广西环江流域硫污染农田的土壤酸化与酸性土壤分布

矿业活动通过多种途径将矿石中伴生的还原态硫带入土壤而导致周边土壤酸化,是目前矿山周边普遍面临的重要环境问题。本文以广西环江为例,探寻大面积农田酸化的原因和酸度分布特征。研究结果表明：矿物组成分析（X-ray）、硫形态分析（EXAFS）和同位素分析结果表明：环江农田土壤酸化的原因是洪水携带含硫尾砂进入农田,还原态硫氧化产酸导致土壤酸化。由于矿渣中还原态硫的污染,受污染土壤的酸度、铁和硫的浓度显著高于未受矿渣污染的土壤。大环江沿岸出现不同的污染特征：上游土壤的Fe,SO4^2-（SS）和St含量较高,但土壤尚未发生明显酸化;中下游农田土壤H^＋和SO4^2-含量较高,土壤发生明显的酸化现象,还存在继续酸化的风险。土壤受还原态硫污染后,如果将旱地改为水田,则可以降低土壤还原态硫的氧化速度和减缓酸化速度。

Spatial Distribution of Acid Soils in the Huanjiang River Valley,Guangxi

The reducible sulfur associated ore was brought into soil in many ways, which will further acidify its surrounding area. In the Huanjiang River of Guangxi, more than 600 hm2 of farmland have been acidified, so the formation of soil acidification and the distribution characteristics of acidity were studied. The chemical analysis results showed that soil acidification came from oxygenation of reducible sulfur. Based on the results from mineral (X-ray), sulfur speciation (EXAFS) and Pb isotope analysis, the cause for the formation of soil acidification can be found out: In 2001, the flood destroyed the tailing dam located in the upstream of the Huanjiang River, and carried the tailing into farmland, so the reducible sulfur in tailings was oxygenated into H after a certain period of time. The area on both banks of the Huanjiang River was all affected by flooding, which should be given more attention. The spatial variabilities of pH, St, SO42- (Ss), TAA, TPA and Fe in the investigated area were very large, but the contents of acidity, iron and sulfur in flooded soil were much higher than those in the unflooded soil. The soil near mining sites was not acidified because of secondary pollution by alkaline tailings, but has potential acidification risk; while the soil in mid- and down-stream of the river had been acidified more or less, and most soil still has potential acidification probability. It is supposed that acid pollution was more serious in dry soil than in paddy soil, so converting dry land into paddy land could decrease the oxidative rate of reducible sulfur.