Soil organic carbon evolution at the regional scale : overcoming uncertainties & quantifying driving forces
(2009)
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- Authors
- Supervisors
- van Wesemael, Bas
- Abstract
- (en) "Soil is a non-renewable resource (…) vital to human activities and ecosystem survival" (EC, 2006). Soil protection requires studies and monitoring based on indicators of its quality. Soil organic matter content (SOM) is one the most relevant of these indicators. However, the inventory of soil organic carbon (SOC), the main component of SOM, is challenging at the regional scale due to its inherent large spatial variability and its slow dynamics. Uncertainties can reach high levels preventing both the detection of significant SOC changes through time and the identification of the driving forces involved. This, in turn, undermines the ability to implement judicious policies for SOC conservation or sequestration. Given such a context, this thesis aims to improve the understanding of long-term SOC dynamics in agricultural soils at the regional scale. The specific objectives are: (i) to detect the SOC stock changes under agriculture in southern Belgium between 1955 and 2005, (ii) to quantify the uncertainties and validate the methodology used, and (iii) to discriminate the driving forces involved in the observed SOC evolution. This thesis shows that significant changes in SOC stocks can be detected thanks to the stratification of the study area into spatial homogeneous units (based on land use, soil type, climate and agricultural region) and to the re-sampling of soil profiles from the 1950s. Despite uncertainties on the SOC stock assessment mainly arising from the laboratory analyses and the spatial variability, an opposite behaviour in the change in SOC stock is found between units under cropland (–12% on average in the plough layer) and units under grassland (+20% in the 0-30cm layer). The main driving forces of SOC evolution are the agricultural management for cropland and the soil texture (clay content) for grassland. The impact of climate change (i.e. of the changes in the mean annual temperature and precipitation) is of minor importance. Results also shows that the “baseline effect” (i.e. the inversely proportional effect of the initial SOC content on the SOC evolution) is responsible for an important part of the SOC variability. This challenges the assumption used in most SOC dynamic models that the initial SOC content represents steady state conditions. Based on these results, mixed linear models were built to predict the SOC stock in 1955, 2005 and its change between those two periods. However, these models still present large uncertainties after validation. At the end of the thesis, the perspective of using the re-sampled soil profiles as part of a future SOC monitoring network in southern Belgium – CARBOSOL – is investigated.
- Affiliations
Citations
Goidts, E. (2009). Soil organic carbon evolution at the regional scale : overcoming uncertainties & quantifying driving forces. https://hdl.handle.net/2078.5/130323