The use of radiocarbon to constrain current and future soil organic matter turnover and transport in a temperate forest

• Published in: Journal of geophysical research. Biogeosciences Vol. 119; no. 3; pp. 372 - 391
• Main Authors: Braakhekke, Maarten C., Beer, Christian, Schrumpf, Marion, Ekici, Altug, Ahrens, Bernhard, Hoosbeek, Marcel R., Kruijt, Bart, Kabat, Pavel, Reichstein, Markus
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-03-2014
• Subjects: age calibration; Bayesian analysis; Bayesian calibration; c-14 data; Calibration; Carbon; climate-change; co2; Deciduous forests; Decomposition; eddy covariance; global vegetation models; Mathematical models; Organic carbon; Organic matter; Pools; radiocarbon; Raw materials; Reduction; residence times; Respiration; Soil (material); soil organic carbon; Soil organic matter; Soils; SOM transport; storage; Subsoils; Temperate forests; terrestrial carbon-cycle; Tillage; Topsoil; Transport; vertical profile; vertical-distribution
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2013JG002420

We investigated the merits of radiocarbon measurements for estimating soil organic matter (SOM) turnover and vertical transport for a temperate deciduous forest in Germany. Eleven parameters, defining decomposition and transport in the soil carbon model SOMPROF, were estimated using a Bayesian approach based on organic carbon measurements and radiocarbon concentration of SOM and heterotrophic respiration. The addition of radiocarbon data had strong effects on the parameters, most importantly a reduction of the decomposition and production rate of the slowest SOM pool by an order of magnitude, and a similar reduction in advective SOM transport. The modified parameters further led to changes in the partitioning of SOM over the different model pools. The calibration results were subsequently used to perform transient soil carbon projections for the period 1901–2100. These simulations were run with parameter sets from calibrations both with and without radiocarbon. The results show an increase over time of topsoil carbon and a decrease in the subsoil, adding to a net gain overall. Near the end of the 21st century, total carbon stocks stabilize and—for the radiocarbon‐constrained model—start to decrease. However, the changes are small compared to the total stocks. The model results for the calibrations with and without radiocarbon are in general quite similar, but the latter shows notably higher heterotrophic respiration fluxes. Constraining the model with radiocarbon yielded only a small reduction of uncertainty for the total carbon stocks, while for the individual depth compartments, the uncertainty was increased.
Key Points
SOM turnover and transport was estimated using Bayesian calibration
Radiocarbon data strongly improved constraint of turnover rate of slow pool
Predictive simulation showed small increase of soil C stocks in 21st century