| Based on the urban forest ecological station of Yangtze River Delta,the processes of water cycle of canopy interception,stem-flow,surface runoff,soil infiltration,evapotranspiration and so on were studied by means of quantitative positioning in 2016.In this paper,the mechanism of water transport and transformation in the process of water cycle of Oka forest on Kongqing Mountain was studied.The water balance equation was used to analyze the water conservation status of Oka forest.The study provides a theoretical basis for the evaluation of forest water conservation.The results are as follows:(1)The total annual rainfall in the study area was 1876.2mm.Rainfall mainly concentrated in the summer and autumn accounting for 75.4% and July was the highest(380.4mm),the lowest in February(25.1mm).Duration of rainfall in Oak forest was delayed from 0.01 h to 3.57 h,1.15 h on average.The regression model on the relationship between rainfall duration and rainfall: P = 21.316 D + 42.654,R2 = 0.8618.(2)The correlation between precipitation and rainfall was excellent with the regression model: T=0.7732P+0.5792,R2=0.9939;the regression model on the relationship between stem-flow and rainfall: S=0.032P-0.12.02,R2=0.9589;the regression model on the relationship between stem-flow and rainfall intensity: S=1.5775Q+5.1925,R2=0.8355;the regression model on the relationship between canopy interception and rainfall: I=13.045ln(P)-41.366,R2=0.9057;the regression model on the relationship between canopy interception and rainfall intensity: I =-3.9294Q2+4.8324Q+19.598,R2=0.8041;the regression model on the relationship between canopy interception and Leaf area index: I=0.5192L2+1.5585L-0.0919,R2=0.8882;the regression model on the relationship between canopy interception related factors: I=-0.376+0.974P-0.96S-0.968T-0.069 Q,R2=0.998.(3)The water content of litter layer reached the peak(35.39%)in July,and reached trough(24.16%)in September.The water content of litter layer was on the rise from January to July,which in the period from July to September showed a decreasing trend and began to rise again from September to December.(4)There were only 3 rainfall runoffs in the measurement period.The peak value of soil moisture in each layer appeared in July.Comparison of soil water content in each layer: 0~10cm layer >20~40cm layer >60~100cm layer >10~20cm layer >40~60cm layer.The initial infiltration rate of soil was very high while the average infiltration rate was 8.52mm/min.Comparison of infiltration rate: May > June > July.(5)The sap flow showed a single peak circle in the days,reaching the peak at noon.The simulation results of Rithchie and Zhang et al.’s models have good effect on the annual variation trend of evapotranspiration,but in general,the simulation results of the Rithchie’s model on the monthly dynamic and total amount of evapotranspiration in Oka forest are not as good as the Zhang et al.’s model.The correlation between the actual evapotranspiration and temperature,soil temperature,air pressure,soil moisture and rainfall was significant,but not significant with wind direction,wind speed and relative humidity.(6)In Oak forest ecosystem water cycle process,66.43% of the rainfall through the canopy;3.11% rainfall as stemflow form run into the soil;interception accounted for 30.45% of rainfall;runoff accounted for 0.09% of rainfall;46.05% of rainfall lost way by evaporation.The total increment of water conservation in oak forest ecosystem was 439.31 mm,accounting for 23.42% of the total rainfall in 2016.The increment of water conservation was highest In October(128.92mm)while the highest loss was in March(-16.03mm). |
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