Water Quality Modeling for Wetland and Ecological Ditch to Treat Drainage Water from Paddy Fields

LIU Xinjingyu; WANG Xiugui; TIAN Ying; HAN Xudong; LI Zongli; WANG Tanghai

doi:10.13522/j.cnki.ggps.2017.0239

Abstract：Agricultural non-point source pollution (ANSP) is becoming increasingly serious because of large amount of drainage water discharged from farmland, especially from paddy fields for its flooding irrigation and the application of excessive fertilizer.[Objective]Reduce the pollution of paddy field drainage.[Method]The ecological ditch and constructed wetland were taken as an approach to treat the drainage water from the paddy field, and a pilot area in Xianrendu Town, Xiangyang City, Hubei Province was chosen as the research subject. Water quality models of ecological ditch and wetland were developed and the drainage water qualities were simu-lated for different scenarios.[Result]①Combination of ecological ditch and constructed wetland was an effec-tive approach to treat drainage water quality and field water logging;②The best location was to set the construct-ed wetland at the drainage system outlet for the purification of drainage water;③According to the water purifica-tion effect of per unit area in the horizontal, the constructed wetland in the main drainage channel outlet was the best one, followed by the wetlands in lands conneted to drainaige channel, and the dainage channel was the least one, and their equivalent area ration was 1:8.4:938.5;④In suggested scenarioⅢ, the purification of drainage water contribution rate of ecological ditches, natural wetland and constructed wetland were 2.9％, 30.3％ and 66.8％, respectively. The sensitive analysis of ecological ditche parameters showed that, there was almost no ef-fect on water purification when the longitude slope varied from 1/2000 to 1/5000 and roughness varied from 0.025 to 0.04 of the ecological ditches.[Conclusion]As far as total nitrogen concentration is concerned, it is more land-saving to replace natural wetland with farmland, and bulid constructed wetland at the drainage system outlet.