The impact of surface water - groundwater interactions on nitrate cycling in the riparian and hyporheic zones assessed by means of hydrogeologic and isotopic techniques in the Alento river basin (Italy): Preliminary results.

The knowledge of the mechanisms regulating the concentration of nutrients in rivers is of fundamental importance in maintaining the ecological functioning of streams. In particular, in the riverbed sediments, where the biogeochemical activity is enhanced, the study of retention mechanisms becomes crucial in order to determine the restoring capacity of a watercourse. In case of groundwater inflow, hot-spots in the recycling of nutrients within the riparian and hyporheic zones can be observed, influencing the nutrient load transported into the stream depending on retention mechanisms. Hence, the study of biotic and abiotic factors affecting retention within the riverbed sediments, and the study of processes occurring at the interface of groundwater and surface water (i.e., the hyporheic zone) are fundamental in understanding the mechanisms of retention and transport, which regulate the concentration of nutrients, and in particular nitrates, in streams. The main scope of the present project, within the framework of the IAEA Coordinated Research Project (CRP)“Environmental Isotopes and Age Dating Methods to Assess Nitrogen Pollution and Other Quality Issues in Rivers”, is to find a reliable methodology to, spatially and temporally, quantify groundwater inflows to a river in order to study nitrates contamination of a groundwater dependent river ecosystem. This goal will be achieved focusing on three main objectives: 1. The identification and quantification of spatio-temporal variation of the connectivity between groundwater and surface water in the considered river basin. 2. The identification of the nitrate contamination sources of shallow groundwater in the considered alluvial aquifer. 3. The study of the nitrates retention and recycling mechanisms in riverbed sediments in critical effluent river reaches (key sites) in order to determine the importance of hyporheic and riparian zones in the considered catchment. Here, the preliminary results of the hydrogeologic, chemical and isotopic monitoring are presented and discussed.