vadosetransport

Vadosetransport, commonly referred to as vadose transport, describes the movement of water, solutes, and gases through the vadose zone—the unsaturated region of soil and rock between the land surface and the water table. It governs how rainfall infiltrates, how contaminants travel toward groundwater, and how nutrients become available to plants. Understanding vadose transport is essential in hydrology, agriculture, and environmental remediation.

Its primary processes include advection driven by gravity and pressure gradients, capillary rise, and diffusive and dispersive spreading. Sorption to soil minerals and organic matter can retard solute movement; chemical reactions, biodegradation, and volatilization can transform or remove constituents. Transport is modulated by soil properties such as moisture content, pore structure, temperature, and heterogeneity, as well as by surface conditions and plant uptake.

Mathematically, vadose transport is often described by coupling Richards' equation for unsaturated flow with a solute transport equation that includes advection, dispersion, and sorption terms. Numerical models (for example HYDRUS) simulate moisture and solute profiles in one to two dimensions under varying boundary conditions, such as rainfall infiltration, irrigation, evapotranspiration, and root water uptake.

Applications include assessment of pesticide leaching, contaminant fate and transport in soils, groundwater recharge estimation, and design of vadose-zone remediation strategies. Data requirements encompass soil water retention and unsaturated hydraulic conductivity, sorption isotherms, dispersion coefficients, and reaction kinetics, typically obtained from laboratory experiments, field tests, and in-situ monitoring with sensors such as TDR probes.

Uncertainties arise from soil heterogeneity, nonlinear hydraulic behavior, and complex coupling with surface water and groundwater systems. Ongoing research aims to improve parameter estimation, scale up process representations, and integrate vadose-zone processes into watershed or groundwater models.