Sr isotope fingerprinting of multiple water-source characterizations and its environmental implications in a complex lake-groundwater system, Wudalianchi, Northeast China

The Wudalianchi UNESCO Global Geopark (Northeast China) is famous for its rare cold mineral springs and its associated five hydrologically connected barrier lakes. During this study, strontium (Sr) isotopes (87Sr/86Sr) were studied along with other geochemical data to determine the source of water within the region's deep and shallow mineral springs, shallow wells, and lakes. These waters were characterized by a relatively narrow range of 87Sr/86Sr ratios (0.70648-0.70816). Those ratios were not different in shallow and deep mineral spring waters, and probably reflect ratios associated with potassium volcanic rocks in the area as expected. When combined with 1/Sr ratios, it appears that the shallow mineral springs were derived from upwelling of deep mineral springs and had a composition as an endmember of other waters. Shallow mineral springs and wells exhibited large variations in Cl−/Sr2+ and NO3−/Sr2+ ratios, owing to the input of fertilizers. Farmland runoff and waters from Yaoquan Lake that drains an agricultural area also appear to have been influenced by fertilizers and showed 87Sr/86Sr ratios intermediate between wells and mineral springs. Sewage input is likely responsible for this difference and a slight elevation of the ratios in the wells. The Wudalianchi lakes had similar variations in 87Sr/86Sr and 1/Sr ratios, suggesting their rapid response to terrestrial runoff and the supply of shallow mineral springs. Strontium isotope data can be combined with water chemistry to emphasize water-rock interaction and refine the region's existing model of water interaction in surface and subsurface environments.