Chemical processes in the water cycle

Abstract

Features of the water cycle in nature, significant in the present context, are shown in Figs 3.1 and 3.2 in so-called box-model representations. The surface area of a basin is considered to be divided into two parts, a groundwater recharge area and a groundwater discharge area. The latter is usually found as strips along drainage channels and can vary in size depending on the basin discharge. Figure 3.1 refers to groundwater recharge areas. In both figures, the atmosphere and vegetation are represented as important parts of the water circulation. The root zone is considered as a separate entity because of its importance for water uptake by plants and for chemical and biological processes which at times can influence the chemistry of percolating water most markedly. The root zone may vary in depth from a few tenth’s of a metre to several metres, depending on the plant species that grow. The intermediate zone is also called the aerated zone by hydrogeologists and the unsaturated zone by soil physicists. Below this, there is the groundwater storage zone which can extend to considerable depths; in the figures it is called the saturated zone.