Modeling the vertical soil organic matter profile using Bayesian parameter estimation

[摘要] The vertical distribution of soil organic matter (SOM) in the profile mayconstitute an important factor for soil carbon cycling. However, theformation of the SOM profile is currently poorly understood due toequifinality, caused by the entanglement of several processes: input fromroots, mixing due to bioturbation, and organic matter leaching. In this studywe quantified the contribution of these three processes using Bayesianparameter estimation for the mechanistic SOM profile model SOMPROF. Based onorganic carbon measurements, 13 parameters related to decomposition andtransport of organic matter were estimated for two temperate forest soils: anArenosol with a mor humus form (Loobos, the Netherlands), and a Cambisol withmull-type humus (Hainich, Germany). Furthermore, the use of the radioisotope²¹⁰Pb_ex as tracer for vertical SOM transport was studied.For Loobos, the calibration results demonstrate the importance of organicmatter transport with the liquid phase for shaping the vertical SOM profile,while the effects of bioturbation are generally negligible. These results arein good agreement with expectations given in situ conditions. For Hainich, thecalibration offered three distinct explanations for the observations (threemodes in the posterior distribution). With the addition of²¹⁰Pb_ex data and prior knowledge, as well as additionalinformation about in situ conditions, we were able to identify the mostlikely explanation, which indicated that root litter input is a dominantprocess for the SOM profile. For both sites the organic matter appears tocomprise mainly adsorbed but potentially leachable material, pointing to theimportance of organo-mineral interactions. Furthermore, organic matter in themineral soil appears to be mainly derived from root litter, supportingprevious studies that highlighted the importance of root input for soilcarbon sequestration. The ²¹⁰Pb_ex measurements added onlyslight additional constraint on the estimated parameters. However, withsufficient replicate measurements and possibly in combination with othertracers, this isotope may still hold value as tracer for SOM transport.

[学科分类] 地球化学与岩石