Soil Organic Carbon Stock Maps for Belgium: standard deviation (40 m grid)

The Belgian soil organic carbon (SOC) stock map for topsoils (0-30 cm) at the resolution of 40 m x 40 m was composed of 2 regional SOC stock maps. For the regional maps a different approach was used for agricultural land as compared to forest. The maps are based on digital soil mapping approaches using empirical models calibrated to predict the SOC stock and using covariates that are available at a sufficient resolution at the regional scale. All maps are strongly dependent on the Belgian Soil Map (texture and drainage parameters). The regional maps were compiled at a fine resolution (10 m x 10 m grid cells for Flanders and 40 m x 40 m grid cells for Wallonia). Next they were joined (40 m x 40 m grid cells). The regional maps for Flanders were scaled up to the 40 m x 40 m grid of Wallonia. Given the different origin of the individual maps, the uncertainty varies between maps. For instance, a map of the 90 % confidence interval of the SOC stocks was produced for agricultural soils in Wallonia based on a Monte Carlo Approach taking into account both the measurement and the model uncertainty. For Flemish forest soils, spatial and analytical uncertainties were tasks into account using bootstrapping techniques. For Flemish agricultural soils, the uncertainty reported is the model uncertainty on point estimates for each data point, in which the estimated model parameters are simulated 1000 times as being independent normal distributed variables using their model estimation and standard error as distribution parameters. No additional uncertainty is tasks into account for the conversion functions that use the stochastic variables “bulk density”. The metadata are available and allow assessing the uncertainties of the stock estimates in the different component maps. The SOC stock map (resolution of 40 m x 40 m) is the first comprehensive map for Belgium integrating grasslands, croplands and forests. Based on this map another SOC stock map at a resolution of 1 km x 1 km in the coordinate reference system WGS84 was created.