Zn Isotopic Composition Variability in Glacier-Fed Alpine Rivers of the Northeast Tibetan Plateau: Response to Migration Processes and Anthropogenic Impacts

Elucidating the migration processes of zinc (Zn) is crucial for comprehending its influence on global biogeochemical cycling. However, significant gaps remain in the knowledge of these processes in glacier-fed rivers of the northeast Tibetan Plateau (NETP). This study determined the isotopic compositions (δ⁶⁶Zn) of dissolved and particulate Zn in three alpine rivers fed by the Laohugou Glacier (LHG), the Lenglongling Glacier (LG), and the Yuzhufeng Glacier (YG) in the NETP. Results show that the δ⁶⁶Zn of particulate Zn varies from -0.01 ± 0.04 to +0.97 ± 0.12‰, generally higher than that of dissolved Zn (-0.82 ± 0.06 to +0.19 ± 0.03‰). This suggests a migration behavior in which isotopically lighter Zn is enriched in the dissolved phase and isotopically heavier Zn preferentially adsorbs onto the particulate matter. Moreover, the δ⁶⁶Zn in the dissolved phase exhibits obvious spatial variation, with an upward trend from the LHG-fed river to the YG-fed river and subsequently to the LG-fed river. In contrast, this trend is less pronounced in the particulate phase due to an anomalously high δ⁶⁶Zn value (0.97 ± 0.12‰). This isotopic anomaly is primarily attributed to anthropogenic impacts. A comparison with global terrestrial aquatic environments emphasizes the unique response of Zn isotope variability in NETP glacier-fed rivers to both migration processes and anthropogenic impacts.