Transport of Carbon and Nitrogen to the Northern Adriatic Sea by the Po River

Abstract

Concentrations of dissolved and particulate organic carbon (DOC, POC) and particulated nitrogen (PN) were measured in samples taken monthly for a year at two stations in the lower Po River and on four separate occasions in the mixing zone. From the results, the influence of suspended matter concentrations on POC and PN contents in the solid phase, and of flow variations on POC and PN contents in the water phase were evaluated. The behaviour of organic matter in the mixing zone was conservative in low to medium solid transport conditions, but had a strong negative deviation with respect to the dilution line during high solid transport, presumably due to both settling of particulate matter in the prodelta region and bacterial utilization of organic matter. Organic carbon was preferentially transported in the solid phase, in the lower Po, compared to world rivers in temperate zones. The loads of total organic carbon and nitrogen were estimated as 25·5×104and 15·5×104tonnes year−1respectively, making this river the most important contributor of organic matter and nutrients to the Mediterranean. These high loads together with lesser inputs from other Italian rivers flowing in to the northern Adriatic exert a significant impact on the productivity and trophic dynamics of this basin.