Seasonal Dynamics of Amorphous Silica in Vantaa River Estuary

In order to understand the importance of amorphous silica (ASi) in transport of bio-reactive Si from catchment areas to the seas in northern anthropogenically influenced catchments, we investigated the seasonal evolution of ASi concentrations and load patterns together with environmental variables along the Vantaa River estuary in southern Finland during one year. A clear seasonal variation was observed in the ASi dynamics of the river with highest loads during spring, when 79% of the yearly ASi load was discharged. The main reason for this appeared to be the high discharge of the river and concomitant high load of ASi. About 38% of the annual bio-reactive Si load of the river consisted of ASi. The ASi concentration in the river varied from 11 to 192 \(\upmu \)mol L. About 3% of the ASi load accumulated in the sediments of the estuary. The role of ASi in the riverine transport of bio-reactive can be very important in northern agricultural catchments and phytoliths probably play a significant role in the transport of ASi from catchment areas to the sea.