The use of numerical flow and transport models in environmental analyses

This chapter provides an overview of alternative approaches for modeling water flow and contaminant transport problems in soils and groundwater. Special focus is on flow and transport processes in the variably saturated vadose zone between the soil surface and the groundwater table. The governing flow and transport equations are discussed for both equilibrium and nonequilibrium flow conditions, followed by three examples. The first example shows how one-dimensional root-zone modeling can be used to estimate short- and long-term recharge rates, including contaminant transport through the vadose zone. A second example illustrates a two-dimensional application involving drip irrigation, while the third example deals with two-dimensional nonequilibrium transport of a pesticide in a tile-drained field soil. Also discussed are alternative pore-scale modeling approaches that may provide a better understanding of the basic physical and geochemical processes affecting fluid flow and contaminant transport in saturated and variably saturated media

Modelling Exchanges: From the Process Scale to the Regional Scale

International audienceThis chapter shows how the knowledge on the processes of surface exchange and atmospheric fate of different pollutants from agriculture or with an impact on agroecosystems is factored into mathematical simulation tools. It also considers the complexity of the interactions involved, the quantities of matter exchanged between agroecosystems and the atmosphere, and the measurement methods used to quantify them. The resulting models, which range from highly local (plant, leaf …) to global scales, ultimately enable to assess the impacts of changes in agricultural practices or climate change on pollutant exchanges between the atmosphere and agroecosystems. We describe different modelling approaches at the process, field, landscape and regional scales with different integrative levels. Model results are useful to understand how different processes interact and to predict how different environmental conditions, future climate or agricultural practices affect air quality. Models can also help identify levers for emission mitigation and estimate their efficiency