The distribution of solute processes on an acid hillslope and the deliveryof solutes to a stream: II. Exchangeable Al3+

In order to identify the distribution of aluminium (AI) within an acid hill slope and its release to a stream, the spatial distribution of acid ammoniu m oxalate extractable Al (Al-o) and exchangeable Al3+ have been investigate d on a podzolized hillslope in Bicknoller Combe, Somerset, UK. The eluviate d Al from topsoils is mainly deposited in the lower soil horizons forming p odzolic B horizons, but some Al flows downslope carried by lateral throughf low. Al oxides may provide the main Al3+ on the study slope due to high soi l acidity. Examination of the spatial distribution of source of exchangeabl e Al3+ on the study slope due to high soil acidity. Examination of the spat ial distribution of exchangeable Al3+ suggests that the slope hollow, where active convergent throughflow occurs, and the saturation wedge at the base of the slope are the main delivery routes of dissolved Al3+ to the stream. Divalent base cations (Ca2+ and Mg2+), supplied from atmospheric input and organic decomposition and carried by throughflow, exchange Al3+ via cation exchange reactions under high water content. Laterally illuviated Al oxide s in the lower hollow adjacent to the saturation wedge probably provide a p ool for continuous delivery of Al either as soluble or complexed forms to t he stream via the saturated wedge. Copyright (C) 1999 John Wiley & Sons, Lt d.