Seasonal Biotic Processes Vary the Carbon Turnover by Up To One Order of Magnitude in Wetlands

Soil Organic Carbon (SOC) turnover t in wetlands and the corresponding governing processes are still poorly represented in numerical models. t is a proxy to the carbon storage potential in each SOC pool and C fluxes within the whole ecosystem; however, it has not been comprehensively quantified in wetlands globally. Here, we quantify the turnover time t of various SOC pools and the governing biotic and abiotic processes in global wetlands using a comprehensively tested process-based biogeochemical model. Globally, we found that t ranges between 1 and 1,000 years and is controlled by anaerobic (in 78% of global wetlands area) and aerobic (15%) respiration, and by abiotic destabilization from soil minerals (5%). t in the remaining 2% of wetlands is controlled by denitrification, sulfur reduction, and leaching below the subsoil. t can vary by up to one order of magnitude in temperate, continental, and polar regions due to seasonal temperature and can shift from being aerobically controlled to anaerobically controlled. Our findings of seasonal variability in SOC turnover suggest that wetlands are susceptible to climate-induced shifts in seasonality, thus requiring better accounting of seasonal fluctuations at geographic scales to estimate C exchanges between land and atmosphere

Modeling rainfall-driven transport of Glyphosate in the vadose zone of two experimental sites in North-East Italy

A vertical one-dimensional analysis of infiltration processes and mobility of a tracer (potassium bromide) and a glyphosate-based herbicide, both subjected to hydrological forcing, was performed. Glyphosate is a widespread herbicide whose potential harmfulness and mobility under hydrological forcing have not been fully understood yet. Here, the spatio-temporal evolution of the two compounds was monitored for one year in two experimental sites (Settolo - Valdobbiadene, Colnù - Conegliano), located within the production area of the Prosecco wine (Treviso, Italy). In each experimental site the activities were carried out on two 25 m2 plots located at distances of 50-100 m from each other. The interpretative analyses considered rainwater infiltration as the driving mechanism of the herbicide transport and allowed us to obtain the calibration of a one-dimensional hydrologic model in each monitored plot. Different scenarios of the tracer evolution were simulated considering the pedologic properties of the shallower soil layers, the status of the plant coverage and of the root apparati, leading to a satisfactory reproduction of the observations in both the experimental sites. Modeling the mobility of the herbicide, considering also the degradation to its metabolite AMPA, proved to be more challenging, due to the tendency of glyphosate to be adsorbed to the soil matrix rather than be dissolved in water and transported toward deeper soil layers. Nevertheless, the analysis of model results for tracer and herbicide, compared with in situ observations, suggests that the transport of the glyphosate can take place even when it is adsorbed to the soil, through the movement, triggered by intense precipitation events, of microscopic soil particles within preferential flow paths