Non-point Nitrogen Pollution In Urban Agricultural Region

The urban agriculture is the leading direction of the agricultural development in Shanghai suburb. In the process of its development, many farmers use massive chemical fertilizers to raise the volume of output, which may not only bring about the resources waste, make utilization ratio of the soil nitrogen low and induce the massive outflows, but also cause nitrogen pollution in the surface water and ground water. Study on the pollution characteristics of non-point nitrogen in urban agricultural region can provide theoretical basis for the sustainable development of urban agriculture, prevention and control of non-point nitrogen pollution, and water environmental protection.In this thesis, a typical village with urban agriculture, Orchard Village in Xinchang Town, Nanhui, Shanghai, was chosen as the research object. The contents of nitrogen in soil, surface water and ground water were continuously monitored under the different land use types, the spatial distribution characteristics of nitrogen in soil and water environment were studied, and the transfer and output characteristics of nitrogen during the typical rainfall events were analyzed. Moreover, the output load of nitrogen from the peach garden soil was evaluated by using EMC (hydrology sub-model) and SCS (hydrology sub-model) with single field rainfall flux weighted average concentration. The main achievements were summarized as follows.1. The main form of the nitrogen pollutant in the surface water and groundwater is nitrate, and the average concentrations of total (TN), nitrate (NO3--N) and NH4+-N show the obvious spatial distribution pattern in the groundwater. The average concentration of TN in the ground water was the highest nearby the river, while the lowest in the resident area. The spatial distribution characteristic of NO3--N was consistent with that of TN. The average concentration of NH4--N in the ground water in the resident area was obviously higher than that nearby the river and the peach garden. The spatial distribution of the average concentration of NO2--N was random, and not showed a remarkable variation with space. The average concentration of TN, NO3--N and NH4+-N, NO2--N in the ground water varied obviously with the time. Overall, the average concentration of the nitrogen in the ground water is higher in the rainy season, while lower in the dry season. The average concentrations of TN, NO3--N and NH4+-N are different in and around the orchard and river, and vary significantly with time in the surface water.2. The spatial distribution characteristics of nitrogen in cultivated soil in the peach garden were studied by using the traditional statistics and geo-statistics methods. The results showed that the contents of TN and NO3--N in the soil varied greater than that of NH4+-N, and the variation degrees of TN and NO3--N were higher than that of NH4+-N. The linear variogram models can be used to describe the variation of TN, NO3--N and NH4+-N contents. The spatial distribution of NO3--N and NH4+-N is patchy, while that of TN is punctate.3. The particulate and soluble nitrogen are the main outflow forms of nitrogen during the rainstorm event and heavy rain event, respectively. Nitrate was the main outflow form of nitrogen in soil during the two rainfall events. The process line of nitrogen concentration is affected by the nitrogen species, the rainfall intensity, and the rainfall amount. During the two rainfall events, the variation amplitude of NH4+-N concentration was smaller, while that of TN and NO3--N were wider. The particulate and soluble nitrogen control the outflow load of soil nitrogen during the rainstorm event and heavy rain event, respectively.4. Nitrate is the main outflow form of nitrogen by soil leakage in the conventional fertilization group, while NO3--N in 20-cm and 60-cm soil layers and depth organic nitrogen in 40-cm soil layer in the control group. The concentrations of nitrogen species in the leakage fluid in the conventional fertilization group were higher than that in the control group. The outflow concentration of nitrogen by soil leakage is affected by fertilization, rainfall, and the accumulation content of nitrogen in soil.