岩溶作用对峰丛洼地土壤水中微量元素迁移的影响机制研究

Trace elements in soil are easy to accumulate in karst region, and the problem whether karstification promotes or inhibits the leaching of soil water trace elements is critical to learn the trace elements migration pattern, nutrition supply and environmental impact. This study will chose typical peak cluster depression of spatial heterogeneity as the research area and set karstification and soil water chemistry monitoring sites at the hilly-pass, slope, depression. .By monthly detecting the chemical indicators(such as pH, conductivity, main ion ), 3δCDIC and trace elements (Fe, Mn, Cu, zinc, and B) concentrations of soil water at different depths of soil, calculating the SIc and SId, and comparing with the monitoring data of soil CO2 and the dissolution rate in the soil, we will gain the spacial and seasonal change rule of karstification and trace elements concentration of soil water. .Base on those monitoring dates, we will also find out the migration pattern of trace elements from the top to bottom of soil profile and along the hill slope. Then we will analyze the correlation of karstification index with trace elements concentrations of soil water, to determine whether karstification in the soil influence the leaching of soil water trace elements..Moreover, we will sample and test karstification indicators and soil water trace elements concentration more frequently throughout the process of rainfall, to find out the influencing process and its mechanism of karstificaton on soil trace elements migration. The study is advantageous to acknowledge the characteristics of karstification under the soil, to enrich karst dynamics research method and content, to support the control engineering of rocky desertification and land utilization in karst region.

岩溶地区土壤微量元素易于富集，弄清岩溶作用对土壤水微量元素溶滤的作用机制和过程对掌握微量元素迁移规律、营养供给和环境影响十分关键。本项目选取空间异质性强的典型峰丛洼地为研究区，在垭口、坡地、洼地建立土壤水化学和岩溶作用监测点。每月采集不同深度土壤水样测定pH、电导率、主要离子等化学指标和13δCDIC、微量元素（Fe、Mn、Cu、Zn、B）浓度，计算SIc、SId和溶蚀量，结合土壤CO2浓度、溶蚀速率监测数据，获取岩溶作用指标和土壤水微量元素的空间差异和季节变化特征，剖析微量元素在土壤剖面和坡面的迁移规律及与岩溶作用指标的相关性。对降雨事件影响下的土壤水进行全过程加密取样，监测岩溶作用指标和土壤水微量元素浓度变化，揭示岩溶作用对土壤微量元素迁移的影响过程和机制。研究将丰富岩溶动力学研究方法和内容，有助于掌握土壤中岩溶作用特征和元素迁移规律，为峰丛洼地石漠化治理、土地利用和土壤改良提供支撑。

针对岩溶地区土壤微量元素易于富集，岩溶作用对土壤水微量元素溶滤的作用机制和过程不清的前沿科学问题，选取空间异质性强的典型峰丛洼地广西桂林丫吉试验场和寨底基地为研究区，研究岩溶地区土壤富集微量元素的原因和机制，阐明了岩溶作用的影响。（1）从峰丛洼地的上部到下部，即垭口→中坡→坡麓→泉，土壤水Ca2+、HCO3-浓度持续增大，而Fe、Mn、Cu、Zn、B微量元素浓度先增大后减小，至坡麓出现陡降；溶蚀速率垭口（11.91 mg/a*cm2）˃中坡（8.26 mg/a*cm2）˃坡麓（3.04 mg/a*cm2）；表明，垭口→中坡（岩溶作用前阶段），土下溶蚀作用能促进溶滤作用，离子浓度普遍增大，中坡→坡麓（岩溶作用后阶段），土下溶蚀作用和溶滤作用都减弱，但溶蚀作用持续进行形成的高Ca2+和HCO3-环境，阻碍了微量元素向土壤水迁移，及形成限制微量元素迁移的钙质屏障。（2）深层土壤水Ca2+和HCO3-较浅层高，而微量元素反之，深层溶蚀速率亦较显著小于浅层，因此深层土壤水环境亦表现为较浅层强的钙质屏障作用。（3）8个监测点的水化学相关性分析显示，pH和Zn、Mn、B，Ca2+和Fe、Al、Pb、Zn、Mn、Cu，HCO3-与Fe、Al、Pb、Zn、Mn、B，呈负相关关系。 研究结果表明，随着溶蚀作用的持续进行，溶蚀作用后阶段土壤水、岩溶水钙质屏障作用亦逐渐增强，在此过程中Ca2+和HCO3-大量淋溶输出，在岩土界面及以下表层岩溶带形成降低微量元素活性的水化学环境，阻碍其迁移，使微量元素在地形低洼和变缓处的土壤中累积、富集。钙质屏障作用（带）具有高pH和Ca2+、HCO3-特征，且分布不均匀，会受岩性、地貌、土层厚度、植被条件、降雨等因素的影响。研究能有助于掌握峰丛洼地区微量元素总体空间分布特征和营养供给特点，为峰丛洼地土地利用和土壤改良提供依据。