Variations in concentrations of aqueous aluminium and other chemical species during hydrological episodes at Birkenes, southernmost Norway

Abstract

Concentrations of H +, aluminium species, total fluoride, silica, TOC, and major cations and anions were measured in stream- and soil water in the Birkenes catchment during base-flow and high discharge hydrological episodes from 1984 to 1986. Snow and meltwater were also sampled before and during the spring snowmelt seasons. During all the rainfall and snowmelt hydrological events for the five field periods analysed, the H + concentration increased with flow, whereas inorganic monomeric aluminium, Al i (including Al 3+), increased with flow only during episodes preceded by relatively low flow periods; during subsequent events Al i remained nearly constant or even decreased. Concentrations of Al i and H + in soil water sampled under saturated conditions were generally stable over time compared to the variations for these species in streamwater. The considerable fluctuations observed for chloride Cl − and sulphate SO 2− 4 concentrations illustrated that displacement of soil water occurred. The results confirm the importance of hydrological factors in determining episodic aluminium response. Large variations in the saturation indices show that equilibrium with either Al(OH) 3 (gibbsite) or Al 2Si 2O 5(OH) 4 (kaolinite, halloysite) cannot control aluminium concentrations in streamwater at Birkenes; the same is true for Al(OH)SO 4 (jurbanite) although the saturation index for this mineral is less variable. Most probably, different controlling mechanisms predominate in the different soil layers, producing different chemical signatures which are picked up in the stream to varying degrees depending on hydrological conditions.