| 其他摘要 | Water is not only indispensable to the survival of humans and all living things, but also an important natural resource to industry and agriculture. As a natural porter, it plays a key role on mater cycles. Rivers are important part of water, supplying fresh water for human, which are also main channels for the exchange of substances and energy between the continent and the ocean. River erosion is an important geochemical process, which promotes rock weathering and subsequently releases large amount material, providing necessary material for the terrestrial ecosystems. Meanwhile, this process accompanied by atmospheric CO2 drawn down regulates the global climate. Hence, it is meaningful to focus on river erosion for us understanding mater cycle, lone-time carbon cycle and climate change mechanisms. In recent years, for the development of technology and improving of analytic ability, many stable isotopes have been applied in river erosion. Among these, Mg is a new tool and it makes great progress in the study of geochemical processes. Previous study have shown that variation of Mg isotopic composition is linked to many factors, such as source lithology, secondary processes associated with hydrogeological condition. Accordingly, we can get important information of chemical weathering or hydrogeological characteristic from Mg isotopic composition. Huanghe River is the second largest river in China in terms of drainage basin and river length，and the largest one in transporting material to sea in the world. The river traverses through the Chinese Loess Plateau, which is easily weatherable, the river erosion is very active in this areas. For this, the river carries a large amount of suspended load. And the Chinese Loess plateau is very sensitive to the climate change. So we can get much important information from geochemical study of Huanghe River. Based on these, Huanghe River was chose for study. we used a synoptic-sampling approach from upstream to downstrean in July, 2012. The major element，HO, Sr, sulfur and magnesium isotope of water samples were analyzed, meanwhile Magnesium isotope composition of suspend load was also measured for several samples. Results showed that: 1, The Huanghe River chemical composition is controlled by hydrogy, climate and geology in the basin, the influece from human activity also cannot be neglected. 1） The river water of Huanghe River is alkaline. In comparison with other major rivers, almost all the major element showed higher content. For the Huanghe River main channel, the chemical composition change from Ca + HCO3 in the upstream samples to Na + Cl + SO4 in the downstream areas. Cationic composition of upstream samples are mostly dominated by Ca with an order of Ca > Na > Mg > K, except for two Na-dominant samples (sites MH01, MH02) taken from headwater tributaries, accounting for 47% of all the cations. Sodium is the dominant cation in the midstream and downstream, with Na > Ca > Mg > K, accounting for 53%. Bicarbonate (HCO3) is the dominant anion for all water samples, accountingfor 70% of the TZ in the upstream samples, 54% for the midstream, 49% for the downstream. Cl and SO4 are also important anions, accounting for over 40% of the anions for most of the samples. 2） The H、O isotope compostion of river water indicated that precipitation is the main source of Huanghe River water, and the basin suffered from strong evaporation. 3） The Sr isotope ratio（87Sr/86Sr）of the Huanghe River is low, with a narrow range of 0.710-0.723, close to the value of marine carbonate. In general, there is an increasing trend from upstream to downstream. While the range of sulfur isotopes present a wide range(-3.65~18.85‰)，and have a general increase with SO42- concentration，reflecting the significance of evaporates dissolution. 4） The high TDS in the river is predominant controlled by evaporite dissolution, the irrigation return water has a significant influence on river TDS in some area |
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