极端暴雨条件下广东北江重金属污染特征

Characteristics of Heavy Metal Pollution in Beijiang River during Extreme Storm Runoff Event

以2012年"6.25"暴雨径流过程为对象,研究广东省北江上游高桥断面在极端暴雨条件下水体理化性质与ρ(Pb)、ρ(Cu)、ρ(Zn)、ρ(Cd)(均为溶解态,下同)的变化过程;基于相关分析法,分析北江水质对水文过程的响应关系及各指标间的内联特点.结果表明:暴雨径流期间,北江水质呈"大流量、高浓度"的特征.暴雨径流发生前后4个典型阶段中,阶段Ⅰ(局部产流期)ρ(Cd)、ρ(Pb)仅为(0.48±0.09)和(1.91±0.29)μg/L,ρ(Cu)与ρ(Zn)基本未检出;阶段Ⅱ(以地表径流为主的全流域产流期)ρ(Cd)、ρ(Pb)、ρ(Cu)与ρ(Zn)均迅速上升,最高分别达1.80、12.34、6.18、52.57μg/L;阶段Ⅲ(以浅层地下水径流为主的全流域产流期)重金属质量浓度整体较洪水期有所下降,但ρ(Pb)仍高于阶段Ⅰ正常水平,ρ(Zn)、ρ(Cu)和ρ(Cd)则低于阶段Ⅰ;阶段Ⅳ(深层地下水产流期)ρ(Cu)与ρ(Zn)已回落至未检出水平,ρ(Cd)持续下降,低于阶段Ⅲ和阶段Ⅰ,ρ(Pb)较阶段Ⅲ有所下降,但仍高于阶段Ⅰ.暴雨径流期间,溶解态重金属质量浓度与流量及浊度间呈显著正相关(P<0.01),ρ(Zn)与ρ(Pb)、ρ(Cd)的相关系数均在0.85以上(P<0.01).

The physio-chemical characteristics and dissolved metal （copper, lead, zinc and cadmium） concentrations from samples from Gaoqiao segment of upper Beijiang River during a storm runoff event on June 25^th , 2012, were analyzed. By Pearson correlation analysis, inter-correlative characteristics among hydrodynamics and metal concentrations were also investigated. The results revealed that during the storm runoff period, species concentrations showed similar patterns as river flow, and could be illustrated as ＂higher flow, higher metal concentrations. ＂ Cadmium and lead concentrations were merely at （0.48 ± 0.09 ） and （ 1.91 ± 0.29 ） Irg/L in the first stage, known as a partial flow generation period, while copper and zinc were barely detected. At the second stage, when river discharge was composed primarily by surface flow from the entire watershed, cadmium, lead, copper and zinc concentrations grew rapidly up to max level of 1.80, 12.34, 6. 18 and 52.57 μg/L, respectively. At the third stage, when flood began to recede and river flow was mainly affected by shallow groundwater, copper, zinc and cadmium concentrations dropped somewhat, but lead level was still above the normal level, while zinc, copper and cadmium concentrations were below the normal level. In the fourth stage, when river flow was mainly from deeper groundwater, copper and zinc concentrations dropped below the detection level, while cadmium level continued to fall, lower than the third stage but still higher than the normal level despite continuous dropping. Correlative analysis showed that dissolved metal concentrations （ lead, zinc, copper and cadmium ） were significantly correlated with turbidity and river flow （ P 〈 0. 01 ）. The same pattern was also found among zinc：, copper and cadmium species concentrations, where Pearson coefficients were above 0. 85 （P 〈0. 01）.