Aluminium in the Rivers Esk and Duddon, Cumbria, and their tributaries

Aluminium concentrations in water have been measured at several points in time for more than 50 sites distributed along the Rivers Esk and Duddon, Cumbria, and their tributaries. Total aluminium (Al_total), inorganic monomeric aluminium (Al_inorg) and organic monomeric aluminium (Al_org) were measured using a modified Driscoll technique. Concentrations were found to vary with season (flow rate) and geographical variation was often high. High Al_inorg concentrations (200–300 μg litre⁻¹), associated with low pH levels, were commonly found in tributaries in the upper reaches of the valleys, at high flow rates, and in catchments containing little or no improved agricultural land. Two catchments in the Duddon valley appear to be affected by afforestation and had even higher levels of Al_inorg (400–600 μg litre⁻¹). Two catchments in Eskdale were sampled in more detail. It was found that water quality changed markedly after the tributaries flowed through improved pasture land. Al_inorg concentration fell and pH values rose. Those changes were associated with increased Ca concentrations, possibly the result of agricultural liming.