Journal of Oceanography, Vol. 56 (No. 5), pp. 517-525, 2000
Kazufumi Takayanagi* and Charles Gobeil
Institut Maurice-Lamontagne, Ministère des Pêches et des Océans,C.P. 1000, Mont-Joli, Québec G5H 3Z4, Canada
(Received 5 October 1999; in revised form 26 February 2000; accepted 29 March 2000)
Abstract: The concentrations of dissolved aluminum (Al) in the upper St. Lawrence Estuary were determined during periods of high and intermediate river-discharge. Laboratory experiments simulating estuarine processes were also conducted in order to examine possible mechanisms controlling the Al distribution. During the high river-discharge, the Al concentration at river end-member was 1.63 mM and decreased exponentially with increasing salinity. An almost complete removal of dissolved Al was observed in the low salinity area up to 10 with an intensive removal in the turbidity maximum zone. Principal mechanisms responsible for the Al removal inferred from the laboratory experiments were flocculation and adsorption onto suspended particulate matter (SPM). During the intermediate river-discharge, the Al concentration was 0.72 mM at the river end-member and again decreased with increasing salinity. However, the removal was less pronounced, being only about 25%. Good fits with model predictions and laboratory experiments suggest that principal removal mechanisms were authigenic aluminosilicate formation and adsorption onto SPM. In the upper St. Lawrence Estuary, Al distribution is controlled by a combination of three removal mechanisms: flocculation, authigenic aluminosilicate formation, and adsorption. Each mechanism can become a dominant factor depending on the concentration level and speciation of dissolved Al in the river water.