Inorganic aluminium-hydrogen ion relationships for acidified streams; the role of water mixing processes

Abstract

Streamwaters draining acidified catchments usually exhibit large fluctuations in aluminium and hydrogen ion concentrations which are positively correlated with flow: stormflow waters are mainly derived from waters passing through the upper acidic and aluminium bearing soil zones; baseflow waters are derived from the lower soil/groundwater zones where inorganic reactions prevail and hydrogen ions generated in the upper soil horizons are consumed. In several cases these variations in streamwater chemistry cannot be explained by solubility control of a single mineral phase such as microcrystalline or natural gibbsite. Here, for three such catchments, the controlling mechanisms are explored in terms of both conservative and non-conservative two-component mixing of upper soil and ground waters. For this exercise linear concentration plots are the best tools; the commonly used log-log plots lead to a confounded picture masking important insights.