四川地区天然气开采对土壤渗透性的影响

Effects of gas exploitation on soil infiltration characteristics in Sichuan province

土壤的渗透性是评价土壤涵养水源功能的重要指标之一,为明确天然气开采不同工程类型扰动后对土壤层的不同年限水文生态效应及其水源涵养功能的影响,以天然气开采为例,分析其建设活动对3类地貌类型、4种工程类型、4段年限内的研究区样地土壤渗透系数的影响情况。采用相关性分析及回归分析方法,分析天然气开采对土壤渗透系数的影响。结果表明:1)天然气开采对土壤渗透系数有一定的影响,但是这种影响随着建成年限的增长而逐渐减弱,到第5年基本得以恢复;2)通过对不同地貌、不同工程类型的土壤渗透系数随年限变化情况进行拟合,表明采用3次多项式拟合效果最好,R2均大于0.95,与实测数据有极显著的相关性,可用来预测渗透系数未来的变化趋势;3)渗透系数与土壤的化学性质相关性方面全氮最为显著,与土壤的重金属含量相关性方面铅最为显著。

[ Background] The goal of this study was to determine the effects of gas exploitation on soil infiltration. Soil infiltration capability is one of the most important indexes used to assess the effect of soil in water conservation, which depends on many internal and external factors, and is closely correlated with types of landform, types of project area, types of soil and so on. It is also a key factor in modeling soil water movement and erosion process. [ Methods ] Selecting 2 gas fields in Sichuan as the research target, we analyzed the effects of construction work during gas exploitation on soil infiltration coefficient in 3 types of landform （mountain area, hilly, and plain） , 4 types of construction area （ well site, sewage lagoon, roadway, pipeline, and contrast） and 4 different time periods （0- 1, 1 -5, 5 -10, and 〉 10 years） , and used bare land as a control; 2 -3 samples were collected in each landform and each project area per period, thus totally 150 samples were obtained. The infiltration coefficient in each sampling site was determined in field according to national standard by measuring accumulative water quantity, and the chemical properties of the samples were measured based on the national standard of environmental quality. The principal component analysis were used to analyze the correlations of them, i. e. , the effects of gas exploitation on soil infiltration coefficient. [ Results] 1 ） Gas exploitation caused certain effects on soil infiltration coefficient, but such effects were gradually reduced over time and completely recovered in the fifth year after construction. 2） The infiltration coefficient over time in different types of landforms and projects were fitted, and the results revealed that the fitting effect was the best using the cubic polynomial with the R2 〉 0. 95, showing a significant correlation between measured data, and it could be utilized to predict the change trend of the infiltration coefficient in the future. 3 ） Regarding the correlation between soil infiltration coefficient and the chemical properties of soil, it was in the most significant with total nitrogen content ; while on heavy metals of soil, Pb content was the most significantly correlated with the infiltration coefficient. Using soil chemical composition factors and representative factors as the independent variables of soil heavy metal content and soil infiltration coefficient as a dependent variable, the equation of variables was established. The correlation analysis of the impact of soil chemical properties and the heavy metal content factors on soil infiltration coefficient showed that the mass fraction of organic, total nitrogen, arsenic and lead had significant effect on soil infiltration coefficient. The principal component regression of significant impact factor showed that the mass fraction of total nitrogen was maximum, which played leading roles in the impact of soil chemical properties on soil infiltration coefficient; the mass fraction of lead had outstanding performance with regard to the heavy metal content.