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

Abstract

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 (greater than 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, K sub(d), which varies from 0.67x10 sup(5) to 3.38x10 sup(6) ml g sup(-1) for suspended particle concentrations of 2-64 mg l sup(-1). The K sub(d) 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 10 sup(5), 10 sup(6) and 10 sup(7) ml g sup(-1) with various values of alpha. 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 10 sup(7) ml g sup(-1) and C0 values 16x10 sup(-6) mg ml sup(-1) and 92x10 sup(-6) mg ml sup(-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.