岩溶地下河污染物运移特征及自净能力——以广西里湖地下河为例

Contaminant transport behavior in a karst subterranean river and its capacity of self-purification: A case study of Lihu,Guangxi

以广西里湖地下河为研究对象,通过观测地下河系统中污染物的运移行为来研究其自净过程。于不同季节沿着地下河的径流方向进行一个水文年的调查取样。结果发现地下河主要受到NO2-N、NH+4-N、COD和As、Cd、Hg等重金属的污染。污染物从地表进入岩溶含水层,到达地下河出口时部分污染物浓度衰减明显,说明一些离子有明显的自净能力。因地下河的结构和部分管道半充水状态、明暗流交替等水文地质条件,地下河的自净机制主要是物理过程的稀释作用和化学过程的氧化还原反应。通过对比地下河主要离子的衰减量和衰减速率,发现衰减比例最高的为铵态氮,最低为保守元素氯离子。根据衰减速率,将水中的离子和微量元素分为4种衰减特征类型:TFe、Al和Zn一旦进入岩溶含水层后全部衰减;K、Na、Mg、F、Cl、HPO4和TP在洞穴伏流段具有最高的衰减速率;来自生活和工业污染的NH4-N、CODCr、BOD5从上游至下游逐渐减少;Mn、Ba和Hg从明流转为伏流时衰减速率最快,但在洞穴伏流内存在二次悬浮。

Lihu subterranean river in South China was selected to study the contaminant transport behavior and self-purification capacity of a karst aquifer. The subterranean river was investigated through water sampling along the stream reach for one year. Analysis of inorganic ions and trace elements in different seasons and at different locations showed the major contaminants are NO2--N, NH4＋-N, COD, As, Cd, and Hg, due to domestic waste, mining industrial waste, and fertilizer application in the recharge area. Along the course of the karst conduit, a self-purification process was observed because of significant decrease in some ions concentration. The mechanism of self-purification was caused by dilution and nitrification, which was determined by the suterranean river＇s structure and hydrogeological condition. By comparing the attenuation quantity and percentage of ions, it was found that ammonium had the highest, while chloridion had the lowest percentage. According to the attenuation rate, four types of attenuation character could be classified. Firstly, the ions decayed completely after they entered the karst aquifer, such as TFe, Zn, and Al; secondly, the ions had the highest attenuation rate when they traveled underground through the aquifer, such as K, Na, Mg, F, Cl, HPO4, and TP; thirdly, the concentration gradually decreased from upstream to downstream, which was represented by NH4＋-N, CODCr, and BOD5; and finally, they had the highest attenuation rate when transformed from surface stream to underground stream, but secondary suspension of contaminants could happen in the cave, such as Mn, Ba, and Hg.