Aerial inputs of pollutants to the Severn Estuary
1994
Vale, J. A. | Harrison, S. J.
Pollutants deposited on the Severn Estuary from the atmosphere derive mainly from local industrial and urban centres. Atmospheric deposition accounts for 50% of the lead and zinc inputs, 10–20% of the cadmium, copper and nickel to the Estuary, but only a small proportion of the chromium, iron and manganese. Most of the cadmium, copper and lead comes from the lower atmosphere near Avonmouth and Cardiff Bay. Westerly winds have much higher sodium and chloride concentrations but generally carry lower pollution loads than the less frequent, offshore easterlies. Strong winds recycle pollutants into the atmosphere via sea spray. The hills on both sides of the Estuary encourage deep vertical mixing, and effluents may be carried well inland. Stable atmospheres, associated with southerly and easterly airflows, cause trapping and entrainment of stack emissions. Thus easterlies may deposit much higher levels of pollutants. This paper reviews present knowledge regarding the deposition of metals from the atmosphere into the waters of the Severn Estuary. Preliminary results (1989) indicate that, while distribution patterns remain broadly similar, the quantities deposited were considerably less than they were six years previously.
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