青海湖大气水溶性与颗粒态重金属的沉降特征及其对湖泊的输入

Investigating heavy metals in atmospheric deposition is critical to understand heavy metal cycling and to evaluate eco-environmental risk in remote areas. Based on three-year atmospheric bulk deposition samples collected monthly inside and outside Lake Qinghai from July 2012, in this project water-soluble and water-insoluble fractions are intended to being extracted from atmospheric deposition and concentrations of representative heavy metals in these two fractions determined respectively to: understand the characteristics of composition, pollution, and source of heavy metals in these two fractions, estimate their deposition fluxes and inputs to Lake Qinghai, investigate their seasonal/inter-annual and spatial distributions, discuss the role of atmospheric deposition in the accumulation of heavy metals in the lake water in combination with the inputs of heavy metals from major rivers into Lake Qinghai in previous studies, and quantify the contributions of atmospheric deposition to heavy metals in the lake sediment based on the accumulation flux of the modern lake sediment. The completion of this project will help us to understand the deposition characteristics of representative heavy metals in atmospheric deposition and their role in the accumulation of heavy metals in Lake Qinghai.

认识大气重金属的沉降特征对于理解偏远地区的重金属循环并评价其生态环境风险至关重要。本项目拟根据自2012年7月在青海湖4个地点按月采集的为期3年的大气总沉降样品，提取其水溶组分与颗粒物，并测试这两组分中典型重金属的含量，以查明青海湖大气总沉降中水溶性与颗粒态重金属的组成、污染及来源等特征，计算这两组分中重金属的沉降通量及其对青海湖的输入量，并探讨其季节与年际变化及空间分布；最后，结合前人研究中主要河流对青海湖重金属的输入，探讨大气沉降在该湖湖水重金属累积中的作用；结合湖泊现代沉积物中重金属的累积通量，估算大气沉降对青海湖沉积物重金属累积的贡献。本项目的完成将有助于认识青海湖的大气重金属沉降特征及其在湖泊重金属累积中的作用。

基于青海湖周边多个地点多年的大气总沉降监测得到，青海湖现代大气总沉降中颗粒物的平均年沉降通量为201.3 g/m2/yr，其中45%的颗粒物沉降发生在春季，其次是冬季占26.1%。大气总沉降中颗粒态和水溶性重金属含量的高值大多出现在每年的5-10月，这是由于显著增加的本地人类活动产生的大量人为污染物所造成的；然而，它们的沉降通量的高值却大多出现在每年的11-4月，这是由于冬春季节显著较高的大气总沉降通量所引起的。对于不同地点的重金属而言，布哈地点的大气总沉降中的颗粒态和水溶性重金属含量相对较低，这可能是因为该地点与其他两个地点相比更为偏远的原因。大气总沉降通过湖面每年直接输入青海湖的颗粒物的量为0.892×106 t/yr，对青海湖现代沉积物的累积贡献是45%。大气总沉降中颗粒态重金属的对青海湖现代沉积物中这些重金属累积的贡献大概为22.8-57.1%，平均为40.9%，暗示着大气沉降在沉积物着重金属累积的重要作用；而水溶性重金属的贡献显著较小（3.14-21.6%，11.5%），暗示着青海湖湖水中的重金属主要来自于河流的输入。