Quantification of lignite- and vegetation-derived soil carbon using 14C activity measurements in a forested chronosequence

C-14 activity measurements have been used in soil science for studying soil organic matter (SOM) dynamics as well as to separate carbon pools of different age. In this study, we used C-14 activity measurements to quantify the contribution of organic carbon derived from lignite to the total carbon content of soils containing lignite and recently formed organic carbon in mixture. Samples were taken from the forest floor and mineral soils of a chronosequence of rehabilitated mine soils under pine forests (planted in 1966, 1981 and 1987). They were analyzed for their carbon content and C-14 activity. All mineral soils show very old C-14 ages. Old radiocarbon age is generated by contribution of lignite, which does not contain C-14. The lignite content of a sample was calculated by correcting the measured C-14 activity for the C-14 activity level of the recent plant-derived material contributing to SOM. The C-14 activity of the recent carbon component was estimated in each stand by conducting a time series model using the Rothamsted model of soil carbon dynamics. The C-14 activity of recent SOM was rather insensitive (+/- 4% relative) to the tested hypotheses on carbon dynamics in these young forest stands and allowed a precise estimate of the proportion of recent carbon. Lignite accounted for 80% to 93% of total carbon in the mineral topsoil (0-5 cm). The stock of recent soil carbon had a maximum increase between 20 and 32 years, and reached 36 +/- 9 t/ha after 32 years, a value close to the current stock under ancient forests in the area. (C) 2002 Elsevier Science B.V All rights reserved.