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| DOI：10.13522/j.cnki.ggps.2017.0419 |
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| Discharge of Nitrogen and Phosphorus at Different Scales over a Small Watershed within an Irrigation District in Upstream of the Li River |
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SU Yijie, DAI Junfeng, MO Leixin, ZHANG Lihua, ZENG Honghu
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Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, Guilin University of Technology, Guilin 541004, China; 2. Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin 541004, China
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| Abstract: |
| 【Objective】 This paper is to present the results of an experimental investigation into the discharge of nitrogen and phosphorus at different scales from a small watershed within an irrigation district in the upper stream of the Li River, with a view to provide baseline data for controlling and mediating their pollution. 【Method】 We first divided Jingui Experimental Area in Qingshitan Irrigation District on the upstream of the Lijiang River into a number of sub-catchments based on DEM and ArcGIS and SWAT model. From the terrain of the river and canals, we considered five scales which were hydraulically connected. In-situ experiment was then conducted from May to December in 2016 to measure the concentration of nitrogen and phosphorus as well as their discharge rate at the outlet of the experimental area. 【Result】 The concentration of total nitrogen was scale dependent, increasing from 0.95 mg/L to 2.42 mg/L when the spatial scale increased from 335.41 hm2 to 2 798.15 hm2. In contrast, the concentration of ammonia and total phosphorus fluctuated as the scale increased, increasing fast only in the third scale, 1 135.36 hm2, and the fifth scale. The discharge of nitrogen and phosphorus was higher in irrigation season than in non-irrigation season, with the discharge of total nitrogen, ammonia and total phosphorus decreased by 54.60%, 41.64% and 55.77% respectively when the scale increased from 335.41 hm2 to 2 798.15 hm2. In non-irrigation season, the discharge of total nitrogen increased from 0.67 kg/hm2 to 2.76 kg/hm2, while the discharge of ammonia and total phosphorus fluctuated, as the scale increased. 【Conclusion】 In irrigation season, the leaching of nitrogen and phosphorus into drainage ditches and ponds as well as the reuse of the effluent reduced their discharge. However, in non-irrigation season, the area of ditches and ponds reduced by 75.10% from 55.91 hm2 to 13.92 hm2, resulting in a decrease in removal efficiency and an increase in pollutant discharge. As such, the scale-effect of nitrogen and phosphorus discharge should be taken into account in studying nitrogen and phosphorus emission and pollutant in the Lijiang River Basin. |
| Key words: nitrogen and phosphorus releases; irrigated area; scale; spatiotemporal variations; small watershed |
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