砾石对华北土石山区坡面水分运移的影响

Rock fragments (≥2mm in diameter) are widespread in mountain soils, and play a critical role in soil hydrological process. However，the quantitative relationship between rock fragments and soil hydrological processes remains unclear because of the strong heterogeneity of spatial distribution of rock fragments. A method that combines field experiment (e.g., dyeing tracer) and soil column simulation (e.g., CT scanning and solute transport) will be used in this study. Rock fragments structures such as coverage, content, size and position in different slope aspects, positions and soil depths will be investigated in order to confirm the spatial distribution of rock fragments on hillslopes. On this basis, we will measure and analyze soil hydrological parameters (e.g., soil bulk density, mechanical composition and hydraulic conductivity), soil macropore characteristics (e.g., amount, diameter and porisity) and soil water movement (e.g., surface runoff, infiltration, soil moisture and preferential flow) in different slope aspects and positions. Finally, effects of rock fragments structures on soil hydrological parameters and macropores will be identified; a quantitative relationship between rock fragments structure and soil water movement will be established; and the effects of rock fragments on slope water movement will be illustrated. These findings will provide the scientific guidelines for vegetation restoration and soil erosion control in rocky mountain area of northern China.

砾石（粒径≥2mm的矿物颗粒）是影响土壤水分状况的主要因素，广泛存在于土石山区土壤中，但因砾石空间分布的异质性导致其对坡面水分运移的影响研究并无统一结论，很难实现二者关系的定量准确描述。本研究拟采用野外实验观测（如染色示踪实验）与室内土柱模拟（如CT扫描、溶质运移）相结合的研究方法。通过调查不同坡向、坡位及剖面深度的砾石结构（覆盖度、含量、大小、位置等），确定砾石在坡面的空间分布特征。在此基础上，通过对土壤水文参数（容重、饱和及非饱和导水率等）、大孔隙特征（数目、直径、孔隙度等）和水分运移（地表径流、入渗、土壤水分分布、优势流等）的调查分析和实验观测，明确坡面砾石结构对土壤水文参数和大孔隙的影响，量化砾石结构与坡面水分入渗及分布、径流、优势流的关系，揭示砾石对坡面水分运移的影响及其作用机理，以期为华北土石山区植被恢复重建和水土流失防治提供科学依据。

本项目通过野外调查观测与室内土柱模拟相结合的方法，分析并揭示了华北土石山区砾石在坡面的分布特征及其与土壤水文参数、大孔隙结构的相互关系；阐明了砾石对土壤水分动态变化、地表径流、水分入渗及优势流等土壤水分运移过程的影响。研究结果显示：(1)砾石含量及覆盖度均呈现从坡上至坡下逐渐减少的趋势；(2)砾石含量与土壤水分及养分呈显著负相关性，是影响土壤水分和养分变异的主要因素，砾石含量能解释22.7%的土壤水分变异；(3)砾石覆盖抑制了水分入渗，覆盖于地表的小砾石降低了土壤饱和导水率；相反，砾石含量增加了土壤水分入渗，尤其当砾石含量大于30%，增加效果显著；(4)坡面径流随砾石覆盖度的增加而增加，但随>75mm砾石含量的增加而减小；(5)砾石含量与优势流路径数及染色深度呈显著正相关性，说明砾石促进了优势流的发生；通过室内溶质运移实验分析得出，粒径>20mm的砾石对优势流的发生有显著影响，而<20mm的砾石对优势流的影响则不显著。以上结果说明砾石对土壤水分运移过程有重要影响，在石质山区进行植被恢复与水土流失治理时应充分考虑砾石的作用与影响。