Nutrients behaviour in Ebro River plume (Spanish text)

The river freshwater, when it reaches the sea, flows above the saline water, thus a front, or plume, is formed. Its extension and morphology depends basically on the hydrodynamic conditions (river flow, tidal, waves and currents) determined in great measure on local winds.; This study has been carried out at the plume of the Ebro river. The spatial distribution of salinity, nutrients and chlorophyll a in the water column has been analyzed. The water samples were collected in different points of the plume every day during the sampling period. A device (denominated SWAS) that allows a water sampling of superficial layer with high vertical resolution has been used.; The salinity profile in superficial layer shows the reduced thickness of the plume under conditions of calm. An abrupt increase of salinity when the depth rises has been observed in the first centimeters of water column. The existence of discontinuities has been detected in this pattern, especially when marine waters of higher salinity are introduced to the upper layer by local winds.; The nutrients concentrations decrease gradually with increasing depth, chlorinity and fluvial influence. Nevertheless diverse deviations of this pattern exist in two different areas of the water column (surface and higher depth). These deviations are not caused by variations in continental contributions, but rather by the activity and movement of the planktonic organisms in these areas.; Two different behaviors are given in the mixture process. Nitrate and nitrite behavior are generally conservative, although some losses, mainly due to the absorption planktonic, take place. This consumption of planktonic communities causes that ammonium and RSP behaviors show losses, arriving RSP nearly to the exhaustion values in all the seasons since this nutrient is the limiting factor in this area. The orthosilicic acid generally behaves as the nitrate, although is more similar to RSP when important diatom blooms take place.; The system is basically determined for the fluvial discharges, especially in the case of high oligotrophia of the receptor marine ecosystem. Thus, a reduction of river flow and therefore of nutrients contributions could lead to significant effects in this coastal ecosystem.