Modeling nutrient balances in a Mediterranean Basin: the Canale D'Aiedda case study (Apulia, Italy)

Agricultural activities and point sources are the main causes of nutrient pollution in most Mediterranean watersheds. To achieve the target of a sustainable water use by 2030, the next European Union environmental programs will increasingly be aimed at favoring implementation of alternative management practices. Member States will be called to identify within their national territory hotspots areas in which focus economic resources to improve their ecological status. At this aim, hydrological models represent a useful tool that can be used by stakeholders for watershed management. The Canale D’Aiedda watershed (Puglia, Italy) falls into the high environmental risk area of Taranto since the considerable concentration of industrial settlements and intensive agriculture. After a year of monitoring of streamflow, suspended sediment, nitrogen and phosphorous concentrations, the Soil and Water Assessment Tool (SWAT) was applied in order to identify hotspot areas within the watershed. The model calibration showed generally satisfactory results at daily scale for all the variables considered, taking into account some statistical indices like R2, Nash and Sutcliffe (NSE) and Percent Bias (PBIAS). Diffuse pollution sources, represented mainly by fertilizers, revealed as the main threat of the study area in terms of nutrient loads. Contrarily, point sources are important pressures for surface waters during the dry season, due to a limited dilution effect. Due to the karst nature of the soils, groundwater resulted the major receptor of nitrogen loads.