Mapping of distribution of Soil Organic Carbon and CO2 emissions in the Ferrara province: comparison of C contents in 1937 and 2022

Global warming is accelerating soil organic matter (SOM) degradation and increasing the release of greenhouse gases (GHGs; e.g., CO2, CH4, N2O) into the atmosphere. In addition, unsustainable agricultural practices, agricultural land use and land cover change (LULCC) exacerbate the process and account for 20% of the total CO2 emissions. In particular, over the last century LULCC have reduced SOM and released CO2 in Northern Italy. Today the Ferrara province, located in the easternmost part of the Po River plain in Northern Italy, has soils with a large range of SOM content that include peatlands with very high SOM, which is the result of a wetland reclamation program of palustrine environment that started before the World War II and ended in the 1970s, increasing the agricultural production area by ~78000 ha. In 1937 Ferrari et al. (1937) conducted a survey of the soil of the entire Ferrara province to assess the physicochemical properties of the soils and the SOM content in the 0-30 cm topsoil layer. In this research we compared the SOM content data collected by Ferrari et al. (1937) with new topsoil geochemical data collected from the same sample locations in 2022. In particular, for each location the total (TC) and organic (OC) carbon contents and the relative isotopic signatures (δ13CTC; δ13COC) of the samples obtained in 2022 were measured trough an elemental isotope analyzer coupled with an isotopic ratio mass spectrometer (EA-IRMS). The distributions of C fractions of the samples collected in 1937 and 2022 were represented into maps and used to calculate the carbon dioxide equivalent (CO2 eq) released in the atmosphere in 85 years. Comparison of SOC maps form 1937 and 2022 indicates that most of the Ferrara area suffered a significant SOC loss (ΔOC85 years from 0.05 to 18.57 wt%), with the exception of northern areas in which the peat nature of the soil has been preserved with SOC up to 25 wt%. However, it is important to note that the highest decrease occurred just in reclaimed peatlands coupled with a strong CO2 emission due to the conversion of the peatland into croplands and the unsustainable farming activities encouraged by the fertility of these soils. Finally, we also measured the 13C/12C on the 2022 soil samples and generated a present-day map of the SOC isotopic ratios. The isotopic signature was used as a tool to evaluate changes in soil carbon stocks that had occurred over long time periods, and in the future it will be used as a benchmark to measure C changes. Works like this highlight the importance to create and to update OC content inventories in order to estimate the SOC stock loss after several years and to calculate the amount of CO2 eq released in the atmosphere.