CHEMICAL EVOLUTION OF GROUNDWATERS UNDER THE IMPACT OF AGRICULTURAL ACTIVITIES AND SETTLEMENT IN KARST BASIN
GUO Fang, JIANG Guang-hui(Institute of Karst Geology , CAGS, Karst Dynamics Laboratory, MLR, Guilin, 541004, China)
A karst basin was one of the geological cells where water, soil resources are rich and anthropologic activities have heavy impact on the environment. Water circulation in the karst basin often has a single outlet, and it begins with precipitation, then is regulated by epikarst zone, river network, aeration zone and saturated zone, finally reaches to the karst conduit. Water quality is affected by non-point sources from agriculture and settlement. Forty samples were taken from epikarst springs, saturated zone springs, sinkholess and outlet of the karst conduit. The result indicated that : (1) The concentrations of K+, Na+, Ca2+, Mg2+, Cl-, SO42-, HCO3-and NO3-in epikarst springs increased a little, and dispersion of K+, Na+ and Cl-concentrations increased, too. (2)K+, Na+ and Cl-in shallow groundwater (represented by epikarst springs), surface water (represented by sinkholes) and karst conduit were very similar, but much distinguished from saturated zone springs. (3) SO42-in shallow groundwater and surface water was similar, but different from saturated springs and karst conduits. (4) NO3-in epikarst springs was highest than others. It could be concluded that: (1)agricultural non-point source pollution and domestic waste firstly polluted shallow groundwater and surface water, and then polluted karst conduit water. While saturated springs had stronger capability of self-protection, representing no obvious change in water quality. (2) impact of domestic waste on epikarst springs was more serious than agricultural non-point source pollution.