As a fragile factor of karst ecosystem

karst underground water system is highly sensitive to landuse change. Taking Houzhai subterranean stream basin

Puding County

Guizhou Province as an example. The im- pacts of intensity of agriculture activities

landuse change and irrigation system change upon underground water were analyzed based on more than 20 years' hydrochemical data. The results showed that both intensification of a- griculture activities

landuse change and irrigation system change can bring spatial and temporal change of under- ground water quality. Some are beneficial

such as co-irrigation of ground and underground reservoirs

vegetation planting(from farmland to forest); others are disbeneficial

such as urbanization

direct discharge of waste

and overuse of pesticide and fertilizer. Accordingly

underground water vulnerability should be considered during the landuse planning

thus help the harmonious development between human activities and resources and environ- ment.