水文地质条件对岩溶地下暗河污染的影响

Influence of hydrogeological conditions on the pollution of karst underground rivers

通过收集基础资料、岩溶水文地质调查、水体污染指标分析等多种手段,分析了水文地质条件对贵州西南部某岩溶暗河地下水污染的影响。认为:(1)暗河出口所包含的六处泉点、两处溶洞,平面分布位置集中,但其水质污染情况各异,表明其分属于不同的地下岩溶水系统,暗河岩溶地下水系统极为复杂。岩溶暗河出口在空间平面上呈多股、条带状泉眼展布出露,主要受地质相变带附近构造及岩体本身异质性控制。(2)调查区受新构造运动的强烈抬升和河流快速下切的影响,形成了发达的地下岩溶水系统和岩溶洞穴系统,存在多股明流与伏流组成的水文地质单元体,客观上为暗河污染创造了条件。(3)暗河污染物来源为秧家坝岩溶洼地内某养猪场养殖废水,且是集中式、间断性通过落水洞进入地下岩溶管道。建议该岩溶暗河补给区应当控制发展大型养殖业及大中型集镇建设,污废水应当加强回收利用和减少外排,加强区内水源地建设与保护工作。

With an area of about 5×105 km^(2),the largest contiguous karst area in the world is distributed in Southwest China.Karst underground rivers are the most important karst landscapes in karst areas,and also important water sources for human production and life in karst areas of Southwest China.However,with the development of industry and agriculture,the intensification of human activities,and the openness and vulnerability of the karst aquifer system,karst groundwater is facing many threats such as water pollution,depletion of water resources and so on.The water body of a karst underground river in southwestern Guizhou Province was seriously polluted,which resulted in the pollution of the water body of Qingping river downstream.Muer cave,one section of the Qingping river,is a first-class protection area of drinking water source.There are about 30,000 people living in the surrounding towns,in which water for drinking and irrigation is taken from the Muerdong underground river;therefore,the pollution of this river will greatly influence the people's life.This paper studies the influence of hydrogeological conditions of pollution in the karst underground river by means of basic data collection,analysis of karst hydrogeological conditions,microbial indicators and water pollution indexes.The results show as follows:(1)Muer cave is located near the phase transition zone between karst and non-karst rocks,with highly permeable carbonate rocks in the west and weakly permeable clastic rocks in the east.Groundwater in this area is discharged to the surface in the form of karst underground river in Muer cave near the lowest discharge datum.(2)Because of the strong uplift of neotectonic movement and the rapid cut-off of rivers,the underground karst water system and karst cave system have been developed in this area,and there exist multiple complex hydrogeological units formed by surface flows and underground flows,which may create conditions for the pollution of underground river caused by surface pollutants penetrating into underground karst water system.(3)Six spring points and two karst caves are concentrated at the outlet of the Muerdong underground river,but their water quality is different,which indicates that they belong to different underground karst water systems.This also indicates that the range of recharge source of Muerdong underground river is wide,the regional karst groundwater system is very complex,and the ecological environment of the underground river is vulnerable.(4)The characteristics that pollutants are discharged in a concentrated way and in a large amount indicate that the discharge channel is relatively unblocked after the infiltration of pollutants into the underground.It is likely that pollutants are discharged through channels with large cross-sections such as karst pipelines developed in the soluble rock,instead of small channels like bedrock fractures in non-soluble rocks.Therefore,sources of pollution may be distributed in the area west of the Muludong river.Few households are scattered in the upper reaches of the Muerdong underground river,and the sewage such as residents'excreta is mainly stored in septic tanks and used for irrigation.Besides,given that no large industrial and mining enterprises or schools,etc.have been established,there exist no conditions that sewage such as human excrement is discharged in a concentrated way and in a large amount.Therefore,we can exclude the possible pollution caused by the discharge of human excrement and other sewage into the underground river.According to the field investigation,water quality monitoring and microbial index analysis,the pollutants may be the excrement of livestock.By tracer connectivity test and investigation of the surface,we can exclude the pollution sources from the areas of Dajiang(Ronglai)trough and Tanping trough.The Yangjiaba karst depression is characterized by high elevation and thick water-rich rock mass.Under the control of topographic height difference and fault structure,groundwater flows from west to east along the karst cave and karst pipeline system to the outlet of the Muerdong underground river.The geophysical prospecting results also show that there is a deep karst pipeline system in the lower part of Yangjiaba karst depression.At the same time,combined with microbial indicators of water samples from this depression and from Muerdong spring,the source of discharge of livestock was from a piggery in Yangjiaba karst depression.Several sinkholes located in this piggery become the channels of discharging sewage and pig excrement which are likely the source of pollutants in the Muerdong underground river.In this study,some suggestions have been put forward.In the economically underdeveloped karst areas,the protection and treatment of karst spring water is relatively difficult under the background of economic and social development.In accordance with the principles of controlling,recycling,and reducing pollutant discharge,strengthening the protection of water sources and improving the environment,the development of large-scale aquaculture and the construction of large and medium-sized towns in the recharge area of the Muludong underground river should be controlled,sewage of livestock and domestic sewage should be recycled to reduce the discharge of pollutants.At the same time,it is suggested to strengthen the local construction and protection of water sources and increase new stable and reliable drinking water sources.