| The agricultural non-point pollutants have become important source of nitrogen and phosphorus in water. For the purpose of reducing nutrient loads of downstream water and improving environmental quality, so it is necessary to construct the control technology system of ecological ditch on agricultural non-point source pollutants of catchment headwaters. Ditch, as the initial convergence of agricultural and rural sewage, is always the channel of the agricultural non-point pollutants into river.In order to effectively intercept the agricultural non-point source pollutants such as nitrogen and phosphorus, this experiment choosed the subtropical red soil watershed ditch system as the main study subject. First, did the research on the ecological ditch which planted ornamental aquatic plants of Canna glauca, Hydrocotyle vulgaris, Sparganium stoloniferum. Myriophyllum verticillatum. Juncus effusus. etc. Then, discussed transportation and transformation of nitrogen and phosphorus in ecological ditches in rainfall conditions and the effects of ecological ditch on interception of agricultural non-point pollutants by the monitoring of nitrogen and phosphorus changes in water-sediment-plant system.determination of plant photosynthetic characteristics, plant harvesting management and sediment phosphorus adsorption experiment of ecological ditches of different plant area and the original natural ditch. Meanwhile, did the research on the other ditch of this this area, which are Feiyue ditch which planted Ponlederia cordata, determined the best time of Pontederia cordata to harvest and compared the effect of purification water of Pontederia cordata ditch (eco-ditch) and natural ditch through analyzing the raining influence on the nitrogen and phosphorus losing, and revealed the transportation and transformation of the nitrogen and phosphorus in the ditch in rainfall conditions. At last, did the research on the ecological benefits and economic benefits which using the aquatic plant after harvesting to cover tea garden produced. It provided ways and thought for the utilization of Aquatic plants. The main conclusions were as follows:1. The changes of total nitrogen, total phosphorus content of ecological ditch in irrigation or raining condition and seasonal changes(1)The total nitrogen, ammonium nitrogen content were at their highest in irrigation or in3d after the rainfall, and phosphorus were content at their highest in irrigation or in2d after the rainfall. The total nitrogen, total phosphorus decreased gradually at different sections after the rainfall.(2)In the water seasonal change, the highest content of total nitrogen, ammonium nitrogen and total phosphorus is in winter.(3)The removal rates of total nitrogen and total phosphorus in water of ecological ditch were64%and70%. respectively.2. Aquatic plants absorbing, intercepted sediment and the removal amounts of nitrogen and phosphorus the whole year in ecological ditch(1) Different aquatic plants could take away nitrogen and phosphorus scope20.34-109.12g.m-2、3.41～17.95g.m-2the whole year. Myriophyllum verticillatum and Canna glauca had the strongest absorbing capacity among them, especially during their harvest time, and they had been choose as the optimizing plant used in ditches.(2)Canna glauca, Sparganium stoloniferum and Juncus effusus had the strongest capacity on intercepting sediment as they have huge roots. Hydrocotyle vulgaris and Myriophyllum verticillatum also had the interception effect on sediment because of their stolon. Every year. The intercepted sediment cumulant and the cumulant of total nitrogen and total phosphorus of different plants have range of variation:86.68～106.78kg.m-2、66.94～92.78g.m-2and24.51～47.23g.m-23. Correlated relationship between net photosynthetic rate and nitrogen and phosphorus removal efficiency in ecological ditch(1) the net photosynthetic rate of Hydrocotyle vulgaris and Canna glauca changed in a double-peak curve, both of them appears a photosynthetic "midday depressions" at noon; but the Canna glauca’s net photosynthetic rate was greater than the Hydrocotyle vulgaris s.(2) stomatal conductance (Gs) and photosynthetically active radiation (PAR) were the important factors that affected the Hydrocotyle vulgaris’s net photosynthetic rate, and the stomatal conductance(Gs) was the main affective factor for the Canna glauca’s net photosynthetic rate.(3) Both plants’ net photosynthetic rate had obviously positive correlation with ditch nitrogen’s purifying effect, while had no obviously relationship with phosphorus removal rate.(4) Based on all the patterns above, the net photosynthetic rate of aquatic plants could be one of the important basis and the Canna glauca could be the best choice.4. The aquatic plants harvesting on affects of removal of nitrogen and phosphorus of ecological ditch sediment and water(1) In addition to Sparganium stoloniferum, the harvest could improve the removal rate of nitrogen and phosphorus in sediment of other aquatic plants. Compared with the non-harvested plot, the harvest could improve the removal rate of sediment total nitrogen and phosphorus in the following order:Canna glauca>Myriophyllum verticillatum> Hydrocotyle vulgaris> Juncus effusus>Sparganium stoloniferum.(2) In addition to Sparganium stoloniferum, cutting aquatic plants could improve the removal rate of TN and TP in water.5. The sediment physicochemical properties and phosphorus sorption capacities in ecological ditch(1) In compared with ditch soil in the original drainage ditch, the physicochemical properties of ditch soils from the novel constructed ditch had obvious vertical distribution; Among the five study plants, vegetation of Canna glauca, Hydrocotyle vulgaris and Myriophyllum verticillatum in the novel drainage ditch quickly increased TOC content of ditch soils.(2) The Freundlich equation modeled soil sorption isotherms was better than the Langmiur equation;P adsorption capacity in ditch soils with Hydrocotyle vulgaris and Myriophyllum verticillatum had higher KF and Smax than those with other three study plants.and ditch soils from the novel drainage ditch had higher P retention capacity than that from original drainage ditch.(3) The ecological ditch converted in agricultural area has better interception effect of the phosphorus loss than the natural ditch;The results indicated that the ditch soils vegetating with proper plants was available for further P adsorption and could be P sink, which had more significance for reducing P loss risk in agricultural headwater catchment.6. Interception effect of nitrogen and phosphorus of Pontederia cordata ditch in Feiyue ditch(1) Eco-ditch(Pontederia cordata ditch) and natural ditch could purify nitrogen and phosphorus contents of water, and reduction range (3.37%-33.33%) of total nitrogen and total phosphorus was higher than reduction range (-3.66%-7.14%) of nitrate and ammonium nitrogen, the interception capacity of eco-ditch (6.82%-33.33%) was obviously higher than natural purification of natural ditch (-3.66%-16.67%).(2) After raining the content of total nitrogen and nitrate nitrogen in ditch water had the tendency of increasing firstly and then declining, while the content of ammonium nitrogen was unstable, the content of total phosphorus reached highest values after raining the2nd, then tended to steadily.(3) Seasonal dynamics of the contents of aboveground nitrogen, phosphorus and biomass of Pontederia cordata reached highest values in October, so, it was the best time to harvest. The content of the aboveground nitrogen, phosphorus was28.38g.kg-1and4.10g.kg-1and biomass was0.19kg.m-2.The harvest of Pontederia cordata would remove5.36g.m-2of nitrogen and0.78g.m-2of phosphorus every year, the objective is to provide the theory basis for restoration application of the development ornamental plant in ditch.7. Resource recycling utilization of aquatic plant after harvestAquatic plant after harvesting not only take a lot of nitrogen and phosphorus pollutants, but also may be this nutrient muching. recycling utilization and coverage of the tea plantation.(1) Covering Aquatic plants in the tea plantation could improve the physical and chemical properties of the soil, it obviously increased the content of the soil layer (0-20cm) organic material, total nitrogen, total phosphorus, alkali-hydro nitrogen and available phosphorus, meanwhile, increased the content of Soil microbial biomass nitrogen and phosphorus. The soil nutrient declined with the increase of the depth.(2) Covering Aquatic plants in the tea plantation could prevent the dominant species of weeds, significantly drop weed density and biomass, and reduce the competition effects between weeds and tea trees.(3) Covering Aquatic plants in the tea plantation could improve the growing and ecological conditions of tea garden and improve the quality and production of the tea. |
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