Keywords: 
• Shijiuyang constructed wetland in Jiaxing City /
• constructed root channel /
• soil enzyme /
• nutrient /
• hydraulic efficiency /
• iron /
• orthogonal design

Abstract: Root channel purification technology utilizes mixed straws with various diameters as the substrate media of constructed wetlands. This technology can promote the rapid formation of soil macropores at the initial operation stage of constructed wetlands. The novel technology had been successfully applied in Shijiuyang constructed wetland for 1.5 years. In order to evaluate the rhizospheric soil substances distribution and to compare the intercept efficiency of different constructed root channels， a research was conducted to study enzymatic activity， nutritional elements， iron element in the root channel purifying zone. The design of experiment was based on orthogonal tests， using plant straws of different species (S)， buried soil layers (L)， distance to the outer ring of straws (D) and soil apparent color around straws (C) as four experimental factors. It was found that the straws of maize and rape had begun to decompose well forming thick and thin root channels respectively， and the ambient soil around root channels was in a condition of moderate reduction. The thick constructed root channels could stimulate a better preferential hydraulic conductivity， compared to the thin ones. The soil around the thick root channels contained higher contents of nutritional elements and lower ratios of Fe2+/Fe3+. Enzyme activities were compared between soils around both straw types in the root channel zone. Results showed that phosphatase activity was higher in soil around maize straws， while urease activity and β-glucosidase activity were higher in soil around rape straws. To summarize， the thick root channels could conduct more water through the subsurface zones of wetlands and trap more elements at the initial operation stage of constructed wetlands.