1 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University2 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University3 unknown4 The University of Sydney5 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University6 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University
Estimation of carbon contents and stocks are important for carbon sequestration, greenhouse gas emissions and national carbon balance inventories. For Denmark, we modeled the vertical distribution of soil organic carbon (SOC) and bulk density, and mapped its spatial distribution at five standard soil depth intervals (025, 5215, 15230, 30260 and 602 100 cm) using 18 environmental variables as predictors. SOC distribution was influenced by precipitation, land use, soil type, wetland, elevation, wetness index, and multi-resolution index of valley bottom flatness. The highest average SOC content of 20 g kg21 was reported for 025 cm soil, whereas there was on average 2.2 g SOC kg21 at 602100 cm depth. For SOC and bulk density prediction precision decreased with soil depth, and a standard error of 2.8 g kg21 was found at 602100 cm soil depth. Average SOC stock for 0230 cm was 72 t ha21 and in the top 1 m there was 120 t SOC ha21. In total, the soils stored approximately 570 Tg C within the top 1 m. The soils under agriculture had the highest amount of carbon (444 Tg) followed by forest and semi-natural vegetation that contributed 11% of the total SOC stock. More than 60% of the total SOC stock was present in Podzols and Luvisols. Compared to previous estimates, our approach is more reliable as we adopted a robust quantification technique and mapped the spatial distribution of SOC stock and prediction uncertainty. The estimation was validated using common statistical indices and the data and high-resolution maps could be used for future soil carbon assessment and inventories.