The distribution of solute processes on an acid hillslope and the deliveryof solutes to a stream: I. Exchangeable bases

This paper aims to identify the spatial distribution of exchangeable base c ations in soils on an acid hillslope and to investigate possible cation rel ease processes from slope soils to the stream. The basic assumption underly ing this research is that the amount of exchangeable cations in soils refle cts the nutrient stores and cation leaching processes across the slope wher e vegetation and parent materials are similar. The distribution of exchange able Ca2+ Mg2+, K+ and Na+ has been investigated on a three-dimensional hil lslope on the Quantock Hills, Somerset, UK, A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable base s, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca2+ Mg2+ and K+, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate t hat the spatial distribution of major nutrient cations is tightly controlle d by the soil-vegetation system in nutrient-poor heathland environments. Na + is an exception to this vegetation controlled spatial distribution, becau se of its small involvement in the soil-vegetation and soil exchangeable sy stems. In subsurface soils, cations liberated from the soil-vegetation syst em are subject to redistribution over the slope according to the hydrologic al flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca2+, Mg2+ and Na+ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high fl ow. K+, however, shows an apparently different spatial behaviour, being def icient in the saturated wedge. Copyright (C) 1999 John Wiley & Sons, Ltd.