Global warming is progressing more rapidly in the Arctic compared with other regions of the world, and the increasing temperature has caused gradual permafrost thaw, resulting in significant changes in hydrological processes. However, the quantitative contributions of different water sources to Arctic watersheds under ongoing climate change remain poorly understood. Therefore, this study aims to address this gap by applying a water isotope-based mixing model to better quantify the sources and pathways of water flow in permafrost-affected catchments. In this study, isotopic and chemical data were used to determine the water sources and flowpaths of the Sagavanirktok (Sag) River on the North Slope in Alaska (USA) in the summer of 2022. Results obtained using a Bayesian mixing model indicate that meltwater from permafrost ice wedges contributes 17.7% upstream and 22.2% downstream to the Sag River. At the upstream with a frozen active layer or transient layer (including seasonal intrasediment ice), lower active layer water (mineral-rich) and upper active layer water (organic-rich) accounted for 31.5% and 18.1%, respectively. By contrast, at the downstream, the contribution of active layer water was 26.9%, which was similar to that of the other sources. The sources and flowpaths of Arctic freshwater affect changes in the geochemical characteristics of the freshwater, which is channeled to the Arctic Ocean through major Arctic rivers. This study quantitatively assesses permafrost ice wedge melt in an Arctic basin and provides insights to facilitate investigations of hydrological processes and geochemical changes associated with climate change in Arctic water systems.

The insufficient taking into account of groundwater as a basis for implementing protection measures for coastal wetlands can be related to the damage they are increasingly exposed to. The aim of this study is to demonstrate the pertinence of combining hydrogeological tools with assessment of pollutant fluxes and stable isotopes of O, H and N, as well as groundwater time-tracers to identify past and present pollution sources resulting from human activities and threatening shallow groundwater-dependent ecosystems. A survey combining physico-chemical parameters, major ions, environmental isotopes (O-18, H-2, N-15 and H-3), with emerging organic contaminants including pesticides and trace elements, associated with a land use analysis, was carried out in southern Italy, including groundwater, surface water and lagoon water samples. Results show pollution of the shallow groundwater and the connected lagoon from both agricultural and domestic sources. The N-isotopes highlight nitrate sources as coming from the soil and associated with the use of manure-type fertilizers related to the historical agricultural context of the area involving high-productivity olive groves. Analysis of EOCs has revealed the presence of 8 pesticides, half of which have been banned for two decades and two considered as pollutant legacies (atrazine and simazine), as well as 15 molecules, including pharmaceuticals and stimulants, identified in areas with human regular presence, including rapidly degradable compounds (caffeine and ibuprofen). Results show that agricultural pollution in the area is associated with the legacy of intensive olive growing in the past, highlighting the storage capacity of the aquifer, while domestic pollution is sporadic and associated with regular human presence without efficient modern sanitation systems. Moreover, results demonstrate the urgent need to consider groundwater as a vector of pollution to coastal ecosystems and the impact of pollutant legacies in planning management measures and policies, with the aim of achieving 'good ecological status' for waterbodies.