The bulk UMI-77 δ13C value (Fig. 5) in the NDE was around − 27‰ in the topsoil increasing to − 25.5‰ at 40–60 cm depth indicating input of C3 plant material (O' Leary, 1988) to the topsoil, which was increasingly mineralized down to 60 cm soil depth. However, a strong shift towards more negative δ13C value of − 32.1‰ in 70–80 cm depth was observed, likely be due to input of lacustrine algae or photosynthetic bacteria (Glaser and Zech, 2005). In the reference soil, δ13C fluctuated around − 25‰ throughout the soil profile with slightly lower δ13C value of − 28.4‰ in 30–40 cm depth. Several factors (e.g. the photosynthetic pathway of vegetation (C3/C4 metabolic pathway), SOM degradation or water) influence the natural abundance of 13C in bulk soil organic matter (Zech et al., 2007).
3.1.3. Stable SOM (black carbon)
3.1.4. Multi-element signature
Total element concentrations are shown in Table 2. Compared to the reference soil, nutrients show levels of enhancements of up to 13× for Mg, 25 × for Na, 15 × for K and 554 × for Ca. Heavy metals such as Ba, Cu, Fe, Zn and Mn are up to 24 ×, 38 ×, 6 ×, 8 × and 20 × times enriched in the NDE, respectively.