Measurements versus Estimates of Soil Subsidence and Mineralization Rates at Peatland over 50 Years (1966–2016)

The size of peat subsidence at Solec peatland (Poland) over 50 years was determined. The field values for subsidence and mineralization were compared with estimates using 20 equations. The subsidence values derived from equations and field measurements were compared to rank the equations. The equations that include a temporal factor (time) were used to forecast subsidence (for the 20, 30 and 40 years after 2016) assuming stable climate conditions and water regime. The annual rate of subsidence ranged from 0.08 to 2.2 cm year−1 (average 1.02 cm year −1). Equation proposed by Jurczuk produced the closest-matching figure (1.03 cm year−1). Applying the same equation to calculate future trends indicates that the rate of soil subsidence will slow down by about 20% to 0.82 cm year−1 in 2056. With the measured peat subsidence rate, the groundwater level (57–72 cm) was estimated and fed into equations to determine the contribution of chemical processes to the total size of subsidence. The applied equations produced identical results, attributing 46% of peat subsidence to chemical (organic matter mineralization) processes and 54%—to physical processes (shrinkage, organic matter consolidation). The belowground changes in soil in relation to groundwater level have been neglected lately, with GHGs emissions being the main focus.