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

Abstract

In order to identify the distribution of aluminium (Al) within an acid hillslope and its release to a stream, the spatial distribution of acid ammonium oxalate extractable Al (Al o ) and exchangeable Al 3 have been investigated on a podzolized hillslope in Bicknoller Combe, Somerset, UK. The eluviated Al from topsoils is mainly deposited in the lower soil horizons forming podzolic B horizons, but some Al flows downslope carried by lateral throughflow. Al oxides may provide the main source of exchangeable Al 3 on the study slope due to high soil acidity. Examination of the spatial distribution of exchangeable Al 3 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 Al 3 to the stream. Divalent base cations (Ca 2 and Mg 2 ), supplied from atmospheric input and organic decomposition and carried by throughflow, exchange Al 3 via cation exchange reactions under high water content. Laterally illuviated Al oxides in the lower hollow adjacent to the saturation wedge probably provide a pool for continuous delivery of Al either as soluble or complexed forms to the stream via the saturated wedge.

Heathland Restoration on Former Agricultural Land: Effects of Artificial Acidification on the Availability and Uptake of Toxic Metal Cations

“…However, in the current study there was no evidence that decreasing soil pH increased the extractable concentration of Al. This is in agreement with the weak relationship between pH and extractable Al concentration reported in the in the top (0-10 cm) of podzolic soils by other workers (Park & Burt, 1999;van Hees, Lundström, Danielsson, & Nyberg, 2001). Tyler (2004) found very low concentrations of Al in the 0.2 M HCl extractable fraction of the E horizon of podzols.…”

“…Consequently, the negligible effect of pH on the extractable concentration of Al may have reflected a relatively small pool of acid labile Al in the area of soil where the chemical amendments increased acidity. However, caution should still be applied when using such amendments, in case localised areas of preferential water flow lead to the acidified zone extending deeper into the soil profile (>40 cm), where there is a strong negative correlation between pH and Al mobility (Park & Burt, 1999;van Hees et al, 2001).…”

Shifts in discharge-concentration relationships as a small catchment recover from severe drought

“…Topics previously considered have included the following: the relationship between throughflow generation and the solute concentration of soil and stream water (Burt, ), diurnal variation in stream discharge and solute response (Burt, ), the use of mixing models to identify the contribution of throughflow in storm events (Anderson and Burt, ) and patterns of potassium export (Stott and Burt, ). Later, research at Bicknoller examined soil chemical processes and the delivery of solutes (including exchangeable bases, iron oxides, manganese and exchangeable aluminium) to the stream (Burt and Park, ; Park and Burt, , ; Park and Burt, ). The results presented here relate only to the data collected in the period August to December 1976 inclusive.…”