Nutrient sources and dynamics in a mediterranean fluvial regime (Ebro river, NE Spain) and their implications for water management

Nonpoint source and point source nutrient loads (N, PO4-P, COD) to the Ebro River in its central sector were estimated using hydrogeological and socioeconomical data. Their impacts on eutrophication and nutrient dynamics in the river were analyzed through a review of the public administrationʹs historical data and the interpretation of two sampling profiles in September 02 (low flows season) and April 03 (high flows season). A marked seasonality was found in nutrient concentrations, nutrient loads and eutrophication indicators (O2, Turbidity), appearing symptoms of eutrophication during the summer related to both NPS and PS Nutrient loads within the study area. Agricultural NPS account for 64% of NO3 loads generated within the study area while urban and industrial PS are responsible of 88% PO4-P and 71% COD loads. Biological reactions within the river ecosystem (including denitrification in the most eutrophic branches) were found to be a key factor in nutrient content and dynamics.