喀斯特坡地土壤-表层岩溶带养分流失的水文驱动机制

Karst landforms are the product of dissolution by natural water of surface and subsurface carbonate rock, showing a complex three-dimensional integrated natural system comprised of rock, water, soil, vegetation and atmosphere elements. A network of solution-enlarged joints and cracks results in excessive surface water loss to the underground through deep percolation and seepage. Recent studies found that human disturbance caused rapid nutrients loss in karst environment, which further deteriorated the inherent fragile karstic ecological system. Runoff and soil erosion are the main causes of nutrients loss in non-karst areas. Whether there are some links between rapid surface water loss and rapid nutrients loss in the karst environment, if there are such links, then to what extent, and how do they work? These questions remain to be answered in order to develope effective nutrients loss controling methods as well as to further promote rocky desertification combating projects in southwest China. The aim of this project therefore is to answer these questions from the point of view of considering the vegetation-soil-epikarst system as an integrated whole. Firstly, a three-dimensional structure investigation will be carried out on the karst hillslope experimental plots (each of 100 m2) equipped for three dimensional processes monitoring for both soil and water, to reveal intercoupling features between soil and epikarst within the near-surface karst system from both qualitative and quantitative perspectives. Secondly, various methods, such as in situ rainfall simulation, chemical and hydrogen/oxygen isotope tracers tests, and hydrochemical monitoring under natural weather condition, will be respectively adopted, to evaluate the effects of soil-epikarst's inner structure factors, external environmental factors, and land use patterns on the three dimensional coupling behaviors of runoff generation and nutrients loss. Based on the above experiments, we attempt to reveal how hydrological factors, including flow pathways, runoff generation mechanisms, water residence time, threshold rainfall, affect karstic ecosystem's rapid nutrients loss, and to develop karstic three dimensional nutrients loss models based on soil-epikarst sturcture factors and water balance equations. The results of this project will provide scientific basis for maintaining and promoting the ecosystem service functions in the karst region of southwest China.

喀斯特二元结构发育，地表水大量漏失，在人类干扰下，原本脆弱的生态系统表现出养分快速流失的特点，然而快速流失的养分是否同样以地下流失为主，受何种产流机制驱动等问题还不清楚，这影响了养分流失阻控技术的提出和石漠化治理工程的深入开展。本项目针对以上问题，依托喀斯特坡地三维水土过程研究平台，将植被-土壤-表层岩溶带作为一个整体考虑，通过三维结构调查，明确土壤-表层岩溶带的相互耦合关系及其结构因子的定量描述方法，结合原位模拟降雨、离子和氢氧同位素示踪、自然降雨监测等技术，对土壤-表层岩溶带结构因子、外部环境因子、土地利用方式影响下的喀斯特坡地三维产流和养分流失过程进行耦合研究，从水文路径、产流机制、水分滞留时间、降雨产流阈值等角度揭示土壤-表层岩溶带养分流失的水文驱动机制，建立基于土壤-表层岩溶带结构和水量平衡方程的喀斯特养分流失模型，为区域生态服务功能的维持和提升提供科学依据。

喀斯特二元结构发育，地表水大量漏失，在人类干扰下，原本脆弱的生态系统表现出养分快速流失的特点，然而快速流失的养分是否同样以地下流失为主，受何种产流机制驱动等问题还不清楚，这影响了养分流失阻控技术的提出和石漠化治理工程的深入开展。本项目针对以上问题，依托喀斯特坡地三维水土过程研究平台，通过模拟降雨结合自然降雨监测的方法，将喀斯特坡地三维多界面产流过程与养分流失过程进行了耦合研究，在喀斯特地表-地下三维水土过程监测方法、界面产流及养分丢失过程机理、水土资源高效利用技术研发等方面获得了系列成果。1）土壤-表层岩溶带结构因子定量及其水土过程监测方法方面：通过物探及钻探等手段，实现了喀斯特坡地（0-10m范围内）岩土结构的探测与定量，发明了适宜该区水土过程模拟监测的系列方法，解决了传统水文-侵蚀过程观测研究方法在喀斯特区不适用的问题。2）产流机制方面：基于山坡试验水文的方法，系统刻画了喀斯特土-气界面与土-岩界面产流的触发机制（壤中流填充-溢出、地表径流超渗-蓄满），明确了喀斯特坡地土壤物质迁移的水文驱动机制，深化了喀斯特近地表产流与土壤侵蚀理论。3）氮素三维流失途径方面：发现硝态氮浓度在深层渗漏中最高，铵态氮浓度在岩土界面壤中流中最高，深层渗漏对氮素流失的贡献率达89%，显著高于地表径流和壤中流；旧水是喀斯特坡地携带氮素迁移的主要介质。4）基于以上研究，研发出喀斯特坡地土岩界面产流水集蓄利用技术，列入“水利部水利先进实用技术重点推广指导目录”；基于地表-地下水土流失/漏失机理认识，创建了峰丛坡地水-土-养分漏失阻控与循环高效利用模式。项目实施过程中，共发表SCI收录4篇，CSCD收录4篇，授权国家发明专利2项，申请国家发明专利2项，获批水利部节水技术行业标准1项，获广西科技进步一等奖1项，培养研究生6名。取得的科研成果有望在喀斯特区水土资源合理利用、洪涝预警、面源污染防控等方面提供重要理论支撑。