Analysis On The Influencing Mechanisms Of Greenhouse Gas Emissions From River Systems On The Loess Plateau

The global water body transmits a lot of greenhouse gases to the atmospheric environment every year,and the inland water body is an important part of the global water body.Rivers are an important link between marine and terrestrial carbon pools.In recent years,the release of greenhouse gases from inland water has attracted widespread attention.It is great significant for a comprehensive understanding of the global carbon cycle process by research the exchange flux of CO₂ and CH₄ for inland water bodies in arid/semi-arid regions.In this paper,the research objects are Kuye River and its representative reservoir.In July and October 2018,March and June2019,high-frequency observations of CO₂ partial pressure(pCO₂),CH₄ concentration and water-air interface CO₂ and CH₄ exchange fluxes(FCO₂,FCH₄)were carried out by using LI-7000 CO₂ analyzer and GC-2030 meteorological chromatography,By analyzing its temporal and spatial changes,expound the influence mechanism of environmental factors on carbon emissions and carbon concentration in water bodies.The main results and conclusions of the study are as follows:(1)The pCO₂ and FCO₂ of the Kuye River basin illustrate obvious temporal and spatial variation characteristics.The river index of pCO₂ and FCO₂(996?atm and94.5 mmol m^-2 d^-1,respectively)are higher than those of the reservoir(752?atm and10.3 mmol m^-2 d^-1,respectively).The seasonal difference of FCO₂ is obvious:for rivers,it is the highest in autumn(165.7 mmol m^-2 d^-1)and the lowest in spring(42.9mmol m^-2d^-1),while for reservoirs,it is the opposite,which showing the highest value in spring(16.6 mmol m^-2 d^-1)and the lowest in autumn(-5.4 mmol m^-2 d^-1).Spatially,the river FCO₂(114.8 mmol m^-2 d^-1)in the upstream sandy hilly region is about 30%higher than that in the middle and lower reaches of the loess basin(75.2mmol m^-2 d^-1),but for the reservoir,the reservoir FCO₂(16.4 mmol m^-2 d^-1)in the loess hilly region is significantly higher than that in the upstream sandy hilly region(1.2 mmol m^-2 d^-1).(2)There was noteble difference between CH₄ and CO₂.The concentration of CH₄ and FCH₄ in river water(0.24?mol L^-1 and 0.25 mmol m^-2 d^-1)were lower than those in reservoir(0.43?mol L^-1 and 0.74 mmol m^-2 d^-1,respectively).Seasonally,the FCH₄ of river water was the highest in June(0.75 mmol m^-2 d^-1)and the lowest in July(0.04 mmol m^-2 d^-1),and the FCH₄ of reservoir water was the highest in June(0.93 mmol m^-2 d^-1)and the lowest in March(0.003 mmol m^-2 d^-1).Spatially,the FCH₄ of the river in the loess hilly region(0.34 mmol m^-2 d^-1)is higher than that in the sandy hilly region(0.28 mmol m^-2 d^-1),and for the reservoir,the reservoir FCH₄(0.47 mmol m^-2 d^-1)in the sandy hilly region is significantly higher than that of the reservoir FCH₄(0.03 mmol m^-2 d^-1)in the loess hilly region.(3)The pCO₂ of watershed water is mainly affected by carbonate system,in which the carbonate buffering effect formed by high p H has the greatest influence on the morphology of DIC,so p H is the key factor to control pCO₂,followed by organic carbon decomposition,and velocity is the key factor to control the CO₂ exchange rate at the water-air interface,but the effect of lower wind speed(0?1 m s^-1)on it is not significant.For CH₄,the concentration of CH₄ in river water has a very significant positive correlation with temperature.At the same time,the similar situation also shows in the reservoir area,that is,CH₄ concentration and water temperature have a very significant positive correlation.In addition,it should be pointed out that the contribution rate of CH₄ ebullition flux to the total CH₄ flux is as high as 50%,of which the highest is 80%in October.(4)On the annual scale,the rivers and reservoirs of the Kuye River are atmospheric sustainable carbon sources(CO₂,CH₄).The overall performance of FCO₂ and FCH₄ is:The average FCO₂ of the Kuye River is similar to that of the Yangtze River in my country and foreign temperate rivers,but lower than other tributaries in the middle reaches of the Yellow River;while the average CH₄ emission of Kuye River is similar to that of Guadalete River,a temperate river located in the southwestern part of Andalusia,Spain.