How mangroves salinize the soil

A transient one-dimensional model of the vertical movement of water and salt in the mangrove root zone is investigated. This is an extension of a previous steady state model which assumed that the ability of the mangrove roots to take up water is uniformly distributed throughout the soil and that the root water uptake is reduced if there is nonzero salt concentration around the roots. We show how both the time dependent and steady state salinity profiles in the soil depend on the strength of the root water uptake, the depth of the root zone and the porosity of the soil. The withdrawal of fresh water by the mangrove roots leads to salinization of the soil in the root zone, and significant reduction of the transpiration of the mangroves. When a steady state is reached, the salt that is excluded by the mangrove roots must diffuse back to the surface against the flow of soil water towards the roots. For a root zone of finite depth, a finite difference numerical scheme is used to investigate the rate of salinization of the root zone, and the diffusion of salt into the region below the root zone.