粤西三座重要供水水库沉积物营养盐负荷与重金属污染特征

摘要

为揭示粤西3座供水水库（高州水库、鹤地水库、大水桥水库）沉积物营养盐负荷及重金属污染特征，于2008年6月在各水库大坝前湖泊区采集柱状沉积物，运用SMT法、碱性过硫酸钾消解法、烧失法和ICP-MS法分别测定其柱状沉积物中氮磷营养盐、有机质和7种重金属（Cu、Pb、Zn、Cd、Ni、Cr与Hg）的含量，并采用潜在生态风险指数法对表层重金属污染的潜在生态风险进行评价，同时通过相关性分析重金属的可能来源。结果表明：3座水库沉积物总氮质量分数为1.13~3.37 mg·g-1，有机质为11.83~20.37 mg·g-1，其表层总氮、有机质的质量分数大小顺序为高州水库>大水桥水库>鹤地水库，总磷的质量浓度在0.22~0.77 mg·g-1之间，其表层总磷质量分数大小顺序为高州水库>鹤地水库>大水桥水库，在垂直剖面上，总氮、总磷与有机质的质量分数在16 cm至表层沉积物垂直断面显著高于其他断面，表明近些年来水库内源营养盐负荷逐渐加重。重金属质量分数平均值均高于广东省土壤环境背景值，总体呈现随深度增加而降低的趋势，但3座水库间重金属质量分数差异较大，其中鹤地和高州水库的Zn和Pb污染相对严重（质量分数分别为Zn：353.15、693.35 mg·kg-1；Pb：74.51、127.91 mg·kg-1），大水桥水库的Cr和Ni污染相对严重（质量分数分别为Cr：238.69 mg·kg-1；Ni：251.06 mg·kg-1）。潜在生态风险评价表明，3座水库Cd和Hg具有高的生态危害，应引起重视，其他重金属则处于轻微的生态危害等级。同时沉积物高有机质的质量浓度经矿化分解可能加剧水体重金属生态危害。根据相关性分析和其他相关资料可知，粤西农业区大量化肥农药面源污染汇入造成水库初级生产力提高并最终沉降可能是沉积物营养盐、有机质与重金属的主要来源。%Sediment cores were sampled from the three reservoirs of west area of Guangdong province in June, 2008. Total nitrogen (TN), total phosphorus (TP), organic matter (OM) and the main heavy metals including Cu, Pb, Zn, Cd, Ni, Cr and Hg in sedimentcolumns were determined by SMT, Alkaline Persulfate Digestion, loss on ignition Method, ICP-MS, respectively. Pollution of heavy meteals was evaluated by potential ecological risk index, and the possible sources of heavy metals were estimated with correlation analysis. The results showed that contents of total nitrogen TN and OM ranged from 1.13-3.37, 11.83-20.37 mg·g-1, respectively. TP ranged from 0.22-0.77 mg·g-1, the total nitrogen (TN) and the organic matter (OM) content in the surface sediments followed the order: Gaozhou Reservoir > Dashuiqiao Reservoir > Hedi Reservoir, whereas, total phosphorus (TP) is: Gaozhou Reservoir > Hedi Reservoir > Dashuiqiao Reservoir. From the depth of 16 cm to the surface in sediment columns, TN, TP and OM were significantly higher than others, and implied that internal loading getting heavier in recent years. The content of heavy metals was higher than the background values of soils in Guangdong province, and decreased with increasing depth, but there were great variations among the reservoirs. Zn and Pb polluted seriously in Hedi Reservoir and Gaozhou Reservoir (Zn: 353.15, 693.35 mg·kg-1; Pb: 74.51, 127.91 mg·kg-1), where as Cr and Ni showed serious pollution in Dashuiqiao Reservoir (Cr: 238.69 mg·kg-1; Ni: 251.06 mg·kg-1). We introduced risk index (RI) to evaluate the potential ecological risk of heavy metals, and results showed that there was low ecological risk except for Cd and Hg in the three reservoirs. However, mineralization of OM would result in heavy metals release into waterbody and increase ecological risk of heavy metals. Based on the correlation analysis, over input of fertilizer and pesticide would be the main source for the primary productivity and heavy metals, and settling to sediment in west area of Guangdong province.