Isotopic evidence for the impact of artificial snow on the nitrogen cycle in temperate regions

Abstract. As winters become warmer due to climate change, ski resorts around the world are increasingly and preferentially relying on artificial snow instead of natural snow. The chemical species contained in artificial snow can flow into the surrounding hydrological system along with melted snow, resulting in unexpected environmental pollution. This study is the first attempt to assess the impact of artificial snow on groundwater quality and its role in the nitrogen (N) cycle. Although numerous multi-isotope approaches exist for identifying sources and estimating the contributions to nitrate pollution, few studies have used nitrogen isotopes of nitrate (δ¹⁵N–NO₃⁻) and oxygen isotopes of water (δ¹⁸O–H₂O) simultaneously as tracers. This study aimed to evaluate the impact of artificial snow on the quality of surrounding groundwater at a ski resort, located in Mt. Balwang in Pyeongchang, South Korea (the 2018 Winter Olympics venue). Mt. Balwang, located in the upstream region of the Han River, is a critical source of water that joins major tributaries forming the upper Han River, which supplies drinking water to over 25 million residents in the metropolitan Seoul area. The average N contribution of mountain groundwater estimated using Bayesian mixing models was the highest from artificial snow (49.5 %), originating from manure and sewage, exceeding rainfall (31.6 %) and natural snow (18.7 %). These results are closely consistent with theoretical N loading rates, highlighting the potential for artificial snow to contribute to long-term N accumulation in alpine ecosystems. Our study highlights the importance of continuous monitoring to mitigate potential disruptions to the N cycle and preserve ecosystem stability as climate change increases dependence on artificial snow.