Surface water – groundwater connectivity implications on nitrate cycling assessed by means of hydrogeologic and isotopic techniques in the Alento river basin (Salerno, Italy): preliminary data

Luisa Stellato(a), Brunella Di Rienzo(a), Egidio Di Fusco(a), Mauro Rubino(a), Fabio Marzaioli(a), Vincenzo Allocca(b) Antonio Salluzzo (c), Juri Rimauro(c), Nunzio Romano(d) & Fulvio Celico(e)
(a) Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE), Dip. di Matematica e Fisica, Seconda Università degli Studi di Napoli, Viale Lincoln, 5, 81100 Caserta, Italy. E-mail: luisa.stellato@unina2.it (b) Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DiSTAR), Università di Napoli Federico II,Via Mezzocannone, 8, 80134, Napoli, Italy. (c) ENEA - Research Center of Portici, UTTP-CHIA, Environmental Chemistry Laboratory, Piazzale E. Fermi, 1, 80055 Portici (Napoli), Italy. (d) Dept. of Agriculture, Division of Agricultural, Forest and Biosystems Engineering, Università di Napoli Federico II, Via Università, 100, 80055, Portici (Napoli), Italy. (e) Interdisciplinary Centre for Studies on Water Resources, Department of Physics and Earth Sciences "Macedonio Melloni", University of Parma, Parco Area delle Scienze, 157/A, 43124, Parma, Italy.

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 and transport of nutrients in a riverine ecosystem at different spatial scales (from reach to catchment) becomes fundamental to understand the mechanisms regulating the concentration of nutrients, and in particular nitrates, in streams. The present work is developed 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". The main scope 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. In particular, the overall objectives of the proposed project are: i) the identification and quantification of spatio-temporal variation of the connectivity between groundwater and surface water; ii) the identification of the nitrate contamination sources of shallow groundwater; iii) 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. Here, the preliminary results of the hydrogeological, chemical and isotopic (222Rn, δ18O, δD) monitoring are presented and discussed.

Stream-groundwater interactions, alluvial aquifer, Italy, radon, environmental isotopes