Nitrate concentrations and source identification in a Mediterranean river system

As most of the rural areas in Mediterranean Region, the Celone river basin (Apulia, Italy) is characterized by diffuse pollution from agriculture. Nutrient export from terrestrial ecosystem to the river is controlled by hydrological processes and nutrient input from point and non-point sources. In the present paper, anthropogenic nitrogen input and the riverine export of nitrate-N (N-NO3) were quantified through several survey campaigns, continuous measures of streamflow and discrete determinations of concentrations. A different frequency for water sampling was used, respectively, during floods and during normal- or low-flow state. Nitrate-N concentrations in surface waters were found to vary considerably across the seasons. The riverine N-NO3 export was estimated to be about 14 kg N ha−1 year−1. Major N inputs derived from fertilizers and animal manure correspond to 68.2 and 24 kg N ha−1 year−1, respectively. Nitrate-N fluxes in stream during flood events (21 days) accounted for about 63% of the annual loading. This study clearly demonstrates the importance of flood event contributions to the annual nutrient loading delivered to the reservoir and that more efficient fertilizers and management practices are needed to reduce N input.