Reduction Of Non-Point Source Pollution From Paddy Fields Through Controlled Drainage In An Aquatic Vegetable Wetland-Ecological Ditch System

Nitrogen and phosphorus losses through runoff from paddy fields are the main sources of non-point pollution in South China. Wetlands with non-food aquatic plants and ditches are used separately in many countries to reduce agricultural non-point pollution. In a field experiment conducted in the Taihu Lake Region of South China, an aquatic vegetable wetland-ecological ditch system (AWDS) with controlled drainage was constructed to purify the drainage from paddy fields. Concentrations of TN, TP, NH4+-N and NO3--N in the AWDS decreased exponentially during the purification period. After 12 days of abatement, TN and TP concentrations in the outflow of the AWDS significantly decreased by 76.7 and 34.1% respectively compared to those in the inflow. In addition to the decrease in pollution concentration, the controlled drainage contributed to lower drainage from the AWDS. TN and TP loads were reduced by 90.9 and 77.8% respectively. After a growth period, nitrogen and phosphorus uptake of aquatic vegetables in the AWDS was 274 and 24.0 kg ha(-1). After harvest, nitrogen and phosphorus contents in the soil increased in the AWDS compared with the contents before planting. The AWDS combined with controlled drainage practices seems to have the desirable functions to reduce non-point pollution. Copyright (C) 2016 John Wiley & Sons, Ltd.