长江水体常量和微量元素的来源、分布与向海输送

基于2017年4～5月期间对长江干流与主要支流共20个站位的观测,结合多元数理统计对水体中溶解态常量和微量元素的空间分布规律、来源及入海通量进行了分析,并通过与世界其它河流的对比探讨了流域自然因素与人类活动等对长江水环境中常量与微量元素分布与输送的影响.结果表明,Cu、Zn、Pb、Cd和As是长江流域主要受人类活动影响的元素,在下游区域显著高于上游与中游(P 0. 05),且各元素在长江重庆段和汉江均有较流域其他河段高的浓度值,这些河段相对较高的重金属含量主要与人类活动强度密切相关.有趣的是,长江宜昌至武汉段各元素均出现了较低的浓度值,这很大程度上受三峡水利工程蓄水所产生的"滞留效应"所致.统计分析还显示Na、Mg、K、Ca、Fe、Mn、Co、Ni、Mo、Cr和V主要与各种岩石矿物的风化与侵蚀相关,Cu、Zn和Pb主要受工业、金属冶炼、矿物开采等人类活动的影响,而Cd和As则主要来源于农业生产活动.长江重庆段和汉江区别于长江流域其它河段,表明水体受人类活动影响比较严重,但长江流域重金属浓度水平整体低于世界其它重工业和农业发达区域的河流.由于长江径流量巨大,Cu、Zn、Pb、Cd与As的入海通量是长江口及其近海重金属收支与循环的重要一环,并可能对河口生态环境产生深远的生态学效应.

Sources, Distribution, and Fluxes of Major and Trace Elements in the Yangtze River

Surface water samples were collected from 20 sampling sites in the main stream and its major tributaries of the Yangtze River from April to May 2017. The concentrations of dissolved trace and major elements were analyzed to determine the spatial variation, source identification, and riverine fluxes using various multivariate statistical techniques, including correlation analysis, principal component analysis (PCA), and cluster analysis (CA) with the goal of determining the influence of natural factors and human activities, including the operation of the Three Gorges Dam on the distribution and loading of major and trace elements in the Yangtze River water environment. Spatial distribution results showed that Cu, Zn, Pb, Cd, and As were the major elements affected by human activities in the Yangtze River, and their concentrations downstream were significantly higher than those in the middle and upper reaches (P<0.05). All elements had fairly high concentration values in both channels of the Yangtze River mainstream in Chongqing city and Hanjiang River in Wuhan city, which were mainly related to the enhanced human activities. However, the low concentrations of multi-elements in the reach of the Yangtze River in Yichang were largely caused by the retention effect of Three Gorges Project on element transport, which decreased the riverine loadings of multi-elements. Principal component analysis (PCA) indicated that Na, Mg, K, Ca, Fe, Mn, Co, Ni, Mo, Cr, and V were mainly associated with the weathering and erosion of various rocks and minerals in the river basin. And Cu, Zn, and Pb were mainly affected by enhanced human activities, such as industrial wastewater, metal smelting, and mineral mining, whereas Cd and As were mainly related to agricultural activities. The spatial distribution of trace and major elements showed that concentrations of some elements in the Yangtze River channels were enhanced by human activities. Generally, the heavy metal pollution in the Yangtze River Basin was lower than that in other rivers of the world. However, the annual fluxes of Cu, Zn, Pb, Cd, and As could have far-reaching ecological effects on the Yangtze River estuary and offshore ecological environment.