SoilPlusVeg: An integrated air-plant-litter-soil model to predict organic chemical fate and recycling in forests.

Current modelling approaches often ignore the dynamics of organic chemicals uptake/release in forest compartments under changing environmental conditions and may fail in accurately predict exposure to chemicals for humans and ecosystems. In order to investigate the influence of such dynamics on predicted concentrations in forest compartments, as well as, on air-leaf-litter fluxes, the SoilPlusVeg model was developed including a forest compartment (root, stem, leaves) in an existing air-litter-soil model. The accuracy of the model was tested simulating leaf concentrations in broadleaf woods located in Northern Italy and resulted in satisfying model performance. Illustrative simulations highlighted the "dual behaviour" of both leaf and litter compartments. Leaves appeared to behave as "filters" of air contaminants but also as "dispensers", being deposition flux exceeded by volatilization flux in some periods of the day. Similarly, litter seemed to behave as a dynamic compartment which could accumulate and then release contaminants recharging air and vegetation. In just 85days, litter could lose due to volatilization, diffusion to depth and infiltration processes, from 6% to 90% of chemical amount accumulated over 1year of exposure, depending on compound physical and chemical properties. SoilPlusVeg thus revealed to be a powerful tool to understand and estimate chemical fate and recycling in forested systems.