Abstract: Through tracer tests, the hydraulic efficiency of four kinds subsurface flow constructed wetlands with different inflow configurations (i.e., common horizontal flow and 3 kinds of multi-inflow) was examined, with the spatial variation of total nitrogen (TN) and ammonium nitrogen (NH⁺₄-N) in the wetlands and the correlation between the hydraulic efficiency and the nitrogen removal efficiency studied. Among the four inflow configurations, step-inflow had the highest hydraulic efficiency, because it had a long mean resident time and low residence time distribution (RTD), revealing that the flow pattern was much closer to a plug flow with weaker vertical mixture. Under the four inflow configurations, the TN and NH⁺₄-N showed stratified distribution, and TN varied obviously as a result of different inflow configurations. The step-inflow was in favor of the denitrification in the back end of the wetland bed. There were significant relationships between hydraulic efficiency and TN removal efficiency, while hydraulic efficiency did not affect the removal of NH⁺₄-N significantly.

Key words: Guangdong, Soil organic reserves, Soil carbon density, GIS