Using Radon-222 as a Naturally Occurring Tracer to investigate the streamflow-groundwater interactions in a typical Mediterranean fluvial-karst landscape: the interdisciplinary case study of the Bussento river (Campania region, Southern Italy).

The Bussento river basin, located in the south-east of Campania region, shows interesting issues related to water assessment and management. Complex interactions and exchanges between surface and groundwater exist, influencing also on-shore and off-shore submarine springs. Therefore, gaining river segments from karst groundwater and losing river segments towards the aquifer are recognized. Groundwater protection for drinking domestic use, riverine wild-life conservation and coastal water quality require a progressively optimized knowledge of these interactions. As a support for hydrological modelling tasks, various measurement campaigns have been made along the Bussento river for the acquisition of data about Radon concentration in the river and spring waters, using a radon monitor, Rad7 (Durridge Inc.) , equipped with a water probe and a Rad7H2O to measure radon activity concentration in water. The aim of this preliminary study is to perform an useful methodology for the localization of the contributions of the groundwater along the riverbed, and for their proportional assessment compared with the superficial back return flow.