The Source,Composition And Control Factors Of Dissolved Organic Matter Of The Three Gorges Reservoir

Rivers transport large amounts of organic carbon from land to ocean,which is an important part of the global carbon cycle.The construction of dams all over the world has changed the hydrological environment and hydrodynamic conditions of rivers,including making the river fragmentation,changing the production mode of the ecosystem from heterotrophy to autotrophic gradually,and increasing the residence time of water.These changes interfere with the role of rivers in the carbon cycle,forming a"reservoir effect".Dissolved organic matter(DOM)is the main pool of organic carbon in aquatic ecosystems.Its characteristics and changes profoundly affect the balance of river ecosystems.Therefore,studying the source and transformation of DOM in the reservoir area is of great significance for exploring the carbon cycle of drainage basins affected by dams.This thesis selects the main stream and typical tributaries of the world's largest reservoir-the Three Gorges Reservoir(TGR),and evaluated the impact of reservoir drainage and storage on the DOM chemistry in the mainstream and tributaries of the TGR.We used total stable carbon isotope,optical spectroscopy and high-resolution mass spectrometry to preliminarily explore the impact of DOM properties of the mainstream and tributaries of TGR during drainage and storage periods.The main knowledge gained is as follows:1.The source characteristics of 28 DOM samples in tributaries during water storage and drainage periods were assessed,and the proportion of different sources was semi-quantitatively using PARAFAC analysis.The bottom water DOM of the drainage period was mainly from autochthonous sources,reaching 58.4±10.3%,The average Aromaticity Index(AI_mod)of SPE-DOM during the drainage period was 0.27.During the storage period,the surface and bottom water DOM were mainly allochthonous,and the surface DOM of allochthonous sources during the storage period reached59.7±9.9%.Meanwhile,the relative proportion of highly unsaturated compounds reached 88%,which are mainly from allochthonous sources.2.Similar to tributaries,PARAFAC semi-quantitatively assessed the proportions of 32 DOM samples from different sources of the mainstream during storage and drainage periods.During the drainage period,both the autochthonous and allochthonous sources of DOM at the bottom or the surface were about 50.0%,while the DOM of the storage period showed a signature with more obvious allochthonous sources.The allochthonous DOM at the surface of the storage period reached59.7±9.9%,and the average molecular weight of SPE-DOM was large,reaching 470Da.3.The comprehensive evaluation of 60 DOM samples in the drainage and storage periods in the study area found that the source of the DOM was significantly different during the drainage and storage periods.The autochthonous signal of the DOM in the drainage period was obvious,while the autochthonous and allochthonous sources in the storage period were similar.Combining the background of regional algae blooming,water level changes,hydrodynamic changes,the influence of water discharge on tributary DOM proposed by previous studies,and the results of PCA analysis in this study,we suggested that the difference in DOM of the tributary during the storage period was mainly due to the algae blooming and the changes in hydrodynamic mode.The difference in the main stream DOM was mainly due to the retention time of the water body caused by the water discharge of the TGR.However,due to the complex mechanism in the reservoir area,such as the main stream was affected by the lateral input of the tributary,and the tributary was also affected by the density current of the main),the specific constraining factors need to be further studied.