| Wetland is the important component of terrestrial ecosystem.It is natural composition formed by the reciprocity between lake and land,and is of great significance for the surviving and development of biont.In the context of climate change and intensifying human activities,that studying the eco-hydrological process is significant for the preservation and restoration of wetlands,and has been a hot issue in the world.Poyang Lake is the largest freshwater lake and internationally important wetland.In recent years,with the effect of intensifying human activities,Poyang Lake suffers from some troubles,such as the earlier appearing of low water level in Poyang Lake and lasting longer than before,wetland degradation and sharp decline in biodiversity.This has been brought into public focus,and it is essential to study the eco-hydrological processes at Poyang Lake wetland for its sustainability.The thesis uses stable isotope techniques and computer model to study the eco-hydrological processes at Poyang Lake wetland.The main work and conclusions are as follows:(1)Stable hydrogen and oxygen isotope techniques are used to study the hydrological cycle at Poyang Lake wetland.A significant liner relationship between ?D and ?18O of the water samples,including rain water,soil water,groundwater,river water and plant stem water at different growth stages.The slope and interception increase with plant growth rhythm.During dry period,the groundwater can recharge deep soil water,even surface soil water by two ways.Firstly,the groundwater can rise through capillary rising.Secondly,the water vapor diffusion from groundwater also can recharge soil water.When recharging soil water,groundwater also can recharge river during dry period.Rain water recharges soil water in the form of piston flow.During wet period,with the rainfall increasing the water table increases and is exposed in the air.In the meantime,the Poyang Lake level also increases,but lower than water table.Water movement in soil can affect the water use patterns of wetland herbaceous plant species in different seasons.During the rainy season rain water is the main water source,while during the rainy season the plants use a combination of rain water,surface soil water,deep soil water,and groundwater.During extremely dry seasons,deep soil water and groundwater may be the main water sources.However,irrespective of the season,herbaceous plant species preferentially uses rain water,which can effectively recharge surface soil water by rain water.(2)Stable carbon isotope technique is used to study the carbon cycle in plant and soil at Poyang Lake wetland.Plant foliar 813C in dry period is significantly larger than that in wet period.In different seasons,there is significant variation in foliar 513C between C3 and C4 plants,and among C3 or C4 plants,the variation is also significant.Except for C4 plants and C3 emergent plant,the 813C and water use efficiency of Carex cinerascens are significantly larger than that of other C3 plants in wet season,while ?13C and water use efficiency of Phalaris arundinacea are significantly larger than that of C3 plants in dry season.The wetland plant foliar 813C varies with environmental factors(temperature,water availability and nutrition).Different from other researches,the foliar ?13C and water use efficiency of C4 plants decrease with the water availability increasing.The ?13C of soil organic carbon is characterized by spatial and temporal variations,and is affected by the relative abundance of C3 and C4 plants.The spatial variation of proportions can be used to study the relative abundance of C3 or C4 plants in different regions in certain season,while the temporal variation can be used to study the succession of C3 or C4 plants during different growing seasons in certain region.(3)Stable nitrogen isotope technique is used to study the nitrogen cycle in plant and soil at Poyang Lake wetland.In different seasons,the foliar 815N of most C3 plants are larger than that of C4 plants.during different seasons,the foliar ?15N in dry seasons are significantly larger that in wet seasons.There is no apparent relationship between ?15N and ?13C in wetland plants,while a significantly negative correlation between ?15N and 813C is observed in soil.The environmental factors can't influence the wetland plant ?15N,while it is opposite for soil 815N.In the meantime,the significant correlation is observed between ?15N of soil and that of foliar.This indicates that environmental factor influence plant nitrogen cycle through the soil nitrogen cycle.(4)Eco-hydrology model for typical section is developed.The thesis develops an Eco-hydrology model for typical section at Poyang Lake wetland.The experimental results can reflect the mechanisms of Eco-hydrological process. |
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