太湖底泥疏浚的水环境质量风险性分析

采用基于因子分析的主成分分析法将五里湖的16个水质参数概括为5个主成分,研究了各主成分以及其综合主成分在疏浚前后的变化,并以此为依据就底泥疏浚对水环境质量的影响进行了评价.结果表明,疏浚过程中,五里湖疏浚区的综合主成分得分最高,为1.15,水质综合排名在最后,水体色度和污染指数(F1)也达到最高值5.0;同时对照区综合主成分得分以及水体污染和色度指数(F1,F2)也相应升高,水质质量明显下降;这说明疏浚运作具有促进表层沉积物发生再悬浮和扩散作用,以及沉积物中内源性营养盐和重金属离子的释放作用.采用Monte Carlo随机采样法,利用平衡分配模型模拟和预测了疏浚过程中悬浮沉积物中重金属离子释放的阈值,结果表明疏浚过程中大部分重金属离子由悬浮沉积物向水体中释放的风险性较高,可信度达到90%以上,尤其是重金属离子Ni²⁺以及非金属污染物As释放的风险性较大,其可能的释放量分别分布在各自地表水环境质量标准EQS的28.6%～+∞之间和34%～+∞之间,说明底泥疏浚具有导致五里湖水体环境质量短期恶化的风险.此外,Monte Carlo随机采样分析方法应用也许可为湖泊底泥疏浚生态风险评价提供一条新的途径.

Water quality risk assessment for sediment dredging operations, Wulihu in Taihu Lake

To assess impacts and risks of sediments dredging on water environmental quality of Wulihu Lake, the principal components analysis method and the Monte Carlo romantic sampling model were used. Five principal constituents of Wulihu Lake were generalized and defined by using sixteen water quality index data, and it was studied the characteristics of the variation of every principal component and the comprehensive component with sediment dredging. The result show that during sediment dredging the water quality of Wulihu Lake were more serious, and the values of the comprehensive component and the principal component F1 increased to the highest level, were 1.15 and 5.0, respectively. This indicated that sediment dredging had great impacts on the water environment of Wulihu Lake, including sediment re-suspension, water transparency decrease, release of the internal nutrients and heavy metal ions etc. The risk of heavy metal release from re-suspended sediments and its certainty level were assessed and forecasted with the equilibrium partitioning model and the Monte Carlo romantic sampling method. The results also suggested that during sediment dredging, most of heavy metal ions have a great risk of release from re-suspended sediments with the certainty level over 90%; especially for Ni2+ and As, the release levels of which were 28.6% to approximately +infinity of EQS and 34% to approximately +infinity of EQS, respectively. Thus, sediment dredging would cause a temporary risk of water quality deterioration in Wulihu Lake. Others, the application of Monte Carlo sampling model may offer a new tool to assess a potential risk of deteriorations in water environment with sedimentsdredging.