鸭绿江口重金属沉积记录的环境意义

对采自鸭绿江主汊道的3根柱状样进行了放射性测年、粒度和重金属含量等指标的测试.通过放射性元素测年,得出其沉积速率分别为1.88、1.60和1.48 cm·a~(-1),由此建立年代框架.重金属垂向分布、R型聚类、地累积指数及沉积通量的分析结果表明,鸭绿江主汊道沉积的8种重金属的垂向分布具有阶段性,1981年前后(3个柱状样分别对应62、58和44 cm处)是重要的时间节点.R型聚类显示出3类物源,元素Zn主要来源于人类活动,Cr、Cu和Pb具有人为和自然双重来源,Cd、Hg、As和Ni主要来源于陆源物质的风化.主汊道重金属的含量总体上在逐年缓慢增加,但由于主汊道受到强大水动力的稀释作用,使其对鸭绿江口生态环境的影响很小,绝大多数重金属元素的地累积指数为-1.15~1.01,为无污染和偶有轻微污染的状态.受区域物源供给的限制,各重金属元素沉积通量在多数时段接近或低于背景值,总体上人类活动对鸭绿江主汊道重金属的沉积影响不大.鸭绿江的不同区域重金属的沉积记录并不同步,主汊道的重金属污染程度显著小于西汊道.

Environmental significance of heavy metals in the core sediments of the Yalu River estuary

Three sediment cores were collected from the Main Branch of the Yalu River estuary at depths of 108 cm, 160 cm, and 132 cm. For each core, radioactive dating was performed and the content of eight targeted heavy metals and the granularity were measured. The ages of the cores were determined based on the radioactive dating, and the sedimentation rates were 1.88, 1.60 and 1.48 cm·a^-1. The environmental significance of the heavy metals in the Yalu River estuary was explored by analyzing the vertical distribution, R-type clustering, geoaccumulation index, and anthropogenic fluxes of the heavy metals. The results indicate that the vertical distribution of the eight heavy metals displayed periodical characteristics and the key time node was all around the year 1981 (at the depth of 62, 58 and 44 cm for the three cores). The R-type cluster results show three kinds of material sources, Zn came from human activities, Cr, Cu, and Pb were attributable to both natural and anthropogenic sources, and Cd, Hg, As, and Ni came from weathering terrigenous materials. The content of the heavy metals in the main branch increased gradually, however, pollution had little influence on ecological environment because of dilution brought by the strong hydrodynamic force in the Main Branch. The most geoaccumulation index of the heavy metals was -1.15~1.01, indicating no pollution with occasional slight pollution in the study area. When the source supply was limited, the sediment fluxes of the heavy metals were close to or below the background value and, generally, the influence of human activities on the heavy metals'' deposition in the main branch of the Yalu River was low. The sediment records of the heavy metals were not synchronous and the level of pollution in the Main Branch was higher than that in the West Branch.