Study On Water-Controlled Ecohydrological Processes

The link and interaction between hydrological and ecological processes are the key problem of ecohydrology.To rationally develop and utilize water resources and ecosystem natural resources should be based on the understanding of this problem.Also,it is the foundation of ecological protection and restoration as well as the realization of sustainable development.Water is one of the main drivers of ecohydrological processes which develop mostly under water-controlled conditions.In this thesis,a study is conducted on water-controlled ecohydrological processes.The mechanism of how climate change influences ecohydrological processes is discussed.Through data collection,the ecohydrological optimality theory is firstly validated and applied in Horqin Sands in the middle of the Northeast China Transect(NECT).The results show that this theory can be conducted in this area very well with proper chosen parameter values.The difference between theoretical vegetation cover and observed one is mainly attributed to the effect of non-growing season water residue.Specific mathematical relationships between vegetation cover and vegetation morphological character,vegetation cover and climate factors are found through the application of the theory.Secondly,by describing total rainfall with rainfall property parameters,mathematical analyses are executed to detect the effects of rainfall properties on vegetation cover.The trend of vegetation cover to total rainfall,or rainfall intensity,is positive.With growing rainfall frequency,vegetation cover increases first and goes down after a peak.Longer non-growing season length makes vegetation cover more sensitive to parameters related to non-growing season water residue.A discussion that different transpiration potentials of plant types affect vegetation cover is also given.It is suggested that plants with different transpiration potential may adjust vegetation cover to adapt to rainfall pattern changes on different levels.Furthermore,the direct and indirect causes of water balance change by rainfall can be distinguished through substituting the mathematical relationship between vegetation cover and rainfall properties into the water balance equation,and then using attribution analysis approach.Thirdly,a nutrient cycle model of carbon and nitrogen in the soil-plant system is coupled with the stochastic soil moisture model in this thesis.The effect of water to plant growth is viewed from a water-controlled plant nutrient cycle perspective.By the means of stochastic process theory and statistic approach,significant correlation is found between the mass in each carbon or nitrogen pool with others in the soil-plant system.Rainfall variation influences the mass in carbon and nitrogen pools through changing soil moisture.With increasing rainfall,plant carbon and nitrogen pool and soil carbon pool grow.While Soil organic total nitrogen pool and dissolved inorganic nitrogen pool shrink.Finally,a comprehensive application of the theory and models of water control on vegetation cover and nutrient cycle is conducted to analyze how the key ecohydrological processes develop in future climate scenarios in NECT.The results show:(1)vegetation cover increases without considering the transpiration potential change with climate.If taking the change of transpiration potential with climate into account,vegetation cover changes little in future climate scenarios.(2)According to the rainfall scenarios in the future,all mass in soil-plant system carbon and nitrogen pools reach new steady states in 2070,except for soil total carbon.