Abstract: The interaction between dissolved organic matter (DOM) and soil colloidal particles will control the aggregation process of purple soil colloid, which further play an important role in soil and water conservation in the Three Gorges Reservoir Area. The effects of DOM concentrations on the zeta potentials and aggregation processes of colloidal particles,extracted from three types of purple soils in the Three Gorges Reservoir Area, were respectively determined by the zeta potential meter and light scattering techniques. The results show that (1) The aggregation of three purple soil colloids exhibited a conversion from slow aggregation (linear growth) to fast aggregation (power function growth) with increasing DOM concentrations. The total average aggregation rates (TAA) of the three purple soil colloids were significantly different, and the critical aggregation concentration (CCC) of neutral, alkaline and acidic purple soil colloids were 4.74, 2.72 and 1.77 mg·L^-1, respectively, and the CCC of neutral purple soil colloids was 1.74 and 2.68 times those of alkaline and acidic purple soil colloids, respectively. (2) With the increase of DOM concentrations, zeta potentials of neutral, alkaline and acidic purple soil colloids decreased from -20.08, -18.89 and -16.44 mV to -10.60, -6.86 and -5.62 mV, respectively. As a result, the electrostatic repulsive potential energies between colloidal particles decreased with decreasing zeta potentials (absolute value). Meanwhile, critical DOM concentration values existed for the variation of zeta potential of the three purple soil colloids, which were 5.0, 2.5 and 1.7 mg·L^-1, respectively, basically consistent with the CCC values. At the same DOM concentration, zeta potential (absolute value) of the neutral purple soil colloids was the largest, followed by that of the alkaline purple soil, and the acidic purple soil. (3) Activation energies for the three purple soils colloids aggregation decreased continuously with increasing DOM concentrations, in particular, the decreasing trend of activation energies was more obvious in the lower concentration range. Given the same DOM concentration, activation energies for aggregation showed the order of neutral purple soil > alkaline purple soil > acidic purple soil. With changed DOM concentrations, zeta potentials, activation energies as well as CCC values for purple soil colloids aggregation varied to some extent, thereby affecting the aggregation processes of purple soil colloids.

Key words: colloidal particle, Three Gorges Reservoir Area, dissolved organic matter, aggregation