黄河三角洲不同土地利用类型土壤微观结构特征

黄河三角洲不同土地利用类型盐碱土微观结构的研究,对认识该地区盐碱土的工程性质和对滨海盐碱地治理具有重要意义。该研究结合粒度分析(particle size distribution,PSD)、X射线衍射(X-ray diffraction,XRD)、压汞(mercury intrusion porosimetry,MIP)和扫描电镜(scanning electron microscopy,SEM)方法,对3种不同土地利用类型盐碱土的微观结构进行定量分析,旨在揭示其微观特性,为黄河三角洲盐碱地治理提供微观理论依据。结果表明:不同土地利用类型下的土壤黏粒含量表现大小依次为农田、滩地、草地,而土壤孔隙度大小依次为草地、滩地、农田;农田、草地与滩地盐碱土矿物成分中,石英、方解石和钠长石等原生矿物占绝对优势,仅含少量黏土矿物,且农田黏土矿物含量远大于草地与滩地;草地与滩地盐碱土孔隙特征类似,两者在0.1≤孔隙直径<10μm范围内小孔隙与微孔隙占有绝对优势,而农田盐碱土以孔隙直径在<2μm范围内的微孔隙与超微孔隙为主。农田盐碱土由致密片状、扁平状结构与微裂隙构成,骨架颗粒间由黏土矿物胶结;草地盐碱土由紧密镶嵌的块状颗粒和架空孔隙构成,骨架颗粒间无胶结;滩地盐碱土由紧密堆积的粒状颗粒和粒间孔隙构成,骨架颗粒间无胶结。研究成果可提高对黄河三角洲不同土地利用类型盐碱土微观结构的认识,为滨海盐碱地的治理、利用和开发提供了微观尺度上的依据。

Microstructure characteristics of soils with different land use types in the Yellow River Delta

Study on changes in microscopic structure of saline-alkali soil induced by different land usage in the Yellow River Delta is important to understand their consequence for soil mechanical and hydrological processes and improve soil management and remediation. This paper presents the results of an experimental study on microscopic structure of soils taken from farmland, grassland and beach at different soil depths in this region. The particle size and mineral composition of each soil sample were measured using the particle size distribution analysis and X-ray diffraction analysis, respectively. The poresize distribution was analyzed using mercury intrusion porosimetry, and soil particle arrangement and pore characteristics were measured using scanning electron microscopy(SEM). The results showed that the main particles of the three soils were silt, accounting for more than 60% of the total particle composition. The clay content in the three soils increased in the order of farmland > beach > grassland. Primary minerals such as quartz, calcite and albite were dominant in the three soils,accounting for more than 85% of their total mineral composition. The clay minerals in the three soils were dominate by illite,and the proportion of the clay minerals was less than 15% of the total mineral composition. The clay mineral content was higher in the farmland soil than in the grassland and beach soils and, as such, the mineral composition alone cannot explain the low permeability of the soils. The porosity of the farmland, beach and grassland soils was 25%, 32.58%-39.94% and 40.84%-46.16% respectively. With increasing depth, the porosity of the grassland and beach soil increased, whereas the change in farmland soil porosity did not show an identifiable trend. The pore characteristics of the grassland and beach soils were similar, while the farmland soil was dominated by micropores and ultra-micropores with pore diameter less than 2 μm. The specific pore surface area of the farmland soil was considerably larger than that of grassland and beach soils, with the adsorption capacity of the former much higher than that of the latter. Farmland soil was densely structured;it was dominated by micro-fissures, with disordered structures formed between the skeleton particles;its basic structural units were flat and flaky particles;the skeleton particles ware dominantly surface contact while the particles were cemented by clay minerals. The microstructure of the grassland soil was closely inlaid particles with a "brick-wall" arrangement, and the particle connection was mainly surface contact;it was composed of closely inlaid massive particles and overhead pores;there was no cementation between its skeleton particles. The beach soil was composed of closely accumulated granular particles and intergranular pores;there was no cementation between skeleton particles. These results improved our understanding of the changes in microscopic structure of saline-alkali soils in response to land usage in the Yellow River Delta. They provide guidance for remediation,utilization and development of coastal saline-alkali soil in the Yellow River Delta.