Compared with 20 years ago, the water quality of underground rivers has achieved fruitful results. To master the present situation of karst water quality in Guangxi, Guizhou, Yunnan, Chongqing, Guangdong and Hunan provinces. The results show that human activities have great influence on the quality of karst groundwater. It is pointed out that the water quality in karst areas cannot be managed and protected by accidental measurement data. We should further study the movement characteristics of karst water and the movement law of pollutants in southern China, find out the development law of underground rivers or karst springs, and protect important drinking water sources.
2. The influence of land use on karst groundwater
Karst spring is an important water source in karst areas in southern China. However, because the basin scope of karst spring is difficult to describe, the influence of land use on karst groundwater was mainly grasped from a macro perspective. According to land use and pollution sources, springs are divided into three categories. The ion concentration of different types of spring water is obviously different, which indicates that land use has obvious influence on groundwater quality. Some springs are obviously polluted, which is related to the fact that paddy fields, dry land and rural settlements are the main land use types in these places, that is, it is related to farming fertilization and domestic waste discharge. The chemical evolution of groundwater caused by agriculture and village construction in karst basin is discussed. Under the action of farmland non-point source pollution and domestic sewage in villages and towns, all links of water cycle are affected to varying degrees. Farmland and domestic sewage first affect shallow groundwater and surface water, and then transfer to deep underground river with water circulation. However, the vulnerability of karst springs in saturated zone is low and the hydrochemical changes are not obvious. It is also found that the influence of domestic sewage in villages and towns on the water quality of surface karst springs is more significant than that of farmland non-point source pollution.
3. Changes of main ion concentration and nitrogen budget in typical underground rivers.
The concentration of nitrate and sulfate is higher in rainy season than in dry season. The concentration of sodium ion, calcium ion, magnesium ion and bicarbonate ion decreased in rainy season; The change of potassium ion and chloride ion concentration is irregular, which is controlled by dilution, leaching or karst and human activities. Compared with the ion concentration in 1980s, the concentration of nitrate and sulfate increased obviously. The input and output of nitrogen in the underground river basin in one year are calculated with high accuracy, which provides a basis for the rational utilization of nitrogen fertilizer in karst areas.
4. Automatic monitoring of karst water system
According to the experience of automatic monitoring for many years, a set of construction methods of automatic monitoring project for karst water system are summarized. Based on the clear research purpose, it is proposed to draw the fragile distribution map of groundwater, understand the aquifer or water intake point strongly affected by human activities, and then arrange monitoring stations. The monitoring method combines automation and manual monitoring. Guide the construction of groundwater system monitoring project in karst area.