Impact of human activities on the groundwater environment in the Mengzi basin, Yunnan Province

The Mengzi basin, located in southeastern Yunnan Province, is an irregular lacustrine plain with an area of 544.2 km2. The basin elevation is from 1,281 to 1,350 m, and the cover is generally 100 to 300m thick. The bottom of the basin is carbonate strata. It is the primary area of cultivated land distribution, population concentration and economic activity in Mengzi City. In recent years, the rapid development of social economy has brought about a series of problems, such as the decline of groundwater level and pollution of groundwater.This paper is based on the 1∶50,000 hydrogeological survey project of China Geological Survey. Through field investigations, sampling, pumping tests and dynamic monitoring, the influence of human activities on the groundwater environment in the Mengzi basin is studied, which is evidenced by the characteristics of groundwater environment change in the past 30 years. Compared with the previous research, in the last 30 years 20 natural springs in Quaternary cutoff in the basin. Groundwater level overall declined 5-20 m. The salinity and hardness of groundwater increased, particularly the content of Cl- and SO42-, and groundwater types became from the original two to ten. The water quality of ground water deteriorated, and the percentage of the total number of samples with good water quality and above reduced from the original 80% to 17.4% at present. The urban expansion, economic development and population expansion of the Mengzi area lead to the increase of the demand for groundwater resources, resulting in cut of spring water and decline of groundwater level. The discharge of waste water and the increase of chemical fertilizer in industrial and mining enterprises lead to the increase of salinity and hardness of groundwater, and the diversity of groundwater types. Industrial waste water and domestic sewage are discharged in a random way, and a large amount of pesticides and fertilizers are used, which leads to pollution of the surface and ground water.It is strongly suggested to control the exploitation of groundwater strictly, strengthen the monitoring and management, and rationally develop and effectively protect the groundwater resources in study area.