| Water is the source of life, underground water is an important component of water resources, and there is a great amount of groundwater resources in karst areas. About 1/3 area of China is karst area, groundwater resources account for about 1/4 of total water resources, groundwater is an important water source, and is also the main drinking water source. Because of the dual hydrogeological spacial structure of karst water environment, forming the basic pattern:"land in the upstairs, water in the downstairs," because the soil is thin, often lack the natural impervious layer or filter layer, resulting in obviously fragile karst environment, the surface contaminants poured directly into the aquifer or underground river through karst sinkholes or other forms easily, then the groundwater polluted. In recent years, because of the rapid development of agriculture and industry, industrial waste water gradually increasing, the use of agricultural fertilizer, and pesticide is also increasing, so that our groundwater resources face serious challenges. Especially with the accelerated process of urbanization, cities were expanding, population was growing, rubbish and waste water generated in the process of urban living are constantly increasing, a large number of direct discharged wastewater and rainwater leachded the untreated waste heap field directly pour into rivers and then seeping into the ground, It is a serious threat to the quality of underground water resources and the health of people beside the downstream. Further investigation the source of pollutants, distribution, influencing factors and migration characteristics of subterranean stream downstream of City is helpful to reduce and control groundwater pollution, the maximum solve the problem of drinking water, to maintain people's lives stability and social stability in karst areas.This research focused on the Lihu subterranean stream in Nandan, researching the pollution of rubbish of urban life on the downstream. This study covers two aspects:First, studying the conventional ion distribution and variation in Lihu subterranean stream, Second, studying the distribution, Migration and transformation of ammonia in Lihu subterranean stream, in the meantime analyzing through the time and space, respectively. Research achieved:the influence of subterranean stream pollution in karst area is more severe than it is in Non-karst areas, for there is a lot of sinkholes, skylights, the entrance of subterranean stream in karst depressions, karst valley, the pollutants would pour directly into the subterranean stream, which resulting the deterioration of water quality in the subterranean stream, and the outlet of subterranean stream is usually the source of drinking water. The result shows the main pollution indicators in Lihu subterranean stream was ammonia. The concentration of ammonia had reached 26.5mg/L in Layi cave which is the entrance of Lihu subterranean stream. The concentration of NO2--N, Mn, TFe, COD and BOD in some samples had exceeded the State ClassⅢwater standards, and the concentration of As, Cr and N03--N had exceeded the State Class II water standards. The pollution in Xiaochang, Railway bridge, Brick bridge and Layi cave is the most serious, has basically can not use.In time, the changes of ammonia's concentration of Layi cave and Cool cave in Lihu subterranean stream is consistent, higher in February and march, in May and June to a minimum value, in July and later began to increase, in September reached the maxmun of the second half year, then decreased gradually, In contrast with the rainfall trend, the concentration of ammonia was lower in the flood period and higher in the dry season, effect of dilution in flood period and concentration in dry season played an important role. Effect of concentration in dry season also caused the concentration of K+, Na+, Ca2+, Mg2+, SO42-, PO43-, Cl- in Layi cave had a gradual upward trend in the period of October 2009 to April 2010 and August 2010 to December 2010, effect of dilution in the flood period caused the concentration of these ions at a low level in May, June and July. There were two abnormally high values of the concentration of NO3--N respectively in June and December, December is in the dry season, concentration of NO3--N was concentrated, June is in the flood period, fertilizers and pesticides used in the farmland along the Nandan river were brought into the river by rain.In space, nitrification was the main process of ammonia transport in Lihu subterranean stream, first, ammonia will transport into NO2—N, then NO2--N transport into NO3--N. Self-purification played an important role in improving water quality in subterranean stream.The trend of concentration of K+, Na+, Mg2+, Mn, Sr, Ba, Cl-, PO43-, F-December 2010 was consistent, similar variation with the conductivity, all of them had a lower level at the source, after into the town, the concentration of these ions in Lihu subterranean stream were constantly increasing with the increase of human activities, and had the highest value in Xiaochang, began to decrease downstream. Waste and waste water discharged by urban residents when living, especially the sewage discharged directly into Nandan river in Xiaochang were the main reason caused these indicators higher around Xiaochang. The concentration of SO42- was effected by area pollution, Acidic rain plus the use of fertilizer and pesticides in the farmland along the upstream had caused the concentration of SO42- at a higher level between source and Gantianba, almost all of the downstream is underground, lacking source and import tributaries lead the concentration of SO42-lowering after Gantianba, and nearly the lowest level when reached Xiaolongdong.The pollutant such as ammonia, Mn, TFe, BOD and COD mainly from Nandan country, waste and waste water from Nandan country disorderly row put in disorder is the major cause of Lihu subterranean stream pollution. |
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