Impact of Simulated Irrigation with Treated Wastewater and Saline-Sodic Solutions on Soil Hydraulic Conductivity, Pores Distribution and Fractal Dimension

摘要

Irrigation with treated wastewater which has the characteristics of higher salt content, larger sodium adsorption ratio (SAR), and more organic matter and suspended particles can cause the deterioration of the soil environment. Ordinary water, treated wastewater, and saline-sodic solutions with SAR = 3, 10 and 20 (mmol_cL~(-1))~(0.5), respectively, were used as five irrigation water types, and the changes of soil saturated hydraulic conductivity (K_s), soil pores distribution, and soil pores single fractal dimension (D_m) were studied after simulated irrigation for 1 and 2 years with simulated irrigation systems, which consisted of soil bins and simulated evaporation systems. The results showed that soil K_s in the following descending order: CK ＞ SAR3 ＞ WW ＞ SAR10 ＞ SAR20, and the adverse effects on soil K_s caused by suspended solid particles and dissolved organic matter might play a more significant role than sodium in treated wastewater. The 0-5 cm soils had a smaller single soil pore area but larger pores quantity after simulated irrigation, the distribution of soil pores which was irrigated with treated wastewater had a smaller change compared with saline-sodic solutions treatments, and it showed the soil pores structure binary image was an effective method to analysis soil pores distribution. Soil D_m increased after simulated irrigation, and the smallest was the soil simulated irrigation with treated wastewater for 1 year, because the plugging and filling of suspended particles and dissolved organic matter in treated wastewater made the soil pores well distributed, but the soil D_m did not increase with increasing of SAR levels in irrigation waters. The relative SAR levels irrigation to soils and soil K_s had a good linear correlation relationship, while the relationship between soil D_m and the relative SAR levels irrigation to soils was very complicated. The soil D_m which calculated from soil binary images could not well reflect the hydraulic conductivity of saturated soil. Irrigation with treated wastewater had a greater effect on soil K_s than soil D_m, comparing with saline-sodic solutions which had the similar SAR value. It was suggested that the future research should consider both the horizontal and vertical directions of soil D_m to well reflect the soil K_s.