Study On The Reduction Effect Vegetation Buffer Zone On Agricultural Non-point Source Pollution In Ulansuhai Lake

Vegetation buffer zone is located between farmland and ford.It reduces the nutrient load reaching the land-water interface through vegetation filtration,sedimentation,adsorption and infiltration.It is considered to be an effective method to reduce agricultural non-point source pollution and control nutrition pollution and degradation of freshwater ecosystems.Ulansuhai Lake is the only receiving water body for farmland drainage in the Hetao Irrigation District,but due to the problem of soil salinization,the lakeside vegetation and ecological functions have been seriously degraded.Therefore,studying the recovery or reconstruction of lakeside vegetation buffer zone is very important theoretical significance and practical application value for restoring degraded aquatic ecosystems.This research focused on the artificially constructed vegetation buffer zone in the degraded area of the saline-alkali lakeside vegetation in Ulansuhai Lake,to study the reduction effect and influencing factors of agricultural non-point source pollution.In this paper,the effects of three vegetation buffer zones(Phragmites australis,Puccinellia distans and Suaeda glauca)on the reduction of total nitrogen,total phosphorus and COD in different months were studied by small-scale experiment when the slope of buffer zone was 2°,4° and 7°.The field test was conducted to explore the removal effect and the best width selection of vegetation buffer zones(Phragmites australis,Suaeda glauca,Tamarix ramosissima and mix planting of Phragmites australis and Suaeda glauca)in different seasons when the slope was 2°.The results were as follows:(1)The reduction effect of the three slope vegetation buffer zones on agricultural non-point source pollution was as follows: with the increases of the slope,the removal effect of the buffer zone becomes lower,and 2° slope>4° slope>7° slope.When the slope was 2°,the vegetation buffer zone had the best reduction effect on agricultural non-point source pollution: the TN removal capacity of each buffer zone in runoff water was Puccinellia distans(49.87%)> Phragmites australis(43.75%)>Suaeda glauca(43.17%)> Blank(23.12%);TP removal ability was Puccinellia distans(48.60%)> Suaeda glauca(47.35%)> Phragmites australis(45.13%)>Blank(28.00%);COD removal capability was Phragmites australis(45.22%)>Suaeda glauca(41.52%)> Puccinellia distans(41.36%)> Blank(28.22%).The TN removal ability of seepage water was Puccinellia distans(77.94%)> Suaeda glauca(73.73%)> Phragmites australis(52.23%)> Blank(34.07%);the TP removal capability was Puccinellia distans(84.10%)> Phragmites australis(77.12%)>Suaeda glauca(75.70%)> Blank(32.64%);the COD removal result was Suaeda glauca(69.85%)> Puccinellia distans(65.52%)> Phragmites australis(63.38%)>Blank(36.76%).With the change of the month,when the slope was 2°,the reduction rate of TN,TP and seepage COD by the Suaeda glauca buffer zone was significantly different,the reduction rate of TP and seepage TN by the Phragmites australis buffer zone had a significant difference.(2)The results of the field test showed that the buffer zone for planting plants had a better removal effect than the blank buffer zone.The order of TN removal effect in runoff water and seepage water was Phragmites australis > Suaeda glauca >mixed planting > Tamarix ramosissima,the maximum removal rate of runoff was53.56%,and the maximum removal rate of seepage was 79.17%.The removal effect of TP in runoff water was Phragmites australis > Suaeda glauca glauca > Tamarix ramosissima > mixed planting,and the maximum removal rate was 62.37%.The removal effect of TP in seepage was Phragmites australis > Suaeda glauca > mixed planting > Tamarix ramosissima,and the maximum removal rate was 83.25%.The removal effect of COD in runoff water was Suaeda glauca > Phragmites australis >Tamarix ramosissima > planting,and the maximum removal rate was 50.53%.The removal effect of COD in seepage was Suaeda glauca >Phragmites australis > mixed planting > Tamarix ramosissima,and the maximum removal rate was 67.34%.By comparing the removal rate,Suaeda glauca and Phragmites australis can be selected as the first plants for constructing the vegetation buffer zone of the Ulansuhai Lake.(3)The field test results showed that the vegetation buffer zone in the summer growth period had a higher removal rate of pollutants(TN,TP and COD)than in autumn.According to the data of TN,TP,and COD removal rate in runoff water,the nonlinear fitting results showed that when TN,TP and COD removal rate reach50%,60% and 50%,the Phragmites australis buffer zone,the Suaeda glauca buffer zone,and the mixed planting buffer and Tamarix ramosissima buffer belt should be21 m,19 m,29 m and 25 m.Constructing a vegetation buffer zone could effectively reduce the concentration of salt ions in the soil solution,reduce the degree of soil salinization,and improve the soil quality.