| With the development of agriculture,a large number of chemical fertilizers and pesticides have been put into agricultural production.While increasing the yield of crops,the non-point source pollutants produced by the large amount of pesticide and chemical fertilizer are flowing into clean waters with runoff and drainage,which leads to the deterioration of the ecological environment,in the water environment pollution,water pollution caused by agricultural non-point source accounts for a large proportion.Gully pond wetland can remove non-point source pollutants collected from farmland drainage through sediment interception,plant absorption and microbial degradation.Many researches on the mechanism and removal capacity of nitrogen and phosphorus nutrients to remove the wetland had finished,which fully affirms the great role of the gully and pond wetland in reducing the eutrophication of surface water.However,few studies on the effect of the hydraulic relationship between the ditch and pond system and the farmland on the removal of non point source pollutants have been studied.In this paper,the hydraulic connection between farmland and gully pond in the study area was investigated in the experimental area of the peripheral experimental field and gully pond in the Jiangdu farmland water conservancy scientific research station.The hydrological and water quality indexes(ammonium nitrogen,total phosphorus and nitrate nitrogen)were monitored at fixed point,and the distribution characteristics of the ditch and pond in the study area and the farmland and the ditch pond water were investigated.The effect of force relation on the removal of pollutants.The main research results are as follows:(1)Through the monitoring of the water quality index in 2016,the nitrate nitrogen in the pond changed little when the rice was in the growing period,and it would increase dramatically when it was fertilized,and then returned to stability with the time migration.The monitoring results of ammonium nitrogen are different,and the ammonium nitrogen is also increasing rapidly when it is fertilized,but due to its unstable characteristics,the concentration of ammonium nitrogen will rapidly decompose,the concentration is reduced rapidly to a very low concentration,and the ammonium nitrogen is at a low concentration in the period of Wheat production.The monitoring results of total phosphorus were relatively low,the maximum 0.39mg/L was during rice production,and the maximum was 0.42mg/L during wheat cropping.No matter the nitrate nitrogen,ammonium nitrogen and total phosphorus,the average concentration of the pollutant concentration in the agricultural ditch outside the experimental field is the largest,the nitrate nitrogen and the total phosphorus are of moderate variation during the period of rice,and the ammonium nitrogen is strong variability.During the period of wheat cropping,the variation of nitrate nitrogen is smaller and more stable,and the ammonium nitrogen continues the strong variation during the rice production period.(2)Considering the hydraulic connection between the ditch and the farmland,The water purification effect of gully pond is only equivalent to 70%～90%under ideal conditions.When the degradation coefficient r is very small,the realization rate e is the largest value,and the maximum of ε is 89.05%.Then ε decreases with the increase of r.When r is 0.1d-1,ε gets the minimum value,and the minimum ε is 71.45%.Then,ε increases slowly with the increase of r.(3)There is a great space for optimizing the hydraulic connection between the farmland and the ditch pond in the study area.The research area is flat,and some engineering measures can be taken to improve its hydraulic conditions so as to improve the drainage capacity of the ditch.In addition,under the condition that the area of the ditch and pond is constant,the water level can be pulled through the water level and the water depth of the drainage ditch can be increased so as to improve the water quality purification capacity of the ditch. |
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