Nutrients related to the hydrologic regime in the coastal lagoons of Viladecans (NE Spain)

This study presents the major water characteristics of the Viladecans coastal lagoons in the Llobregat Delta (NE Spain), and the interpretation of their functional relationships with freshwater discharges. Ranges of conductivity show that Murtra, Remolar and Vidala are strongly influenced by freshwater. A second group (Reguerons, Braç Vidala) is characterised by brackish water with intermediate values of conductivity. In contrast, the lower part of the water column of Remolar and Vidala is quite salty water. A permanent pycnocline is established causing meromixis. Finally in Sant Climent a great variation is observed from fresh to seawater. Nutrient inputs are related to freshwater discharges. The range of DIN/SRP ratios observed (0.1–71) shows that a great variety of biogeochemical processes take place in these lagoons. High DIN/SRP ratios occur in water masses receiving high freshwater discharges (Murtra, Remolar and Vidala surface). In contrast, low DIN/SRP ratios correspond to water masses (Reguerons, Braç Vidala, Sant Climent) receiving water discharges from the groundwater and to those in the lower part of the water column of Remolar and Vidala. The SRP and DIN concentrations of the water in Remolar, Vidala and Murtra are very high (higher than any other with similar morphological characteristics in Spain). However, the trophic state of Reguerons, Sant Climent and Braç Vidala is lower. The data presented indicate that the Viladecans coastal lagoons are in a hypereutrophic state, as the result of receiving over a long period of time nutrient discharges associated to man-made freshwater inputs higher than their carrying capacity or capacity to metabolise the nitrogen and phosphorus discharges. Remedial measures should include reducing nutrient discharges into the lagoons and favouring water turnover in the lagoons.