Carbonic calcium system, nutrients and total organic nitrogen in continental runoff to the Galician Rias Baixas, NW Spain

Abstract

Biogenic element levels in continental runoff and their behaviour during estuarine mixing are studied in the Galician Rias Baixas for the upwelling season (May-October). Alkalinity, calcium, both with average concentrations of about 350 mumol.kg-1, and reactive silica, with 105 mumol.kg-1, show near conservative distributions along the estuarine side of the rias. A good agreement was found between values obtained by direct measurement in the river and those calculated by extrapolation to zero salinity from the mixing diagrams. On the other hand, nitrate (10-40 mumol.kg-1) and mainly phosphate (1 mumol.kg-1) are strongly affected by the biological activity of benthic algae during estuarine mixing. TON and ammonium in the innermost parts of the Ria de Arousa are also determined. The levels and time variations of these variables are very similar between stations with different water bodies. They show a tendency to increase in time during summer (from 20 to 50 mumol.kg-1 for TON and from 15 to 25 mumol.kg-1 for NH4+) independent of the water body present in the column