喀斯特高原湖泊生物地球化学过程中的锌同位素特征

Zinc isotope characteristics in the biogeochemical process of karst plateau lakes

采用多接收电感耦合等离子体质谱仪（MC-ICP-Ms）对喀斯特高原湖泊红枫湖、阿哈湖水体及其主要支流水体悬浮物和一些生物样品中的锌同位素进行了测定，测试精度小于0．11％。（2SD）。结果显示，红枫湖水体与其主要支流水体悬浮物中的δ^66Zn变化范围分别为-0.29‰～0.26‰和-0.04‰～0．48‰，阿哈湖水体与其主要支流水体悬浮物中的δ^66Zn变化范围分别为-0．18‰～0．27‰和-0．17‰～0.46‰，均表现出支流中的锌同位素组成较重的特点。两湖生物样品中的δ^66Zn变化范围较大，为-0．35‰～0．57‰，说明湖泊生态系统中各端员的锌同位素组成存在一定差异。根据同位素组成分析，湖泊主要入湖河流及所携带的陆源物质是阿哈湖？白水体中锌的主要来源，锌同位素是一种较好的物源示踪工具。红枫湖夏季δ^66Zn与Chla（叶绿素）呈显著的正相关（R=0. 97），主要是藻类对锌的有机吸附和吸收过程导致锌同位素组成发生变化。此外，湖泊水体悬浮物中的锌同位素组成均在夏季较轻，表明大气的干湿沉降可能是一个较负的锌同位素源。水体悬浮物中的δ^66Zn变化范围小于生物样品中的δ^66Zn变化范围，说明由于生物作用过程导致的锌同位素分馏大于非生物过程。

The Zn isotopic compositions of SPM （suspended particulate materials） and biological samples from the Hongfeng Lake and the Aha Lake as well as their main branches were analyzed with multiple collector inductively coupled plasma-mass spectrometry. The results show that the variations in Zn isotopic composition of SPM in the Aha Lake and in its main branches are -0.18‰--0.27‰ and - 0.17‰-0.46‰ respectively, while the variations in the Hongfeng Lake and in its main branches are - 0.29‰- 0.26‰ and -0.04‰--0.48‰ respectively, indicating that the heavy zinc isotopes are enriched in the SPM in their branches. The zinc isotope compositions in biological material show a larger variation from - 0.35‰ to 0.57‰, suggesting that different materials from the lacustrine ecosystem have their respective unique isotopic signatures. It is shown that the zinc isotope composition in the Aha Lake is mainly controlled by the water inputs from the catchment, and hence the zinc isotope composition can be used as a good tracer of source materials. It is also found that δ^66Zn variation versus chlorophyll contents shows positive correlation （R = 0.97） in the Hongfeng Lake in summer, which can be probably ascribed to the process of adsorption or absorption of zinc onto algae. In addition, the zinc isotope ratio of SPM in the Hongfeng and Aha Lakes in summer is lower than that in winter, implying that the atmospheric deposition might have served as another significant source of lighter zinc isotopes. Moreover, the variation of δ^66Zn values in biological material is wider than that in SPM, indicating that inorganic processes controlling zinc isotope fractionation should be of subordinate importance compared with biological factors.