(1.State Key Laboratory of HydrologyWater Resources and Hydraulic Engineering, Hohai University, Nanjing, Jiangsu 210098, China;2.Kunshan Promotional Station of Water Conservancy Technique in Jiangsu Province, Kunshan, Jiangsu 215300, China; 3.Jinxi Water Station in Kunshan, Jiangsu Province, Kunshan, Jiangsu 215324, China)
The change in nitrogen concentration and distribution feature of carbontonitrogen ratio in the agricultural ditch and wetland system were analyzed based on the observed data in fields to investigate the nitrogen removal effect from drainage water in the system under a controlled irrigation and drainage condition. Results showed that TN，NH+4-N and NO-3-N concentrations in drainage were peaking after fertilization and then were significantly reduced after agricultural ditches were made to store water, causing 63.9% 67.8% and 83.2% nitrogen removal efficiencies in TN, NH+4-N and NO-3-N, respectively. The nitrogen concentration was reduced further after the drainage water was purified in wetlands, resulting in 47.7%, 44.3% and 82.0% average removal efficiencies for TN, NH+4-N and NO-3-N. Since the influence of organic matters on water quality is little under the controlled irrigation and drainage condition, a low carbontonitrogen ratio was maintained in general. The agricultural ditch and wetland system are effective in removing nitrogen in paddy field drainage water. However, the influence of low carbontonitrogen ratio on the Nitrogen removal efficiency is little under a controlled irrigation and drainage condition.
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