Analysis of nitrogen and phosphorus dynamics in a paddy field-ditch-pond system in a typical polder area of southern China

As an effective measure for retaining paddy drainage and control agricultural non-point source pollution, the paddy field-ditch-pond system can buffer nitrogen and phosphorus pollutants in field drainage. Few studies have investigated the spatiotemporal dynamics of nitrogen and phosphorus across an integrated paddy field-ditch-pond system in polder landscapes. So in this paper, water quality monitoring through a paddy field-ditch-pond system were conducted in a typical polder area of southern China. Total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3−-N) and orthophosphate (PO43−) of the paddy field-ditch-pond system were measured during the growth periods of paddy rice. The temporal and spatial distribution characteristics of nitrogen and phosphorus were analyzed. The results showed that the concentrations of TN and TP ranged from 1.31 to 3.54 mg·L− 1 and 0.038 to 0.14 mg·L− 1, respectively, in the drainage ditches during the paddy rice growth period. The concentrations of TN and TP varied between 0.11 ~ 4.90 mg·L− 1 and 0.02 ~ 0.22 mg·L− 1 in the ponds, respectively. The concentrations of TN, NH4+-N, NO3−-N, TP and PO43− in paddy fields, drainage ditches and ponds showed a decreasing trend from paddy fields to drainage ditches and ponds. The ditch-pond subsystem had a certain interception and purification effect on nitrogen and phosphorus of paddy field drainage water. In the study area, setting up ecological drainage ditches, adopting controlled drainage and growing aquatic plants in drainage ditches can be taken to improve water quality. Findings from this research may provide scientific basis for precise prevention and control of agricultural non-point source pollution in the polder area.