表层岩溶系统水化学成因及植被恢复条件下变化趋势——以广西马山弄拉兰电堂泉为例

Cause and Change Trend of Water Chemistry of Epikarst System Under the Vegetation Restoration:A Case of Landiantang Epikarst Spring,Nongla,Mashan,Guangxi

常见的碳酸盐岩主要有灰岩和白云岩,两者的岩溶作用机理不同,因而常形成不同的地貌格局。在我国西南地区,若在小范围内有灰岩和白云岩出露时,往往在山体陡峭的部位出露质纯层厚的灰岩,而山间平原多出露白云岩。这种地层组合结构致使表层岩溶带的发育具有独特的双重岩性结构。基于兰电堂表层岩溶系统的研究,发现绝大部分水样的水化学类型均为HCO3-Ca·Mg型,其主要阳离子Ca2+和Mg2+质量浓度的季节动态变化趋势不明显,但对短期降水稀释效应及森林植被CO2效应的响应则非常迅速。将降水量小且比较均匀的8、9、10及12月水样的ρ(Ca2+)和ρ(Mg2+)关系曲线定义为"同比例溶解线",并用其判别不同降水条件下泉水化学成分差异的成因。另外,为了研究次生森林生态功能逐步恢复条件下岩溶作用强度的变化趋势,对近10年来弄拉表层岩溶泉水化学组分进行分析对比,发现岩溶水化学中主要阴、阳离子浓度均有增加趋势,也进一步佐证了森林植被的岩溶效应。

Limestone and dolomite are common carbonate rocks.Because of their different karstification mechanism,the different landscape would be formed.In Southwest of China,dolomitelocates on the different classes of karst basis level of erosion,while the pure limestone locates at upper the mountain.So,the epikarst zone has a duality structure because of the special strata combination.Based on the mornitoring to discharge and hydrochemistry of Landiantang epikarst spring,Nongla,Guangxi,it is found that the hydrochemical type of most water samples is HCO3-Ca·Mg.The variation trend of the Ca^2＋and Mg^2＋is not very clear in seasonal timescale.But it is more sensitive to short-term precipitation dilution and CO2 effect of forest vegetation.＂Equivaleng dissolution line＂（EDL）is defined by the relationship between concentration of Ca^2＋and Mg^2＋.In this paper,EDL can be used to distinguish the causes of the differences of spring hydrochemistry under different precipitation conditions.In addition,based on the analysis on nearly ten years data of the hydrochemistry and discharge data of Landiantang epikarst spring,it is shown that spring discharge and major ions concentration in karst water are all increased under the situation of vegetation restoration.All of above is further evidence of the vegetation effect in karst process.