Nutrients behaviour in a stratified estuary: Ebro Delta case (Spanish text)

In microtidal marine zones, estuaries tend to be stratified, where the salt-wedge is located in the lower zone, which is clearly distinguished from superficial freshwater. The study area is a delta conformed by river Ebro which flows into Mediterranean sea. This estuary shows a strong saline stratification where two different water bodies with different salinity values and a transition zone exist. The transition zone, also known as halocline, is characterised by abrupt increase of salinity. The freshwater shows higher chlorinity toward downstream due to salt water entrainment. Also, discharges increases toward the mouth.; A gradual increment of salt in upper layer toward the mouth, and the abrupt increment in vertical direction cause the saline shock in freshwater phytoplankton as a consequence produces senescence and material drops to the river bed.; A new sampling technique has been proposed and developed. This sampling technique allows a higher resolution at halocline's samples. In that way a new zone of accumulation which is known as the interface can be well appreciated. This region acts as a filter where particles are retained temporally due to abrupt increment in fluid density. Also, it has been corroborated the presence of accumulation process in bottom salt-wedge. The particles coming from surface layer are settled down and swept in back upstream direction along the salt-wedge.; Senescent phytoplankton mineralization is a crucial process in order to determine vertical and horizontal distribution of parameters along the estuary. These parameters are: oxygen, pH, redox, ammonium, nitrite, nitrate, RSP, orthosilic acid, a chlorophyll and phytoplankton.; It has been established a dominant pattern in estuarine mixture for ammonium and RSP. The ammonium and RSP clearly show gains because of accumulation and mineralization of organic material at the interface and salt-wedge.; Nitrite and nitrate show important fluctuations in the pattern along location and sampling dates. These parameters showed gains, losses or conservative pattern.; The most frequent behaviour in orthosilicic acid is gains in saline region due to accumulation produced by salt-wedge.