Function Of Paddy Field Wetland To Absorb Non-point Source Pollutants

The occurrence of eutrophication is closely related to soil nitrogen and phosphorus nutrient losses.The migration and transformation of both nitrogen and phosphorus nutrients in surface runoff can be greatly affected by paddy field.In this study,a typical cropping system was selected to study the laws of N and P output in surface runoff under different time and rainfall conditions.Two different rice varieties were selected as paddy field wetland crops,and their effects on rice yield,surface water,soil phosphorus forms,and soil microbes were studied by means of nuclear magnetic resonance(NMR)and high-throughput sequencing.The objective of this study was to provide a reference for the establishment of a paddy field wetland system with high phosphorus removal efficiency.The results are as follows:(1)Four samplings were conducted in different seasons.Three sampling results(January 13th,May 15th and September 29th)showed that the concentrations of nitrogen and phosphorus at the outlets were all lower than those at the inlets,indicating that the paddy field wetlands could reduce the concentration of pollutants by dilution,so as to purify the water quality.The dissolved nitrogen was the main form of nitrogen at both the inlet and outlet,and accounted for 48.64%?99.51%and 67.72%?98.32%of total nitrogen at the inlet and outlet respectively.The average proportion of dissolved phosphorus was 58.66%at the inlet,while 43.97%at the outlet.(2)From the result of the sampling in September 29th,nitrogen was consumed by paddy field wetland and the capacity of consumption was 21.58 g N/(4h·ha).From the results of sampling in May 15th and September 29th,phosphorus was consumed by paddy field wetland and the capacity of consumption were 0.67 g P/(4h·ha)and 2.97 g P/(4h·ha)respectively.During other sampling times,paddy field outputted nitrogen and phosphorus.These results showed that most nitrogen and phosphorus were consumed by paddy field wetland in the medium and latter stages of rice growth.(3)By comparing two rice varieties(conventional variety:Xiushui 134;variety developed by Zhejiang University:Yudaoyihao),it was found that Yudaoyihao absorbed more carbon,nitrogen and phosphorus than Xiushui 134,which were stored in rice straw.The average amount of straw was 12.62 t ha-1 in Yudaoyihao,40.3%more than that of Xiushui 134,and no significant difference in paddy yield was observed.The amount of carbon,nitrogen and phosphorus accumulated in straw were 4880.54 kg ha-1,173.80 kg ha-1 and 14.25 kg ha-1,which were all significantly higher than those in Xiushui 134(3407.89 kg ha-1,108.56 kg ha-1 and 8.42 kg ha-1).No statistically significant difference of the amount of carbon,nitrogen and phosphorus were found in paddy rice during the two rice varieties.(4)There were more carbon,nitrogen and phosphorus remained in soil during the mature stage of Xiushui 134,which showed that Yudaoyihao could absorb more nutrients in soil.Results of high-throughput sequencing indicated that the rice variety YD-1 had no significant effect on the dominant bacterial communities in paddy wetland soils.The change of bacterial community diversity was mainly caused by the change of non-dominant species.The network analysis showed that there were only a simple network module among soil Total-P,soil bacteria and rice straw biomass.Network relationships among the soil pH,Total-C,Total-N,Straw-N,Grain-N,and Grain-P were part of a different module than the network that included Total-P.