The Change Of Karst Vegetation System And Its Impact On Soil-water Quality And Environmental Evalution

This text focus on the changes of soil quality by vegetation degradation in the middle part of Guizhou karst area and its impact on the water quality of runoff and groundwater in this region by the way of analyzing typical soil and water samples. The results show the following main conclusion:1. Along with the karst degradation of vegetatable communities , the content of soil organic matter, available N, P, K and the soil capillary porosity decreased. The water -holding capacity in surface and subsurface soil reduced during dry seasons significantly.2. The result also showed the types of soil quality in the progress of karst vegetation degradating divided three groups: (1)the soils wherein the content of organic matter , available N, P, K were > 100 g/kg, >350 mg/kg, >10 rag/kg, >120 mg/kg, ; (2) the soils wherein the content of organic matter , available N, P, K were > 50-100 g/kg, 200-350 mg/kg, 5-10 mg/kg, 80-120 mg/kg; (3) the soils wherein the content of organic matter , available N, P, K were < 50 g/kg, < 200 mg/kg, < 5 mg/kg, < 80 mg/kg.3. With the vegetation degradating , the loss of NO₃^-\ NH₄⁺\ PO₄^3- in runoff of karst hillside fields increased. In condition of crop planting, the loss of NO₃^-\ NH₄⁺ PO₄^3- , K⁺ influenced by the plant rules and fertilizer quautity, which was positive correlation to the contents of soil available N, P, K.4. The composition of water in surface runoff under various vegetations, is HCO₃^- > Ca²⁺ > SO₄^2- > Mg²⁺ > NO₃^- > Cl^- > Na⁺> K⁺> NH₄⁺ > PO₄^3- . During the vegetation degradating, the concentrations of HCO₃^- Ca²⁺ Mg²⁺ are obviously reduced while the SO₄^2- NH₄⁺ PO₄^3- concentration increased in the runoff, which makes the karst water quality aggravate.5. Karst groundwater quality in different plants-soil system are tentatively divided three groups. In group I , the quality of groundwater from forest land reaches national standard I - II qroundwater quality; In groupll.the quality of groundwater from bush forest land and shrub forest meadow are within the range of I-III—; In groupIII, the quality of groundwater from farmland reaches II- IV— water quality.