Salinity, nutrient and chlorophyll a vertical variations in the Ebro River plume

Abstract

Four water sampling campaigns in the Ebro River Plume were carried out, in spring, summer and autumn of 1999 and winter of 2000. In these campaigns salinity, nutrient and chlorophyll spatial distributions in the water column of river plume area were studied (where salinity values increase with depth). The sampling within the first meter of water column was carried out with a specifically designed device (SWAS). This device was designed by Dr. Jean Jacques Naudin to sample in the Rhone River Plume, although some modifications were introduced in the equipment to adapt it to Ebro River Plume conditions in order to obtain a very high vertical resolution in the sampling of the upper water column. Water samples could be acquired simultaneously at eight different depths (0.00, 0.05, 0.10, 0.20, 0.30, 0.50, 0.75 and 1.00 m) plus another additional at 5.0 meters. Salinity, concentration of ammonium, nitrite, nitrate, reactive soluble phosphorus (RSP), total dissolved phosphorus (TDP), total phosphorus (TP), ortosilicic acid and chlorophyll were measured in each water sample. The results of sample analysis allowed to obtain salinity profiles of this surface layer, clearly showing the reduced thickness of river plume when the sea is under low energetic conditions, with a sharp rise of salinity in the first centimeters of water column. Some discontinuities in this pattern were identified, specially when wind blew from the sea, introducing waters of higher salinity and temperature in the upper part of the water column. In most of the sampling stations, nutrient profiles showed a generally decreasing trend of their concentrations with the water depth, although several deviations of this pattern could be observed. These deviations were not due to freshwater load variations and many of them took place in the first 20 centimeters of water column. Since these variations in nutrient concentrations are not apparently related to freshwater loads and/or chlorophyll level changes, the origin of these variations could be planktonic organisms motions in this thin layer and activity changes due to these movements.