| hTeh ew awtaetre-rl-elveevle-lf-lfulcutcutautaitnign gz oznoen er erfeefresr ts ot oa tar tarnasnitsiitoino ne ceocloolgoigciacla la raerae aw whehreer er erseesrevroviorisr,s,are flooded or exposed to land due to the periodical fluctuation of water level,and the area formed between the highest water level line and the lowest water level line.The Danjiangkou reservoir,as the water source of the South-to-North Water transfer Project,which is particularly important for the sustainable development of economy and society and ensures the water quality and quantity in the source area.The vegetation of the reservoir bank of water-level-fluctuating zone is the last ecological barrier to intercept,prevent and control the entry of pollutants into the receiving water,which plays an important ecological role in purifying sediment and pollutants carried by surface runoff.In this study,Danjiangkou reservoir was selected as the researched object.Based on field surveys,the dominant species of bermudagrass and Alternanthera philoxeroides were selected as experimental materials,and three treatments,blank bare ground,Cynodon dactylon vegetation filter belt and Alternanthera philoxeroides filter belt,were set up.Through the indoor pool simulation Danjiangkou hydrological rhythm changes,set every4d ups and downs,each fluctuation 15cm,thus forming four different water level areas in the soil tank,these four areas were named A,B,C,D.Experiments were conducted to investigate the effects of different vegetation filter belts on the purification of sediment,total nitrogen,ammonium nitrogen,total phosphorus,and soluble phosphorus in runoff through flooding experiments,and the effects of vegetation-hydrology on soil total nitrogen and ammonium nitrogen in vegetation belts.,Nitrate nitrogen,total phosphorus,available phosphorus changes.(1)Vegetation filter belt can effectively delay the generation of initial runoff,reduce the peak value of the slope runoff,and increase the infiltration of slope flow.Compared with the blank bare land,the vegetation filter belt adds 2.3L of slope water per minute,the contribution rate of vegetation reached about 40%.The runoff interception rate,retention rate and flushing time of the three treatments showed a significant exponential function(y(28)ax~b).(2)The vegetation filter belt can effectively retain sediment,nitrogen,and phosphorus of runoff.In the early stage of water release,the interception rate of two vegetation filter belts was more than 85%.There is a significant negative linear correlation between sediment rejection and runoff time.The detoxification rates of total nitrogen,ammonium nitrogen,total phosphorus and dissolved phosphorus in the Cynodon dactylon filter belts were 23%,11%,10%and 12%,respectively.The Alternanthera philoxeroides filter belt was used for total nitrogen,ammonium nitrogen,and total nitrogen.Phosphorus and soluble phosphorus balance were 20%,14%,15%,and 18%respectively.(3)The growth of the two kinds of plants was seriously disturbed by hydrology.Flooding had an inhibitory effect on the growth of Cynodon dactylon,and proper flooding had a positive effect on the growth of Alternanthera philoxeroides.After the entire water level change period,the survival rates of Cynodon dactylon treatment areas A,B,C,and D were 0.0,0.25,0.75,and 0.85,respectively.There were different degrees of greening of Cynodon dactylon in areas B and C.The plant height and total growth rate of Alternanthera philoxeroides in the four regions showed a significant positive linear correlation with the hydrological change time.(4)The results of vegetation-hydrological conditions on soil N and P indicated that the vegetation-hydrological conditions mainly affect the content of available N and available P in soil,and have little effect on the content of total N and total P in soil.After removing the pollutants from the runoff with the vegetation filter belt,the water level rising after 12-16d more effectively prevents the nitrogen and phosphorus pollution from entering the water,and achieves more scientific use of the vegetation filter belt to control agricultural non-point source pollution.Before the two vegetation treatments in the C area,the nitrate nitrogen,ammonium nitrogen,and total phosphorus in the soil reached an equilibrium state before the flooding(12 days),indicating that the vegetation can effectively reduce the nitrate in the soil after 12 days of absorption and transformation.Before the flooding in the D area(16 d),the soil total nitrogen reached an equilibrium state,indicating that the vegetation can effectively reduce the total nitrogen in the soil into the water after 16 days of absorption and transformation.(5)The presence of vegetation filter bands enhances the adsorption and fixation of nitrogen and phosphorus in the soil.Changes in water levels seriously affect the release of nitrogen and phosphorus from the soil.The results of soil nitrogen and phosphorus retention and release indicated that the total nitrogen and phosphorus retained in the soils of the two vegetation treatments were significantly higher than that of bare soil.There was no significant difference in total nitrogen and phosphorus retained in the soil between two vegetation treatments,indicating that the presence of vegetation filter bands enhances the adsorption and fixation of nitrogen and phosphorus in the soil.However,there was no significant difference in the adsorption and fixation capacity of soil nitrogen and phosphorus between two vegetation filter belts.Compared with the treatment of bare land,the amount of total soil nitrogen released in the A,B,C,and D areas of Bermudagrass treatment was 1/4,1.00,1.47,and 1.93 times higher than that of the bare ground treatment.The amount of soil total nitrogen released in A,B,C,and D areas of Alternanthera philoxeroides was 3.94,3.08,1.64,and 1.77 folds higher than that of blank bare soil treatment.(6)There was a significant linear positive correlation between total nitrogen and total phosphorus retention and release of three treatments,indicating that the more nitrogen and phosphorus in the runoff,the greater the release of soil.The amount of total nitrogen in the three types of treated soil was higher than that in the soil under hydrological change.The total soil phosphorus released from the bare ground and the soil treated with Alternanthera philoxeroides was higher than the total phosphorus released from the runoff soil.The total phosphorus released from each area of Cynodon dactylon treatment was lower than that of the soil that was trapped in the soil. |
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