乾务水库表层沉积物氮磷和重金属时空分布特征与生态风险评价

为了解乾务水库表层沉积物中的环境质量状况，于2019年丰、枯两季（8月和10月）对库区6个采样点的氮磷营养元素和8项重金属进行了监测，采用综合污染指数法、地累积指数法及潜在生态风险指数法开展生态风险评估和溯源分析。结果表明：乾务水库表层沉积物中TN和TP浓度在丰、枯水期的平均值分别为2 010和433、1 873和308 mg/kg，且总体呈现库中高、南北两端低的时空分布特征。综合污染指数评价结果表明，乾务水库整体TN为重度污染，TP为轻度污染。乾务水库表层沉积物中Hg、As、Cr、Mn、Ni、Cu、Zn和Pb的平均浓度分别为0.22、10.64、30.97、293.25、17.51、21.01、102.65和55.32 mg/kg。时空分布方面，除Mn和Zn外，其他重金属在丰水期污染相对枯水期较重；受水库地形和季节性调水影响，除Mn和Pb外，其他重金属浓度水平在丰水期均表现出库首至库中区域（Q3和Q4采样点）为高值区，库中至库尾区域（Q2和Q3）在枯水期则为高值区。地累积指数法及潜在生态风险指数法评价结果均表明，Hg为主要的生态风险贡献因子，贡献率达75.8 %，库区综合潜在生态风险等级总体为中风险。

Spatiotemporal distribution characteristics and ecological risk assessment of nitrogen,phosphorus and heavy metals in the surface sediments of Qianwu Reservoir

To understand the environmental quality of the surface sediments of Qianwu Reservoir in wet and dry seasons (August and October) of 2019, nitrogen and phosphorus contents and 8 heavy metals were monitored at 6 sampling points in the reservoir area, and the ecological risk assessment and traceability analysis were carried out by using the comprehensive pollution index method, the geo cumulative index method and the potential ecological risk index method. The results showed that the average values of TN and TP contents in the surface sediments of Qianwu Reservoir in wet and dry seasons were 2 010 and 433, 1 873 and 308 mg/kg, respectively. It presented the temporal and spatial distribution characteristics of high in the middle and low in the north and south ends. The comprehensive pollution index evaluation results showed that the overall TN of Qianwu Reservoir was heavily polluted, and TP was mildly polluted. The average contents of Hg, As, Cr, Mn, Ni, Cu, Zn, and Pb in the surface sediments of Qianwu Reservoir were 0.22, 10.64, 30.97, 293.25, 17.51, 21.01, 102.65, and 55.32 mg/kg, respectively. In terms of temporal and spatial distribution, except for Mn and Zn, the pollution of other heavy metals was heavier in wet seasons than in dry seasons. Affected by the topography of the reservoir and seasonal water transfer, except for Mn and Pb, the concentration levels of other heavy metals showed that the area from the head to the middle of the reservoir (points Q3 and Q4) during the wet season, and the area from the middle to the tail of the reservoir (Q2 and Q3) was high during the dry season. The evaluation results of the geoaccumulation index method and the potential ecological risk index method both showed that Hg was the main ecological risk contributing factor, with a contribution rate of 75.8%. The overall potential ecological risk level of the reservoir area was medium risk.