Dynamic Pattern of Riverine Carbon Concentration and Its Isotopic Character
Supervisor:zhang quan fa
Carbon(C)in riverine ecosystems plays an important role in regulating terrestrial carbon reservoir to the oceans and atmosphere,thus,understanding C dynamics in riverine ecosystem is essential for understanding global carbon cycle.The effects of anthropological factor on riverine C cycle are increasingly critical under the background of global change.As an important component of global change,land use and land cover change greatly effects the structure and function of riverine ecosystem.But the influence mechanism of land use and land cover change on spatial and temporal variations of riverine C with their sources,transport,transform and interactions remains unclear.Thus,we conducted experiments in the Upper Han River basin to explore the character of spatial and temporal variations of riverine C input,including dissolved inorganic carbon(DIC),dissolved organic carbon(DOC),total suspended solid(TSS),particulate organic carbon(POC),and trace riverine C sources by using C stable isotope methods.The main conclusions are as follows:(1)Seasonal variations significantly affected riverine C concentrations and their stable isotope signature.Seasonal variation of riverine environmental factor was significantly different in the upper Han River tributaries.pH was significantly lower in rain season than dry season,NO3--N、NH4+-N and TSS concentrations were significantly higher in rain season than dry season.Water temperature and turbidity were significantly positive related to NO3--N、NH4+-N and TSS concentrations,river nutrient was closely relative with human activities.On the spatial scale,81 percentage of river water quality was healthy,but riverine nutrient concentrations were relatively higher in Yue River,Ba River and Xun River,human activeties were heavily effect in these palce.(2)Seasonal and spatial variations significantly affected riverine C concentrations and their stable isotope signature.Seasonal variation of riverine C concentrations and their stable isotope signature was significantly different.DIC concentration was significantly higher in summer and rain season than other seasons.POC concentration was significantly higher in summer and winter.δ13C-DIC was significantly higher in winter and dry season.δ13C-POC was significantly lower in winter,but did not show significantly different in rain and dry season.Based on the relationship of DIC and POC with other water variables,higher temperature evaporation increased riverine DIC and POC concentrations in summer,heavy rainfall increased allochthonous riverine DIC and POC concentrations input in rain season;Lower temperature and TSS concentration in winter probably benefit to riverine aquatic photosynthesis,it increased riverine δ13C-DIC and contributed more autochthonous riverine POC.also reduced riverine δ13C-POC.The difference between main channel and tributaries significantly affected riverine POC concentration and δ13C-POC signature,but it not significantly affected riverine DIC concentration and δ13C-DIC signature.Riverine POC concentration located in main channel was significantly higher than tributaries in rain season,δ13C-POC value located in main channel was significantly lower tha tributaries in dry season.Incrased water discharge in rain season probably resulted in higher POC concentration in main channel.Compared with tributaries,stable river circumstance in main channel was advantaged to increased contribution of autochthonous POC in dry season,also reduced riverine δ13C-POC.TSS was the primary influence factor of DIC isotope signature variation,DIC was the primary influence factor of POC isotope signature variation.(3)Land use types significantly affected riverine C concentrations and their stable isotope signature.Land use types significantly affected riverine DIC and POC concentrations with their stable isotope signature.Riverine DIC concentration input was significantly increased in cropland and urban land,riverine POC concentration input was significantly increased in cropland,urban land and bare land.δ13C-DIC value was significantly lower in bare land.Based on the relationship of DIC and POC with their source,agricultural fertilization may be primary reason of increased DIC and POC concentrations input in cropland;The higher contribution of silicate weathering in bare land than other land use types,resulting in lower δ13C-DIC in bare land.Soil organic matter erosion was happed in bare land because lack of vegetation cover,caused higher riverine POC concentration in bare land.Anthropogenic emission increased riverine DIC and POC concentrations input in urban land,city organic pollution probably enriched the isotope signature of riverine POC,changed the difference between urban land and other land use types.In addition,our results showed that riverine C input was possibly affected by allochthonous riverine carbon.The contributions of aquatic photosynthesis and autochthonous organic C were significantly increased in winter and dry season.Anthropogenic activity resulted in extra C input to river in cropland,urban and bare land,the composition of δ13C-DIC and δ13C-POC was significantly changed in bare land and urban,respectively.DIC fertilization effect on aquatic photosynthesis connected riverine inorganic C with organic C.