Abstract:

In order to study nitrogen removal in vertical infiltration of runoff by artificial green belt near urban riparian,a micro catchment area was constructed at Changfeng green belt of Suzhou River riparian. Meanwhile permeability of Changfeng green belt was measured by double ring method and soil samples were collected for analysis of physicochemical properties. In situ pore water samplers were used to collect samples of vertical infiltration at different depth in the micro catchment area,which were distributed from surface runoff flowing 1 m,11 m,18 m,21 m at depth of 30 cm,60 cm and 90 cm. 3 pore water samplers were buried at each depth. The water in Suzhou River containing higher nitrogen concentrations than the corresponding type Ⅴ standard values of the GB 3838-2002 National Environmental Quality Standards for Surface Water was fit to simulate runoff. Therefore,5 rainfall runoff stimulation experiments were carried out at Changfeng artificial green belt using water of Suzhou River at October,November of 2010 and April,June,August of 2011. Spatial variation of nitrogen in vertical infiltration and removal rate by artificial green belt were analyzed and compared. The results showed that the permeability of Changfeng green belt was 0.9 mm/min,which was medium in urban green belt of Shanghai. The physicochemical properties of the soil samples showed a distinct spatial difference. So Changfeng green belt was a typical municipal green belt. There was significant removal for nitrogen in vertical infiltration of runoff by artificial green belt of riparian,particularly in the layer at 0-30 cm in each experiment. Removal rates of TN and NH4+ by soil in layer at 0-30 cm were above 39.9% and 39.8% respectively. But the accumulative removal rates at 0-60 cm decreased due to the increase of nitrogen concentrations in vertical infiltration at the depth of 30-60 cm. The nitrogen concentrations in layer of 60-90 cm descended which caused the accumulative removal rates at 0-90 cm higher than those at 0-60 cm. Compared with the stimulated rainfall runoff,i.e.,the water of Suzhou Creek,the infiltrated water samples collected at different depth had a different nitrogen composition. The percentage composition of NO3-+NO2- in TN increased in the vertical infiltration,but the NH4+ was quite the contrary. There was conspicuous spatial variation of nitrogen in vertical infiltration at different sites in catchment area. With the increase of flow distance of surface runoff,concentration of nitrogen in vertical infiltration in layer at 0-30 cm would firstly increase and then decrease. Nitrogen removal rate of green belt would decrease with the waterlogging time increasing. The nitrogen removal rates varied with month. There were higher removal rates in April and October because there were suitable climate and edaphic condition. Removal rates of TN,NH4+ and NO3-+NO2- by soil in layer at 0-30 cm exceeded 63.5%,89.1% and 41.6% respectively in April and October. In general,urban riparian zone,which was made up of artificial green belt,could remove much nitrogen and be an important parclose for nitrogen discharged into groundwater and urban rivers by vertical infiltration of runoff