A field-scale observation method for non-point source pollution of paddy fields

In order to eliminate the limitations of conventional field-scale observation methods for non-point source (NPS) pollution, this paper proposes a direct method to observe NPS pollution from paddy fields. The evapotranspiration (ET) and infiltration loss hydrographs of paddy fields in different stages of growing season are estimated depended on observed water-depth hydrograph, rainfall hydrograph and irrigation data. And outflow hydrograph of paddy fields is analyzed through water balance approach. Combined with observed surface water quality data, loads of NPS pollution in outflow from the paddy field can be derived. The proposed method can be applied to quantificational observation of NPS pollution from paddy field in the condition of multi-outlets and dynamic variation of the lowest outlet height during growing season, which is impossible to conduct field observation by using conventional methods. The proposed method reduces the uncertainty of runoff observation and is more operable.