太湖流域污水排放对湖水天然水化学的影响

为揭示太湖流域污水排放对湖水天然水化学(主要离子)的影响,对太湖上游19个污水处理厂的进水、出水及雨水、入湖河水和湖水中主要离子进行了分析,同时收集历史数据对比了太湖1950s年代和目前的天然水化学特征.结果表明,太湖水体天然水化学类型主要受流域碳酸盐岩风化作用控制,而受雨水影响较小;流域排放的污水主要离子特征类似于干旱地区的河水,部分工业污水甚至具有海水水化学特征,说明人为活动对当地淡水水质的重要影响.同时,太湖水化学已从60年前的重碳酸盐钙型水转变为目前的氯化物钠型水.进一步通过修正的完全混合断面污染物浓度模型的计算结果显示,生活污水排放可以解释对太湖多数主要离子的影响,生活和工业污水的排放可以更好地解释Cl#的变化;但太湖Ca2+和Mg2+浓度(硬度)的增长受污水影响较小,而是受流域酸沉降的影响控制.分析显示,60年来受流域不断增长的污水排放影响,太湖水体的优势阴阳离子组分均已发生了显著变化,目前湖水(Ca2++Mg2+)-HCO-3和(Na++K+)-Cl-均分布在1∶1线上侧,而(Ca2++Mg2+)/(Na++K+)比值则下降了约1半,同时湖水的Cl#/Na+比值显示出显著的升高趋势,说明流域人类活动已经成为影响太湖水化学的主要原因.本研究可为湖泊水化学演化研究及强烈人为干预条件下的水环境管理提供新的基础.

Impact of sewage discharge on the water chemistry of Lake Taihu

To explore the impact of sewage discharge on the water chemistry (major ions) of Lake Taihu, major ions in the lake water, rainwater, river water from local area and wastewater from 19 sewage treatment plants located in the upstream of Lake Taihu were analyzed. Historical water chemistry data were collected to compare with current measured results. The results indicated that the natural lake water chemistry of Taihu was controlled by carbonate weathering in the basin while the impact of rainwater was negligible. The water chemistry of the effluent in the basin was similar to the river water in arid regions, and some industrial wastewater was even close to the seawater in terms of the water chemistry characteristics, which suggests that human activities have a significant impact on the local freshwater water quality. Consequently, the natural water chemistry of Taihu lake has changed from the calcium carbonate to the present sodium chloride during the past six decades. Furthermore, our calculation with the corrected mixing model indicated that sewage discharge well explained the change of many major ions in the lake water; while the domestic and industrial wastewater discharges together well explained the Cl^- change in the lake. However, sewage discharges had little effect on the increased concentration of Ca²⁺and Mg²⁺ (Total Hardness), which instead was affected by local acid deposition. This study suggested that the dominant major ions in the lake water changed significantly compared with that of 1950s because of the ever-increasing sewage discharges. Calculation results showed that current (Ca²⁺+Mg²⁺)-HCO₃^- and (Na⁺+K⁺)-Cl^- values were above the 1:1 line; the current ratio of (Ca²⁺+Mg²⁺)/(Na⁺+K⁺) decreased by 1-fold compared with that of 1950s; and the ratio of Cl^-/Na⁺ increased significantly in the past six decades. This indicate that current water chemistry of Lake Taihu is dominated by human activities instead of natural weathering. This study provides a new basis for the research of lake evolution and for the water environment management under the circumstance of intensive human interventions.