| Recent years, the effective utilization rate of chemical fertilizer and pesticide for farmland is only 30% in China. Most of them following with rainfall or irrigation leak into surface runoff or groundwater that would result in water pollution. Although, many measures are employed to control agricultural non-point source pollution, the water quality of water basin which is mainly influenced by agricultural non-point source pollution is not improved. Hedgerow is an ecological isolation technology, which is widely employed to control the slope farmland nutrient elements loss in the zones between sloping land and water environment.Three kinds of plants were chosen to design hedgerow, which were often applied to eco-environment restoration, solid soil slope protection and slope greening in Sichuan province:photinia fraseri, lobular privet, and ryegrass. Firstly, four hedgerow systems, including photinia fraseri + lobular privet + ryegrass (T1), photinia fraseri+lobular privet (T2); lobular privet + ryegrass (T3) and photinia fraseri + ryegrass (T4), were designed. Then, the orthogonal experiment is used to investigate the influence of vegetation conditions, concentration of pollutants, rainfall, and slope of hedgerow on removing pollutants in runoff, and multiple regression analysis is carried out on affecting factors. Lastly, the removal efficiencies of four hedgerow systems on TN, TP, NH3-N, TOC and COD is investigated in different slopes and influent concentrations. The following results are obtained.(1) The results of orthogonal experimental show that vegetation conditions, pollutants concentration of inflow, and rainfall are significantly influenced on removal rate of TN at the level of 1%. And the influence of slope on removal rate of TN is at level of 5%. Vegetation conditions, pollutants concentration of inflow, and slope are significantly influenced on removal rate of TP and TOC at the level of 1%. and the influence of rainfall is not significant. Vegetation conditions, rainfall, and slope are significantly influenced on removal rate of NH3-N at the level of 1%. and the influence of pollutants concentration of inflow on removal rate of NH3-N is at level of 5%. Four factors are significantly influenced on removal rate of TP and TOC at the level of 1%. The results of multiple regression analysis show that there is significant linear relationship among four factors.(2) For the these 4 hedgerow systems, the removal efficiencies of all pollutants, especially TP、NH3-N and COD, decrease with the increasing of slopes. It indicate that when the slopes increase from 5 degree to 20 degree, the removal rates decrease from 52.25%～76.75% to 33.68%～60.34% for TP,36.84%～68.33% to 34.30%～45.46% for NH3-N and 13.26%～38.69% to 3.15%～26.74% for COD. But NH3-N, removal efficiencies of pollutants increase with increasing of influent concentrations. When the influent concentrations increase from low to high, the removal rates of TP, TOC, COD by the hedgerows increase from 33.33%～60.11% to 57.06%～81.44%,-0.84%～2.92% to 9.64%～17.69% and -14.75%～11.25% to 20.62%～42.33%, respectively.(3) The removal rates of TN, TP, NH3-N, TOC and COD of hedgerow systems are significantly higher than that of bare soil system. Compared with the bare soil system, the maximum removal rates of hedgerow increase from 12.81% to 47.02%,34.29% to 76.75%, 18.27% to 68.33%,-0.93%to 11.52%, and 2.31% to 38.69% in different slopes, respectively; in different influent pollutant concentrations, the maximum removal rates of hedgerow increase from 15.57% to 53.05%,37.93% to 81.44%,17.60% to 64.05%,2.92% to 17.69% and -33.40% to 11.25%.(4) In order of best removal rate of pollutants for farmland wastewater by 4 hedgerow systems, it goes:T1, T4, T3, and T2. It indicate that the removal rate of T1 (photinia fraseri+ lobular privet + ryegrass system) is the highest. The possible reasons would be that, the highest surface coverage, the developed root systems and the interaction among three plants to retard the pollutants.In conclusion, the hedgerow systems which were formed with photinia fraseri, lobular privet, ryegrass on the removal efficiency of pollutants for farmland wastewater was remarkable. They had the advantages of low cost, less investments and wide applicable scope. The results of this study provided the theoretical basis for controlling of agricultural non-point source pollution, promotion of hedgerow technology and protection of key water source places for sloping farmland, and provided a new utilized pathway on improving the quality of water environment in southwest China. |
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