Verification of empirical equations describing subsidence rate of peatland in Central Poland

Currently, due to prolonged soil drought, dehydrated peat soils are particularly exposed to subsidence and, as a consequence, even to disappearance from the natural environment, in which they perform many important functions, e.g. storage of organic carbon and water retention. Therefore, predicting of settlement and disappearance processes of these soils is very important issue. This study was conducted to: (1) determine the degree and rate of subsidence of a drained peatland over 40 years, (2) establish the effect of subsidence on the depth of ditches and a watercourse, (3) verify empirical equations describing the subsidence based on field measurements. The work was carried out on fen in Central Poland which was managed as a grassland until around 2000, and then its use was discontinued. Subsidence rate was estimated from measurements of the peat deposit thickness taken in 11 locations in 1978 and 2018. Fourteen empirical equations used for estimating subsidence rate of drained peatlands were selected to verify the calculations against field data. The average subsidence rate of the studied peatland was relativity low (0.62 cm year−1), which may be associated with abandoning of agricultural use for the last 20 years. Loss of peat thickness varied from 5 to 41% and depended rather on drainage intensity than on its initial depth. In general, six from the verified empirical equations were useful in estimating average subsidence rate. Four equations seemed to be the most useful for deeply drained sites. Estimation of the subsidence solely on the basis of time since drainage may be biased.