Shrinkage of organic soils

Due to their genesis from dead and - more or less - preserved organic material (e.g. peat moss, sedge, wood, detritus) peat and other organic soils are characterised by a high carbon content and unique physical properties, e.g. low bulk density, very high porosity and compressibility. The water content plays a major role here. When an organic soil is desiccated, it shrinks due to the reduction of the pore volume. Although there are shrinking mineral (clay containing) soils,  the shrinkage properties of those two soil groups differ greatly.

Since shrinkage and swelling lead to changes in surface elevation, governed by groundwater level and soil moisture, a review study and meta-analysis - amended by own measurements - was carried out as part of "Peatland monitoring program for climate protection - open land" in order to identify the most important soil-specific influencing factors. Besides its relevance for determining greenhouse gas emissions (based on the long-term subsidence), shrinkage is important for the determination of volume-based soil parameters (e.g. bulk density, water content, available water capacity) as the reference volume can change during the measurements. This can significantly influence the quality of the determined parameters.

We found a wide range and large scattering of shrinkage values depending on the botanical composition and degree of decomposition of the substrate. The carbon content and the bulk density were only very weak predictors for shrinkage.
 
https://doi.org/10.1002/vzj2.20264