| 其他摘要 | During the last recent years, the isotopic geochemistry of copper and zinc has experienced a rapid development. As new isotopic tools, copper and zinc isotopes have been widely applied to different aspects of geochemistry like ore deposit, paleoceanography and biology, nevertheless the study of copper and zinc isotopes in lacustrine ecosystem remains poor. In lacustrine environments, for many years, the transport, transformation and cycle of heavy metal have retained the attention of geoscientist，but these researches are mainly confined to the determination of the concentration and speciation of heavy metal. To fill this gap, distribution of copper and zinc isotopes in lake were investigated in this dissertation and the factors controlling copper and zinc isotopes composition were discussed in the aim to establish the base for copper and zinc isotope geochemistry for tracing heavy metal in lacustrine ecosystems.
The optimal separation conditions of copper and zinc from environment samples (sediment, plant and suspended particulate material) are studied throμgh a series of experiments. Thereafter, the Hongfeng Lake and Aha Lake were chosen as study area, profile characteristics and seasonal variation of copper and zinc isotopes of the SPM (suspended particulate material) in the two lakes and their main branches were studied. Moreover, the speciation and cycle of heavy metal such as Cu, Zn, Mn, Ni, Co, Cr, Cd and Pb were studied. Several conclusions can be drawn from this thesis and are summarized here:
1. The optimal separation condition of Cu and Zn from environmental samples are described here. AG MP-1 resin (100-200 mesh) was used as anion exchange resin and 7 mol/L HCl + 0.001% H2O2, 2 mol/L HCl+ 0.001% H2O2, 0.5 mol/L HNO3 were used as eluants, and then the fitted volume of eluants were collected respectively. This procedure can effectively separate Cu and Zn from sediments, plants, and suspended particulate matter (SPM) samples with a recovery yield close to 100% that minimizes the isotopic fractionation during the chemical separation enoμgh to be neglected.
2. The variations of Cu isotopic composition of SPM and biological material in Hongfeng Lake, Aha Lake and their main branches range over 3.75‰ from -2.64‰ to 1.11‰。The δ65Cu of SPM in Hongfeng Lake range from -0.08‰ to 0.25‰, and the δ65Cu of SPM in its main branches range from 0.13‰ to 1.11‰ in summer while the δ65Cu of SPM in Aha Lake range from -0.62‰ to 0.37‰, and the δ65Cu of SPM in its main branches range from -1.08‰ to 0.60‰ in summer. For the two lakes, the copper isotope composition of SPM in winter is lighter than in summer. Furthermore, the copper isotope composition in biological material is much lighter and ranges from -1.54‰ to 0.03‰.
The profile characteristic of δ65Cu of SPM in Hongfeng Lake is ascribed to absorption by algae in summer, while the copper isotope composition in Aha Lake is mainly controlled by the water inputs from the catchment. These results sμggests that δ65Cu can be used as a good tracer of source materials in oligotrophication Lake(Aha Lake), while δ65Cu will be a new tracer for biologic activity in eutrophication Lake(Hongfeng Lake). Moreover, the vertical variation of temperature may be another significant factor affecting the copper isotope composition.
3. The variations of Zn isotopic composition of SPM in Hongfeng Lake and its main branches range from -0.29‰ to 0.26‰ and from -0.04‰ to 0.48‰, respectively while in Aha Lake and its main branches δ66Zn, they range from -0.18‰ to 0.27‰ and from -0.17‰ to 0.46‰, respectively, indicating that the SPM collected in their branches are enriched in heavy isotope. Zinc isotopic compositions in biological material show a larger variation and range from -0.35‰ to 0.57‰ illustrating that different materials from lacustrine ecosystem have unique isotopic signatures.
The δ66Zn variation versus chlorophyll contents shows positive correlation (R=0.97) in Hongfeng Lake in summer, which can be most likely ascribed to the processes of adsorption or absorption of zinc onto algae. At the opposite, the zinc isotope composition in Aha Lake is mainly controlled by the water inputs from the catchment, hence the zinc isotope composition can be used as a good tracer of source materials. In addition, the zinc isotopes ratio of SPM in Hongfeng and Aha Lakes in summer are lower than in winter, sμggesting that the atmospheric deposition might have been another significant source of lighter zinc isotopes. Moreover, the variation of δ66Zn values in biological material is wider than in SPM, implying that inorganic processes controlling zinc isotope fractionation should be of second-order importance compared to biological factors.
4. The concentration of heavy metal such as Mn, Ni, Co, Cr, Cd and Pb in South Lake is higher than in North Lake, mainly caused by the inputs from the Yangchang River and seasonal variations in concentration of heavy metal are mainly affected by seasonal fluxes variation. Furthermore, dissolved Mn, Ni and Cr show seasonal variations, which can be ascribed to the seasonal changes of “oxygenic” and “anoxic” conditions at the water-sediment interface. At last, during the water-particle interaction process, DOC, FeO, MnO and algae reproduction induce variation of heavy metals speciation. |
修改评论