Predicting aqueous aluminium concentrations in natural waters

Abstract

Aluminium is a pH-sensitive element that can cause acute toxicity symptoms in some organisms at aqueous activities of 10 µM or less^1–3. Scientists working on agricultural systems have long been concerned with the deleterious effects of aluminium on crop roots^4,5. More recently, environmental scientists have reported a potentially harmful biogeochemical link between acidic deposition onto forest soils and aluminium toxicity in forest and aquatic communities of northeastern North America and northern Europe^6–8. Because of this general interest in aluminium toxicity as an environmental threat, there have been renewed efforts to model the chemistry and transport of aqueous aluminium in soils and surface waters. Here we propose that much of the spatial and temporal variability in aqueous aluminium chemistry can be accounted for by a two-component equilibrium model involving a solid-phase humic adsorbent and an aluminium trihydroxide mineral phase. Inputs for the model are solution pH, copper-extractable organic aluminium and the titratable carboxyl content of soil humus.