Sorption model for dissolved and particulate aluminium in the Conway estuary, UK

Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, Kd, which varies from 0.67 105 to 3.38 106 ml g 1 for suspended particle concentrations of 2e64 mg l 1. The Kd values in general decrease with increasing suspended particulate matter and this tendency termed the ‘‘particle concentration effect’’ is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for Kd values of 105, 106 and 107 ml g 1 with various values of a. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with Kd value 107 ml g 1 and C0 values 16 10 6 mg ml 1 and 92 10 6 mg ml 1. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.