The Isotopic (δ18O, δ 2H, δ13C, δ15N, δ34S, 87Sr/86Sr, δ11B) Composition of Adige River Water Records Natural and Anthropogenic Processes

Abstract

The water composition of the river Adige displays a Ca–HCO3 hydrochemical facies, mainly due to rock weathering. Nitrate is the only component that has increased in relation to growing anthropogenic inputs. The aim of this paper was to identify the origin of the dissolved components in this river and to establish the relationship between these components and critical zone processes within an evolving framework where climatic and human impacts are influencing the riverine system. In particular, emphasis is given to a wide spectrum of isotope data (δ18O, δ2H, δ13C, δ15N, δ34S, 87Sr/86Sr, δ11B), which is considered useful for determining water origin as well as natural and anthropogenic impacts on riverine geochemistry. Together with oxygen and hydrogen isotopes, which are strictly related to the climatic conditions (precipitation, temperature, humidity), the carbon, sulphur, strontium and boron signatures can describe the magnitude of rock weathering, which is in turn linked to the climatic parameters. δ13CDIC varies regularly along the riverine profile between −4.5‰ and −9.5‰, and δ34SSO4 varies regularly between +4.4‰ and +11.4‰. On the other hand, δ15NNO3 shows a more scattered distribution between +3.9‰ and +10.5‰, with sharp variations along the riverine profile. 87Sr/86Sr varies between 0.72797 in the upper part of the catchment and 0.71068 in the lower part. δ11B also shows a rough trend, with values approaching 7.6‰ in the upper part and 8.5‰ in the lower part. In our view, the comparatively low δ34S, δ11B, and high 87Sr/86Sr values, could be a proxy for increasing silicate weathering, which is a process that is sensitive to increases in temperature.