三峡库区典型土壤酸碱缓冲性能及其影响因素研究

受酸沉降和化肥施用等外源性酸输入的影响,三峡库区土壤面临着严重的酸化威胁。通过选取三峡库区两种典型土壤(紫色土和黄壤)作为研究对象,采用酸碱滴定法对土壤酸碱缓冲性能及其影响因素进行了研究。结果表明:在一定的p H范围内,紫色土(p H 6.5~2.5、6.2~11.5)和黄壤(p H 5.6~2.8、5.5~10.7)的p H变化与外源性酸、碱加入量均呈线性相关关系。通过分段拟合获取的缓冲容量结果显示,紫色土酸、碱缓冲容量分别为101.3、34.6 mmol/kg;而黄壤酸、碱缓冲容量分别为105.3、38.0 mmol/kg。黄壤和紫色土主要受碳酸钙与阳离子交换的缓冲作用;缓冲体系及初始p H、机械组成等土壤理化性质的不同是导致库区典型土壤酸碱缓冲容量差异的主要原因,总体表现为黄壤酸、碱缓冲性能略优于紫色土。此外,由于近年来酸沉降和氮肥用量的增加,使得库区土壤面临的酸化威胁呈上升趋势。该结果对库区土壤环境容量和典型土壤酸化潜势等研究具有参考价值,还可为区域外源性酸临界值评估以及应对策略制定提供理论依据。

ACID AND ALKALINE BUFFERING CAPACITY AND ITS INFLUENCING FACTORS OF TYPICAL SOILS IN THE THREE GORGES RESERVOIR AREA

Exogenous acid input, such as acid deposition and chemical fertilizer, have contributed to the serious soil acidification in the Three Gorges Reservoir. In this study, the titration curve method was adopted to investigate the pH buffering capacity (pH BC) and influencing factors of typical soil (purple soil and yellow soil) in the Three Gorges Reservoir. Linear regressions were used to fit the linear portion of each titration curve and the slopes of these lines were used as the determination of pH BC. The results indicated that in a certain pH range (purple soil:pH 6.5-2.5, 6.2-11.5, yellow soil:pH 5.6-2.8, 5.5-10.7), the pH changes of the two soils showed linear correlations to the amount of acid or alkali addition. Furthermore, the slope-derived pH BC of acid and alkali of purple soil were 101.3 mmol/kg and 34.6 mmol/kg, respectively, lower than that (105.3 mmol/kg and 38.0 mmol/kg) of yellow soil. The pH BC was mainly affected by the content of calcium carbonate and cation exchange capacity (CEC). The difference between pH BC of the two soils was due to their different soil buffer systems and basic properties (initial pH, mechanical composition). Above all, the pH BC of the yellow soil was slightly better than that of purple soil. Meanwhile, acid deposition and nitrogen fertilizer application can threaten soil acidification in the Three Gorges Reservoir. According to the input speed of exogenous acid, a rough estimation of the time of acidification to different pH value could be made. For purple soil, the time acidified to pH of 5.5 (which is defined as acidification) was 194 a, to pH of 4.5 was 252 a, while the time acidified to pH=4.5 of yellow soil only needed 97 a. Excessive and unreasonable nitrogen fertilizer can change the soil CEC, SOC content and soil environmental factors, decline the soil pH and soil buffer capacity, even may speed up the rate of soil acidification. This study obtained preliminary results on pH BC and the influencing factors, however, water level fluctuation in the Three Gorges Reservoir has great impacts on the physical and chemical properties of soil. In the forthcoming studies, the evolution process of the acid and alkali buffer could be of great interests in further investigations in the Three Gorges Area. The knowledge on pH BC and influencing factors of the typical soils in the Three Gorges Reservoir, could not only be conducive to improve our understandings on soil environmental capacity and the typical soil acidification potential, but to provide theoretical basis for assessing regional exogenous acid critical value.