The Effects of Typical Hydrochemical Solutions on Quantity and Quality of Dissolved Organic Matter Leached from Agricultural Soil

As groundwater is an important irrigation source in arid area such as the North China Plain, the water chemistry may affect the migration processes of dissolved organic matter (DOM) in agricultural soil and then its quantity and quality. However, few detailed studies discussed the dynamic changes of soil DOM under electrolyte leaching process. The objectives of this study were to characterize the release and fractionation processes of DOM under dynamic leaching condition and discuss the mechanism causing DOM variations during the processes. Four typical hydrochemical solutions namely A-NaCl,B-NaHCO₃,C-Na₂SO₄, and CaCl₂ with the same concentration and similar pH were applied to a set of duplicate soil columns (at 4 centigrade). A diffusion-controlled release process observed indicated that the DOC concentration of leachate was affected by the resident duration. The DOC amounts desorbed corresponding to the solutions were in the order: NaHCO₃ >Na₂SO₄>NaCl>CaCl₂. This result could be ascribed to the presence of favoring the deprotonation and thus an increase in electrostatic repulsive, and on the other side the -bridging effect promoting the formation of mineral-organic associations and leading to a decrease in DOM desorption. Meanwhile, the measurement of UV spectrum of the effluent indicated that tended to associate with small molecules while is in contrast, more likely to bind aromatic compounds during the leaching process.