Water Balance Process Analysis Of Rubber Plantation Ecosystem In Danzhou,Hainan Island

Rubber plantation ecosystem is one of the most important forest ecosystems in the tropics,and it is also an important tropical cash crop.It is of great significance to explore the water balance process and eco-hydrological effect of rubber forest.Using the surface layer observation system and the water balance observation site in the third test area of Rubber Research Institute,Chinese Academy of Tropical Agricultural Sciences,this paper revealed the change of evapotranspiration and water vapor flux in rubber forest ecosystem through the positioning observation in the three years from 2017 to 2019.The response of evapotranspiration to various environmental factors was also analyzed based on meteorological data.The distribution characteristics and closure levels of water balance components such as rainfall,surface runoff,canopy interception,soil storage,soil leakage and evapotranspiration in this rubber forest ecosystem were systematically analyzed.The distribution of rainfall by rubber canopy was studied,and the hydrologic processes and functions of water balance of each component were sorted out.The errors of the two methods are analyzed by comparing the evapotranspiration of rubber forest obtained by water balance method and vorticity correlation method.The results are as follows:(1)Characteristics of precipitation and evapotranspiration in the rubber forestThe total annual rainfall in 2017,2018 and 2019 was 1687.6mm,2264.7mm and 2222.9mm,respectively.The total evapotranspiration was 962.24 mm,1209.29 mm and 1232.05 mm,accounting respectively for 57.02%,53.40% and 55.43% of the rainfall.The average annual rainfall in the three years was 2,058.33 mm and the average annual evapotranspiration was 1,134.53 mm,accounting for 55.12% of the precipitation.The evapotranspiration level of rubber forest is higher than that of most subtropical artificial forests,but it is similar to that of tropical rain forest in similar latitudes,which indicates that the evapotranspiration level of rubber forest belongs to the reasonable range of forest ecosystem evapotranspiration.(2)The variation characteristics of water balance componentsDuring the observation period,the through fall was 1606 mm,accounting for 74.2% of the rainfall;the stem flow was 241.6mm,accounting for 11.2% of the rainfall in the same period;the canopy interception was 308 mm,accounting for 14.6% of the rainfall in the same period;the total annual surface runoff was 152.8mm,accounting for 6.87% of the annual rainfall.It shows that in the rubber forest,the main component of water distribution in the rainy season is through rain,which is the main source of soil water supply.In the secondary distribution of rainfall,soil water storage was the highest,surface runoff was 152.8mm,accounting for 6.9% of the rainfall,and soil leakage was 491.2mm,accounting for 22.1% of the total rainfall.(3)General characteristics of water balanceIn 2019,the water budget of the ecosystem of Hainan Danzhou rubber forest is basically in balance on the annual scale,and the water input,that is rainfall,is 2222.9mm.The amount of water output was divided into evapotranspiration,surface runoff and soil leakage.The total amount was 1876.05 mm,and the income was greater than the total amount of expenditure.According to the comprehensive data of three years,the average evapotranspiration in the rainy season is 913.91 mm,which is less than the rainfall of 1818.87 mm in the same period.In the dry season,the evapotranspiration is equal to or slightly higher than the rainfall,which indicates that the rainfall during the rainy season can guarantee the water supply for the normal growth of the rubber forest,but when the rainfall is insufficient in the dry season,external water supplement is needed to ensure the normal growth of the rubber forest.(4)Effects of meteorological factors on water balanceThe influence of meteorological factors on water balance mainly affects the two processes of evapotranspiration and soil leakage.For the water lost to the atmosphere,which is the evapotranspiration process,it is mainly affected by net radiation,atmospheric temperature and saturated vapor pressure difference,and is positively correlated.For soil layer water loss,that is,groundwater leakage,is mainly affected by atmospheric pressure and rainfall,but the action time is in a few hours or days,on an annual scale there is no obvious effect.However,the surface runoff is mainly affected by rainfall intensity,rainfall amount and canopy density,and is barely not directly affected by meteorological factors.(5)Comparison of the results of two measurements of evapotranspirationThe total amount of evapotranspiration calculated based on water balance method is 976.3mm,and the result of eddy covariance method within the same time is 958.72 mm,which is slightly lower than the calculation result of water balance method.However,the correlation between the two results is good and the evapotranspiration results can be both measured accurately.Both of them have some causes of errors,such as meteorological factors,surface layer turbulence interference,imperfect calculation model,and so on.This study investigated the water balance characteristics,water vapor exchange process and response to environmental factors of rubber forest ecosystem under different environmental conditions.It is of great significance to deeply understand the hydrological process and function of the rubber forest ecosystem,to reveal the response mechanism of the water in the rubber forest ecosystem to climate change,and to better cultivate the rubber forest and improve the yield of rubber at the same time to protect the eco-hydrological environment in the rubber plantation area.