旱地和水田土壤DOC吸附-解吸对pH的响应

为揭示pH对农田土壤DOC吸附-解吸的影响,以亚热带红壤区旱地和水田土壤为研究对象,采用室内模拟实验,对两种土壤添加不同DOC量后分别在pH 4、pH 6和pH 8条件处理下的吸附和解吸试验进行研究,分析不同pH反应条件下土壤对DOC的吸附和解吸过程,并计算土壤对DOC吸附和解吸的参数,探讨DOC吸附和解吸对pH的响应,初步探析吸附对DOC组成的影响。结果表明,同一土壤在pH 4、pH 6和pH 8条件下对DOC的吸附量差异显著(P0.05)。随着DOC初始浓度的增加,在pH 4、pH 6和pH 8条件下旱地土壤对DOC的平均吸附量为4.90、2.98和8.86 mg/g,水田土壤对DOC的平均吸附量为4.12、3.10和8.90 mg/g。土壤DOC吸附方程的拟合效果受到pH的显著影响。吸附平衡后,DOC溶液的单位吸光度值E254、E260、E272和E280(芳香性、疏水性组分)的变化率随pH增加而降低。两种土壤对DOC芳香性、疏水性组分的吸附能力受土壤类型影响较小,但受土壤环境pH的影响显著。两种土壤对DOC的解吸量随pH升高而降低。酸性条件下(pH 4),DOC的净吸附量旱地土壤显著大于水田土壤,但在pH 6和pH 8时两种土壤的净吸附量差异不显著。由于红壤区两种土壤多呈酸性,这可能是造成红壤区旱地和水田土壤DOC含量差异的主要原因之一。

Response of adsorption and desorption between upland and paddy soils and dissolved organic carbon to pH

In order to reveal the influence of pH on DOC adsorption and desorption in farmland soil, the upland soil and paddy soil in subtropical red soil region was investigated in this paper. The experiment of DOC adsorption and desorption of two soils was investigated at pH 4, pH 6 and pH 8 treatments. The parameters of DOC adsorption and desorption in soils under different pH were calculated. The response of DOC adsorption and desorption to pH and the change of the components of DOC were explain after adsorption. The results showed that the adsorption capacity of DOC in the same soil was significantly different (P<0.05) under the conditions of pH 4, pH 6 and pH 8. With the increase of the initial concentration of DOC, the average amounts of DOC adsorption were 4.90, 2.98 and 8.86 mg/g respectively at pH 4, pH 6 and pH 8 in upland soil, and were 4.12, 3.10 and 8.90 mg/g respectively in paddy soil. The fitting effect of equation of DOC adsorption was significantly affected by the pH. The change rate of E254, E260, E272 and E280 of DOC which express aromatic, hydrophobic component of DOC decreased with the increase of pH in adsorption equilibrium solution. The adsorption capacity of aromatic and hydrophobic components of DOC was slightly affected by soil type and strongly affected by the pH. The desorption capacity of DOC decreased with the increase of pH in two types of soil. The net adsorption amount of DOC on upland soil was significantly higher than that on paddy soil in acidic condition (pH 4), but no significant difference between the two types of soil at pH 6 and pH 8. The upland and paddy soils of red soil region were mostly acidic, which may be one of the primary causes for DOC content discrepancy in two types of farmland soil of red soil region.