Dissolved aluminum in four Chinese estuaries: Evidence of biogeochemical uncoupling of A1 with nutrients

Four Chinese estuaries, the Jiaojiang, Luanhe, Shuangtaizihe, and Yalujiang were investigated to determine A1 geochemistry and inter-relations between A1 and nutrients. These estuaries are characterised by low particulate organic carbon and high turbidity, with various tidal regimes. Dissolved A1 was determined by fluorescence method after liquid-liquid extraction into n-hexanol. Concentrations of A1 in the Luanhe estuary are relatively high (1.5-2.0 μM) and approximately uniform over the salinity range sampled, suggesting the influence of in situ sources/processes. In the Shuangtaizihe estuary, riverine concentrations of A1 (1.8-2.2 μM) decrease with higher chlorinity, indicating the predominance of simple dilution by seawater. The Jiaojiang and Yalujiang provide evidence that A1 is removed from water column at early stages of estuarine mixing, owing to probably the particle-solution reactions (e.g. flocculation) in the estuary. The A1 data are further compared with total suspended matter and nutrients in these estuaries. The data sets indicate that aluminum is not dominantly coupled to the cycle of nutrients.