Towards climate-smart sustainable management of agricultural soils: Indicators for successful carbon sequestration and greenhouse gas mitigation by rewetting cultivated peat soils (INSURE) Deliverable 6

Three locations in Europe (wet river valley (Denmark), coastal peatland (The Netherlands) and broad river floodplain (Switzerland)) were selected for which two to three years of measurements of hydrological variables and CO2 exchange fluxes were available for some period between 2015 and 2023. The hydrology, grass growth and CO2 fluxes of these sites were modelled with the SWAP-ANIMO model using the available measurement period for model input and calibration. Model simulations were used to improve the understanding of the hydrological drivers of each site and to
obtain estimates of the different pools contributing to the measured CO2 fluxes using a period of 10 years (2014-2023). Rewetting was considered either by calibration on direct measurements of an actual rewetting measure (Denmark, The Netherlands) or extrapolation of the reference simulation (Switzerland). Also, the potential impact of climate change on the rate of peat oxidation was modelled for these sites for both the reference and rewetting measure. The relation between the yearly averaged groundwater level and the CO2 emission related to peat oxidation was remarkably similar for the three sites. In all cases, deeper yearly-averaged groundwater levels resulted in higher peat oxidation and CO2 emissions. The relation was, however,
affected by the type of rewetting measure, which was partly related to the existence of a correlation between yearly averaged soil temperatures and yearly averaged groundwater levels (i.e. a higher soil temperature tends to coincide with deeper groundwater levels) and partly related to the nature of the rewetting measure (limiting only drainage, or also promoting infiltration). Also, the steepness of
the relation between groundwater levels and peat oxidation was found to increase with increasing temperatures for each of the sites due to the relation between temperature and peat oxidation rates.