喀斯特石漠化过程中植被演替及其对径流水化学的影响

通过对贵州中部喀斯特地区进行植被调查以及土壤和径流样品的分析，探讨石漠化过程中植被演替及其对径流水化学组成的影响。结果表明：喀斯特石漠化后，土壤出现粘质化，有机质含量急剧下降，土壤毛管孔隙度下降，干旱季节表层和次表层土壤的含水量明显减少，改变了生态系统的水分运动规律。喀斯特地表径流中离子浓度的大小排序为HCO3^-＞SO4^2-＞Ca2^2＋＞Mg^2＋＞K^＋、NO3^-、Cl^-＞Na^＋＞NH4^＋＞PO4^3-，地表径流水化学类型以HCO3-Ca型为主；随着石漠化程度的增加，地表径流中PO4^3-输出量明显增加，其次是Ca^2＋、NO3^-，这部分养分的流失造成土壤养分水平下降，同时影响受纳水体的环境质量。地下径流离子组成与地表径流总体相似，但HCO3^-、Ca^2＋、Mg^2＋的含量高于地表径流，而K^＋、NH4^＋的含量低于地表径流；石漠化发生后，地下径流中HCO3^-、Mg^2＋浓度明显减少，岩溶作用减弱，而NH4^＋、NO3^-浓度明显增加，对地下水质产生一定的影响。

VEGETATION SUCCESSION WITH KARST ROCKY DESERTIFICATION AND ITS IMPACT ON WATER CHEMISTRY OF RUNOFF

Karst rocky desertification is a land degradation process,involving serious soil erosion,extensive exposure of(basement) rocks,drastic decrease in soil productivity,(and) appearance of a desert-like landscape.As it is a serious (problem) in(Guizhou) Province,studies were carried out on succession of the vegetations on lands under karst rocky desertification and its(impact) on chemical composition of runoffs from the lands in this region through vegetation surveys(and) analysis of soil and runoff samples.The(results) show that with development of (karst) rocky(desertification,) the soil was losing organic matter rapidly,(becoming) clayey in texture,decreasing in soil(capillary) porosity and in water-holding capacity in(the) surface or subsurface soil(layers) significantly during dry seasons,thus altering the law of water movement in karst ecological system.The analysis of (chemical) composition of surface(runoffs) show that in terms of concentration,anions and cations in the surface runoffs were in the order of HCO~-_3>SO~(2-)_4>Ca~(2 )>Mg~(2 )>K~ ,NO~-_3,Cl~->Na~ >NH~ _4>PO~(3-)_4.With karst rocky(desertification) going on,the output of PO~(3-)_4in the surface runoff increased(significantly,) and that of Ca~(2 ) and NO~-_3 followed,(thus) leading to(decrease) in soil fertility and affecting (environmental) quality of the recipient waterbodies.The variation of chemical(composition) of ground(runoff) was similar to that of the surface runoff,but the concentrations of(HCO~-_3,) Ca~(2 ),and Mg~(2 ) were higher than that in the (surface) runoff,respectively,while the concentrations of NH~ _4 and K~ lower than that in the surface runoff.The(concentrations) of HCO~-_3 and Mg~(2 ) were reduced(obviously) with karst rocky desertification proceeding on,thus (weakening)(karstification,) while the concentrations of NH~ _4 and NO~-_3 were increased significantly,thus affecting the quality of(ground-water,) to some extent.