Temporal And Spatial Characteristics Of Carbon Emission And Carbon Transport In The Middle Reaches Of The Yellow River

As the link between soil,atmosphere and ocean,rivers play a vital role in the global carbon cycle.This paper selects the middle reaches of the Yellow River as the research area,taking the Toudaoguai Hydrological Station in Inner Mongolia and the Tongguan Hydrological Station in Shaanxi as the monitoring sites,Based on the continuous monitoring data from 2011 to 2019,analyze the temporal and spatial variation of environmental factors,DIC,DOC,pCO₂ and FCO₂,carry out correlation analysis of environmental factors with carbon concentration and carbon emission,and clarify the impact of environmental factors on carbon transport and carbon emission.The main results are as follows:（1）The DIC concentration in the middle reaches of the Yellow River was generally between 4.50 and 34.83 mg/L,with obvious seasonal differences,higher in winter and lower in summer,The DIC concentration at the upstream Toudaoguai station（22.55 mg/L）was higher than that at the downstream Tongguan station（19.18 mg/L）.The change of flow and the inflow of chemical weathering products were the main factors leading to the spatial difference of DIC;The overall DOC concentration was between 1.17 and 12.97 mg/L,and the upstream Toudaoguai Station（5.78mg/L）was slightly higher than the downstream Tongguan Station（5.3mg/L）.The seasonal differences showed that it was higher in summer and lower in winter.Concentration changes are mainly affected by human activities.（2）The overall pCO₂ in the middle reaches of the Yellow River is between 40 and 24087μatm,and the seasonal trend is winter>spring>summer>autumn.The pCO₂ of the downstream Tongguan station（2606μatm）was higher than the upstream Toudaoguai station（1973μatm）,The chemical weathering of carbonate-rich soils in the Loess Plateau is the main reason for the high pCO₂ in the middle reaches;The overall FCO₂ranged from 0 to 2307 mmol/m~2/d,and the seasonal performance was the highest in summer and the lowest in winter.The FCO₂（296 mmol/m~2/d）of the downstream Tongguan station was higher than the upstream Toudaoguai station（200 mmol/m~2/d）,and the differences in flow rate and pCO₂ were the main factors leading to the differences in the spatial distribution of FCO₂.（3）River carbon concentration（DIC and DOC）is mainly affected by TSS,water temperature,flow,p H,alkalinity,etc.There was a significant negative correlation between DIC and DOC at Toudaoguai Station（R~2=0.0420,P<0.05）,indicating that the organic carbon in the river mainly came from endogenous sources.There was a significant positive correlation between DIC and DOC at Tongguan Station（R~2=0.3869,P<0.01）,indicating that both were affected by exogenous carbon input;Carbon emission is mainly affected by flow rate,water temperature and flow.The increase of carbon concentration will promote the increase of photosynthesis of aquatic plants and algae,which will lead to the decrease of pCO₂ and FCO₂.