changes are not only practically but also statistically significant.