Search

Archaeological anthrosols constitute a heritage of long-term carbon storage and soil fertility. Their anthropogenic features are affected by the type and intensity of ancient human activities. Human activities can follow a gradation of disturbance intensity, with lower intensity related to a weak human pollution of natural soil, and stronger intensity related to anthropogenic materials inputs (e.g. refuse pits). Soil properties are indeed deeply modified by the addition of objects (e.g. bones, ceramic) and of organic matter with distinct chemical composition and biological stability (e.g. charcoal). The aim of the study was to establish a new analytical approach to distinguish intensities of human activities, based on organic matter characteristics. To this end, we studied intertropical soil profiles (0-120 cm) from Cameroon, Brazil and Bolivia, with spatial or temporal intensity variations of human activities. We used standard compositional parameters (hydrogen index, HI, and oxygen index, OI) and advanced thermal parameters (I-index and R-index) from Rock-Eval® pyrolysis, as well as magnetic susceptibility, to characterize anthrosols.Results demonstrated the potential of Rock-Eval® pyrolysis parameters to identify human activities changes. First, the deviation of I-index (delta-I) between our samples and a reference value from natural sites informed about the intensity of human impacts, allowing for the distinction between artificial infilling of refuse pits and soil profiles with no or few human impacts. Second, positive HI:OI correlation established the importance of charcoal as main organic C source. The magnetic susceptibility informed about the presence of burnt soils in a Brazilian and one of the Bolivian sites. The combination of all these parameters, when represented with soil depth, allowed for the estimation of temporal changes in Brazilian and Bolivian sites. The topsoils were similar for all sites, relative to a low intensity of human activities or to the resumption of natural pedogenesis, thereby alleviating the effects of ancient human activities on organic matter characteristics. In contrast, the subsoils exhibited higher intensities of ancient human activities, with even higher values of intensities in Bolivian sites, thereby evidencing the long-term conservation of their effects on organic matter characteristics.To conclude, anthropogenic activities may durably affect organic matter characteristics in tropical sites, even after several centuries. Beyond being of interest for archaeological research, this new approach raises questions about the long-term consequences of our current human activities.

In the mitigating strategies of human impact on environments, the biochar addition to shallow soil horizon represents a promising way among the existing Carbon Dioxide Removal technique. This study is part of a project that aims at evaluating the impact of the presence of biochar in soils on the growth of roots. Geophysical techniques are a good candidate for non-invasive investigation and field monitoring. Among the existing techniques, Electrical Resistivity Tomography (ERT) has already shown great potential for detecting the presence and growth of roots in agricultural soils.In this study, our goal is to test whether ERT is able to track changes in root growth in a technosol. The field experiment takes place on a setup consisting of 20 plots of 2 meters by 3 meters where the first 0.3 meters were disturbed and for half of them biochar has been incorporated (ca. 2% wt.). As we are expecting 3D effect on this specific field (effects of the limits of the plot, effects of the roots), we design a numerical study to determine the best experimental setup for a 2D ERT profile using pyGIMLi, an open-source software library for geophysical inversion.We conducted several numerical simulations to determine the optimal dimensions of a meshed body, which was considered as a semi-infinite space, to simulate profiles of 48 and 96 electrodes separated by 0.1 meters. Field measurements on plots with and without biochar showed electric resistivity values of 45 ohm m and 56 ohm m, respectively, suggesting that ERT might be able to detect the biochar presence. Using this information, we focus our numerical simulations on a suitable configuration to assess the effect of biochar onto root growth.