Spatial And Temporal Distribution And Flux Budget Of Dissolved Organic Carbon In Different Terrestrial Ecosystems

This thesis focused on carbon cycle in the terrestrial ecosystem,and aimed to estimate the fluxes of dissolved organic carbon(DOC)from land to aquatic systems in different terrestrial ecosystem types.The lateral transport of DOC plays an important role in linking carbon cycles of terrestrial and aquatic ecosystems.Neglecting the lateral flow of DOC can lead to an underestimate of the organic carbon budget in terrestrial ecosystems.It is thus necessary to integrate DOC concentrations and fluxes into carbon cycle models,particularly for the development of models that are intended to directly link terrestrial and ocean carbon cycles.To achieve this goal,however,more accurate information is needed to better understand and predict DOC dynamics.In this paper,the main contents include the collection of DOC from different terrestrial ecosystems at global scale,and building database of DOC from regional catchment in China,analyzing the relationship between export of DOC and climate factors,soil conditions and net primary productivity(NPP),and summarizing the differences of DOC studies under terrestrial ecosystems.The paper proposed the technical framework of DOC research in the regional catchment and in different terrestrial ecosystems at global scale,and used the proposed technical framework to quantify fluxes of DOC from the different terrestrial ecosystem and the three rivers in China,to determine the sources and driving factors of DOC in different terrestrial ecosystems.Finally,this paper describes in detail the important role of DOC played in terrestrial ecosystems.This study provides data support for the estimation of DOC export from land into the aquatic system in different terrestrial ecosystems and verification for the linking of ecological processes models of terrestrial and oceanic carbon cycle.Main results and conclusions are listed as follows.(1)Relationship between soil solution DOC concentration and environmental factors in different terrestrial ecosystems and budget of DOC fluxBased on the database of soil solution DOC from different terrestrial ecosystems,this paper mainly elaborates the vertical distribution of DOC concentration in different ecosystems,analyzes the correlation between DOC concentration and soil conditions and other environmental factors,and identifies the main factors influencing the export of DOC in forest ecosystem and wetland ecosystem.The empirical statistical model was established through analyzing the relationship between the DOC flux of soil solution and the environmental factors and soil conditions to analyze the global forest ecosystem and wetland ecosystem.The flux of DOC in boreal,temperate and tropical forest ecosystem was estimated to be about 18.4 Tg yr-1,15.5 Tg ?yr-1 and 30.4 Tg ?yr-1,respectively.The flux of DOC in wetland ecosystem was estimated to be about 21.1 Tg ?yr-1,respectively.(2)Spatial distribution of DOC concentration and flux from the Yellow RiverThe Yellow River is located in arid and semi-arid climate zone,thus regional temperate and precipitation play important roles in variation of DOC concentration.The export of DOC reduced because of high temperature,large evaporation and low precipitation induced by the regional climate.The result showed that mean annual efflux of DOC was 0.06 Tg yr-1,and the DOC concentration was 2.7±0.38 mg L-1 in the Yellow River.There was obvious seasonal variation of DOC in the Yellow River.(3)The relationship between flux of DOC and impact factors from the Yangtze RiverThe flux of DOC from the Yangtze River to ocean was 1.85 Tg yr-1,and the DOC concentration was 2.24 ± 0.53 mg L-1.There were obvious seasonal variations of DOC concentration.There was significant positive relationship between regional net primary productivity of vegetation and DOC concentration.As the Yangtze River is located in temperate and subtropical climate zones,which has appropriate temperature and abundant rainfall,it has higher net primary productivity.Regional net primary productivity of vegetation plays an important role in variation of DOC in the Yangtze River.(4)The export and impact factors of DOC from the Pearl RiverThe Pearl River is located in subtropical climate zone;therefore the temperature and rainfall are no longer limiting factors for DOC flux.There was significant positive correlation between regional annual NPP and DOC concentration in river.Results showed that regional NPP was an important factor on variations of DOC in river.The mean annual flux of DOC to ocean was 0.82 Tg yr-1,and the concentration of DOC was 1.51 ± 0.09 mg L-1.(5)Comparative analysis of DOC in the three main rivers in ChinaThe flux of DOC from the three rivers to ocean was about 2.73 Tg yr-1.There was a positive correlation between DOC flux and river discharge,and there was significant relationship between DOC concentration and net primary productivity of regional vegetation.The mean annual flux of DOC was the highest in the Yangtze River among the three rivers,followed by the Pearl River and the Yellow River.However,The DOC concentration was the highest in the Yellow River,followed by the Yangtze River and the Pearl River.As the three rivers are located in different climatic zones,DOC concentration and flux are significantly different.The DOC flux of the Yellow River was limited by low rainfall,high evaporation,and low vegetation coverage.The analysis on variations of DOC regional flux and concentration in rivers based on the geographic information system will improve overall understanding of DOC export from rivers in China.