Study On Control Effect Of City Concave Herbaceous Field And Grassland On Phosphorus In Runoff

In recent years, it is more and more prominent that non-point source pollution had led to eutrophication in urban water. The issues make the research of nutrient elements quality and output characteristic become important, also the control measures. As an indispensable part of urban environment, the urban green space plays an important role in the urban non-point source pollution control. This paper chose the concave herbaceous field and grassland as the representative of the urban green space. By simulated rainfall experiments, this paper analyzed the effect of concave herbaceous field and grassland on phosphorus loss control.A device of concave herbaceous field was built in lab and simulated road runoff was put into this device. Three impact factors, which were rainstorm return period, total phosphorus load in influent and rain well ultra-high, were analyzed to study the concave herbaceous field reducing the road runoff. The concentration and form of phosphorus in overflow was measured. The result shows that:concave herbaceous field can efficiently reduce the runoff volume, the average cutting rate of volume is 46.58% when the rainstorm return period is 5 years; in all experiments, the lowest value of total phosphorus reducing rate is 58.38%; in all forms of phosphorus, the removal rate of particle phosphorus was the highest, which is 90.28%; the higher of rain well ultra-high, the lower of rainstorm return period and the influent total phosphorus load, the better of concave herbaceous field cutting total phosphorus; among the three factors, rainstorm return period had the most significant impact on cutting rate, followed by rain well ultra-high and the total phosphorus load in influent.The grassland and bara land were chosen as the study subjects, whose soil was the same. Different rain density and slope were analyzed to study their influence on generating runoff, phosphorus loss and phosphorus form in runoff. The result shows that:the proportion of runoff to rainfall, total phosphorus concentration, particle phosphorus concentration, dissolve inorganic phosphorus concentration in grassland were lower than that in bara land; grassland can ease the degree of flush happened in bara land and provent phosphorus loss. It was set up that the concept of total phosphorus reducing rate; After calculated, it was found that rain density and slope were the influence factors to TP reducing rate, which was nagative correlation with rain density and slope; when the rain density increased from 21.86 mm/h to 41.44 mm/h, the average reducing rate of TP decreased from 76.27% to 25.92% in three condition of degree.