Black (pyrogenic) carbon in soils and waters: a fragile data basis extensively interpreted

Black (pyrogenic) carbon (BC) has its origin in incomplete combustion of organic matter. It is considered to be a stable fraction of soil organic carbon (SOC) accounting for a great proportion of SOC in many soils. The aim of this article is to verify the reliability of the three most widely applied methods to determine BC in soils: the benzene polycarboxylic acid (BPCA) method, the UV/NMR method and the (CNMR)-C-13 method. All these methods strongly overestimate BC in soil and dissolved BC in waters. The main reason for the overestimation can be attributed to the fact that these three methods measure the polycyclic aromatic carbon (PAC) present in BC. However, PAC structures are also a component of humic substances so that a part of humic C is measured as BC. It can be concluded that the importance of BC in soil and waters is strongly overestimated and should be critically reevaluated.