Geochemical Characteristics Of Particulate Metal Elements And Their Comparison In The Changjiang Drainage Basin And The Lower Reach Of Huanghe

As the product of rock’s weathering, suspended particulate matters （SPM） carrythe information of climate change of the Drianage Basin. And the particulate mattercan also adsorb heavy metals polluted by human activities in the water column.Particulate samples were collected from Changjiang drainage basin（mainstream andmajor northern and southern tributaries）during August to October2009; from thelower reach of Huanghe （Lijin station）monthly from April2010to November2011and also daily during the water-sediment regulation event in June-July2009andnatural flood in August2010; from the coastal area of Huanghe Estuary before, duringand after the water-sediment regulation event in2009. The characteristics ofgeochemical composition and the pollution status of heavy metals in the Changjiangdrainage basin and the lower reach of Huanghe are discussed in this thesis.The chemical index of alteration （CIA） of SPM in the main stream of Changjiangvaries from60to80and increases from the upstream to the downstream, whichindicates that the rock is subjected to moderate chemical weathering and the degree ofrock weathering increases from upstream to downstream. The range of CIA valuereflects a warm and wet climate in the study area. The CIA value of SPM in thenorthern tributaries varies from61to80with a mean value of66, while it varies from64to81in the southern tributaries with a mean of71. It can be seen from theA₂O₃-（CaO+N₂O）-K₂O diagram that the concentrations of Ca and Na decreases andK increases little with the increaseing of CIA, which indicats the Ca-bearing andNa-bearing plagioclase is dissolved and the K-bearing feldspar is stable during theweathering of rocks.The CIA value of SPM in the Huanghe downstream （Lijing Station） varies from60to72with a mean value of68, which is lower than the Changjiang. The degree of rock’s weathering in the Huanghe drainage basin is affected by runoff and temperature.A simple model is used to combine the CIA and sediment yield. It can be seen fromthe model that the actual sediment yield in main tributaries of Changjiang is lowerthan its theoretical value. There wasn’t seriously water and soil loss in the Changjiangdrainage basin due to the storage of lake, intercepting by huge dams and vegetation’sconverage. The sediment discharge in the Huanghe is similar with the theoreticalvalue predicted by model recently, mainly due to the decreasing of riverine runoff,construction of dams and implementation of water-soil conservation.The concentration range of particulate heavy metals （Cr, Cu, Ni, V and Zn） in themain stream of Changjiang were75.16¹54.67mg/kg,22.86¹68.35mg/kg,37.28⁷8.79mg/kg,100.27²12.06mg/kg,89.19⁶31.65mg/kg respectively. Theconcentrations of heavy metal increase from Jinshajiang to Wanzhou with highestvalue appeared at Yichang station. The distributions of heavy metals in the middle anddownstream of Changjiang are stable. The normalized concentations of heavy metalsstill increase from Jinshajiang to Wanzhou, which indicate that this increasing trend ismainly due to the different bedrock in the drainage basin. The normalizedconcentrations of heavy metal are highest in the Three Gorges Dam （TGD） area whichillustrate the effect of sewage discharged from Yibing to Yichang. The distributions ofheavy metals were stable in the middle and downstream which indicate that thevariations of heavy metals are mainly influenced by grain-size. The concentrations ofheavy metals （Cr, Cu, Ni, V and Zn） in the northern tributaries ranged from93.19²32.60mg/kg,34.56¹18.43mg/kg,41.92¹08.43mg/kg,132.58¹98.79mg/kg,152.79⁶16.54mg/kg. The concentrations of heavy metals in the southerntributaries were75.97³50.00mg/kg,52.29²16.00mg/kg,41.17¹00.00mg/kg,105.91⁵58.00mg/kg,269.89⁴715.57mg/kg, respectively. Enrichment factors （EF）of heavy metals were calculated to evaluate the degree of contamination. Cu and Znwere moderate polluted in the main stream of Changjiang. Cr, Cu, Ni and Zn weremoderate polluted in the northern tributaries, Zn was significantly polluted and Cu, Cr,Ni and V were moderate polluted in the southern tributaries. The heavy metalpollutions in the southern tributaries were mainly caused by mining activity due to its abundant resources of metal mineral in the drainage basin.The concentrations of heavy metals in the Huanghe downsteam （Lijin） werehigher in winter, lower in summer and the lowest value appeared during the water andsediment regulation. However, the calibrated concentrations of heavy metals werestable between different seasons after normalized by Al, which illustrate that thevriations of heavy metals are mainly influenced by grain-size. During the water andsediment regulation in2009, the concentrations of heavy metals decreased at thebeginning and then increased. However, different variation was found during naturalflood caused by rainfull inAugust2010. It can be seen from the EF factor that Zn wasmoderate polluted in the Huanghe estuary and Cr, Cu, Zn was moderate polluted inthe coastal area. Three factors can explain the geochemical conposition of SPM inHuanghe estuary, which are chemical weathering, rock type and anthropogenicimpact.The particulate concentrations of rare earth elements （REEs） in ChangjiangBasin was120²40mg/kg with a mean value of157mg/kg, which is close to thelower limit of the global sediment concentration. The chondrite-normalized pattensshow that the light rare earth elements （LREEs） were significantly enriched. There areno obvious Ce anomalies with weak Eu depletion. The NASC-normalized patternsbecome less variable, with weak Eu-depletion. The concentrations of REEs inHuanghe estury were136.10¹94.13mg/kg. The chondrite-normalized pattens showthat the LREEs were enriched while the NASC-normalized patterns were less variablein the Huanghe estuary.