Spatial And Temporal Variations Of Riverine CO₂ Outgassing Under Different Land Cover Types In The Yelllow River Source Region

Rivers connects the land and the ocean,acting as both container and pipe,continuously transporting carbon from terrestrial carbon pool to the ocean carbon pool.At the same time,the process has huge effect to carbon cycle of the other carbon pools within the basin.In the study,totally 36 representative samples of five different stream orders of the Yellow River and four land cover types,including glaciers,wetlands and grasslands were selected.Totally four times of sampling were conducted in April,June,August and October of 2016.Efflux of carbon dioxide?FCO₂?and pressure of carbon dioxide?pCO₂?were measured by Li-7000 analyzer.The river discharge,pH and DO?Dissolved Oxygen?were measured in site.Water sample were also collected in order to analyze DOC?Dissolved organic carbon?and the other environmental indicators.Combined with analysis of chemical parameters and environmental factors,various factors impacting p CO₂ and FCO₂,such as land cover type were discussed.The results show that the rivers in the source region of the Yellow River are the source of CO₂,the pCO₂ is between 441 and 2441?atm?average of 772±363?atm?and FCO₂ ranges from-221-6892 g C m^-2 yr^-1(average of 700±854 g C m^-2 yr^-1).The CO₂ emission from the rivers covered with peatland is the largest.The CO₂release from the rivers in glacier and permafrost regions is the least,and the FCO₂ of glacier is more than that in permafrost.The CO₂ outgassing from the rivers in grassland area is in the middle level.Because the high altitude and cold conditions limit the degradation of endogenous carbon,the fixation of exogenous organic carbon in terrestrial vegetation is the main source of riverine CO₂.This is the reason for the difference of riverine CO₂ emission under different land cover types.The main carbon source of FCO₂ in the is the erosion of soil by surface water.The controlling factor of FCO₂ in the Yellow River Source region is the physical erosion of the surface water.FCO₂ and pCO₂ showed significant seasonal changes in the same area,with the maximum occurring in August and followed by October,April,and June,which was mainly due to the growth cycle of plants growth and hydrology.Based on the four land cover types in glaciers,permafrost,grasslands and wetlands,this study has conducted in-depth discussions on river carbon emission and its mechanism in the Yellow River Source Region.It provides data foundation and technical support for the accurate measurement of global river carbon emission and the formulation of carbon emission policies.