| As a key water source of North Water Transfer Project and first level water source protection areas of national State, Danjiangkou Reservoir will provide drinking and production water to Henan、Hebei、Beijing、Tianjin four provinces and more than20cities, So water safety and environmental protection is extremely important. And Affected by agricultural economy and people’s production and living activities in the Water source areas, Danjiangkou reservoir bank carrying a huge load of pollutants which come from the upper farmland every year. Including pesticides, fertilizers and sediment concentration which washed down with runoff also can’t be ignored. If let them free directly into the water, will increase the burden of water pollution, and water security will be seriously threatened.Reservoir bank vegetation buffer zone is an effective means to trapping Land-point source pollutants and improving the water quality of the reservoir. Therefore, conducting a systematic investigation on existing Reservoir bank and buildding a suitable buffer zone to make it has best ecological benefits of intercepting sediment and nitrogen and phosphorus retention. Protect water safety has become the most urgent task of ecological environment construction and protection in Danjiangkou Reservoir.In this paper, using three kinds of typical reservoir bank vegetation buffer zone to carry out field simulated runoff erosion experiments. Through a combination of outdoor testing and indoor measurement and analysis to study the buffer zone’s capability of purifying pollutants came from land-based sources. From the soil, vegetation type, runoff flow, pollution load and buffer width perspectives to explore the mechanism of reservoir bank vegetation buffer zone purify agricultural nonpoint source pollution. The main conclusions are as follows:1. There is a negative linear correlation between initial soil moisture and runoff time in each vegetation buffer zone, and the correlation coefficient vary between0.694and0.976, which indicating that the higher the initial soil moisture, the shorter the time of simulated runoff; In addition, with the increased runoff flows, the value of K which representing the slope of the fitted line becomes smaller, directing that the effects of the initial soil moisture on the runoff time reduced while the runoff flows increased.2. On the whole, undering the condition of different runoff flows and nutrient concentrations, the average removal rate of different types of vegetation buffer zones for SS、NH4+、NO3-、TN、TP and SRP is90.4%.77.4%、9.6%、16.9%.55.3%and44.1%respectively. Obviously, their depuration effects on SS、NH4+、TP、SRP、TN and NO3-increase successively.3. The depuration effect of vegetation buffer zones for SS descends between Imperata、Bermudagrass and Locust. The experiments show that vegetations play a vital role on trapping sediment in runoff of buffer zones, especially those herd which is hard and bushy, furthermore, the trapping capacity for sediment of the herbal buffer zone is stronger than the tree buffer zone.4. Comprehensively, with the increase of pollution loading, various kinds of riparian vegetated buffer have a decrease trend of purifying rate to NO3-, TP and SRP, but an opposite trend to TN, and in the Bermuda grass and acacia buffer strips, the purification rate to NH4+shows an increasing at first and then reducing trend, with the increase of pollution load.5. Under different conditions of water flow rate, the vegetated buffer strips have different purification rate to pollutants. Generally speaking, with the increase of flow rate, the vegetated buffer zone under different conditions of pollution load showed a declining trend to the purification rate of NH4+, NO3-,TN, TP and SRP.6. According to the experiments, there are certain differences among concentration of the pollutants in surface runoff and interflow, and the concentration of the pollutants in interflow is lower than that in surface runoff. The average concentration of NH4+、NO3-、 TN、TP、and SRP account for66.9%、95.1%、95.8%、93.7and88.9%of the surface runoff after balance respectively. Interflow has purification to pollutants through vertical migration and lateral transfer in the process of infiltration, which is limited.7. In the stable phase, the average runoff flow is109.8ml/s and29.3ml/s with a flow of0.2L/S washout to the Bermuda grass buffer zone, which has a difference of3.75 times. As the interflow lasts a long time, it comes a result that the total amount of surface runoff and interflow are183.87L and107.44L, respectively. And the surface runoff flow is only1.71times of the interflow. It can be calculated that the amount of output of pollutants (NH4+、NO3-、IN、TP、and SRP) are40.74mg、1392.50mg.1353.21mg、51.01mg and25.05mg, which account for10.3%.70.5%.67.7%、23.5%and60.0%of total input, respectively.8. The results of Correlation analysis between various pollutants show that the SS content and TP content have a significant positive relationship with the correlation coefficient of0.469, except that various forms of N, P have significant relationships, respectively. And NH4+content have significant positive relationships with TP and SRP, with the correlation coefficient of0.324and0.644, respectively. In addition, NO3-and SRP have a significant positive relationship, with the correlation coefficient of0.469.9. Introduction of adsorbed phosphorus (SP), and use SPSS to do correlation analysis between SP and runoff sediment concentration. The results showed that there was a significant positive correlation between the SS and the SP content, correlation coefficient was0.703, almost twice the correlation coefficient of SS and TP content (0.348). Therefore, It can be inferred that the reason why SS and TP showing highly significant correlation is mainly because of SP, and as SS is increased,showing a linear growth trend. |
PDF Full Text Request