Analysis of soil carbon transit times and age distributions using network theories
Journal of Geophysical Research, 114 (G4):
G04025+ (Dec 30, 2009)DOI: 10.1029/2009jg001070
Abstract
The long-term soil carbon dynamics may be approximated by networks of linear compartments, permitting theoretical analysis
of transit time (i.e., the total time spent by a molecule in the system) and age (the time elapsed since the molecule entered
the system) distributions. We compute and compare these distributions for different network configurations, ranging from the
simple individual compartment, to series and parallel linear compartments, feedback systems, and models assuming a continuous
distribution of decay constants. We also derive the transit time and age distributions of some complex, widely used soil carbon
models (the compartmental models CENTURY and Rothamsted, and the continuous-quality Q-Model), and discuss them in the context
of long-term carbon sequestration in soils. We show how complex models including feedback loops and slow compartments have
distributions with heavier tails than simpler models. Power law tails emerge when using continuous-quality models, indicating
long retention times for an important fraction of soil carbon. The responsiveness of the soil system to changes in decay constants
due to altered climatic conditions or plant species composition is found to be stronger when all compartments respond equally
to the environmental change, and when the slower compartments are more sensitive than the faster ones or lose more carbon
through microbial respiration.