Study On Carbon Dioxide Fluxes Across Water-air Interface In Nihe Reservoir

The static chamber/gas chromatograph techniques was used the first time in China to measure CO₂ fluxes across water-air interface in Nihe reservoir in Harbin.In this paper, observations were conducted to study the character of diurnal variation and seasonal variation of CO₂ fluxes in ice-free seasons including spring,summer and autumn.And meanwhile,the preliminary assessment was given on the situation of carbon source/sink in Nihe reservoir. Through the amount of data analysis,we found that:1.From the seasonal variation view,Nihe reservoir was the source of atmospheric CO₂ in three seasons with the average CO₂ fluxes of 690.42±15.18(mg m-2 d-1).The character of seasonal variation was obvious and their basic trends were:summer>spring>autumn with the average fluxes of 756.42±54.58(mg m-2 d-1),714.16±83.45(mg m-2 d-1) and 600.67±77.14(mg m-2 d-1),respectively.2.From the point view of diurnal variation,all-day performance was source for CO2 in Nihe reservoir.The average carbon flux in three seasons were 26.43±2.52(mg m-2 h-1), 35.44±4.09(mg m-2 h-1),24.52(mg m-2 h-1),respectively.The rules of diurnal variation of CO₂ fluxes were:Day With the solar radiation enhanced in daytime,CO₂ emission reductions, CO₂ flux to reach the minimum at about13:00,and thereafter CO₂ flux increased gradually affected by aquatic organisms' respiration and reached source maximum between 22:00～1:00. Besides the autumn with the diurnal variation trend of bimodal,the spring and summer are reflected in increasing trend of single-peak type.3.The factors that effected variation of c across water-air interface were a little differed between variation of diurnal and seasonal.The main factors impacted on diurnal variation of CO₂ fluxes are:temperature,wind speed,alkalinity and chlorophyll.There was negative relationship between carbon flux and temperature,chlorophyll,and positively correlated with wind speed and alkalinity.While the main factors affected seasonal variation are:temperature, aquatic plants,and water level and weather conditions,respectively.4.The carbon emissions of all-year in Nihe reservoir is 1.01Gt a-1(G=1×10⁹g). Compared with previous studies we found that total emissions of CO₂ in Nihe reservoir located at lower-middle level on the whole which is much less than the water bodies in tropical and subtropical but higher than the ones in cold areas as well as oligotrophic water body.In addition,CO₂ emissions of reservoir are similar to nature lakes.This result is basically corresponded to previous study.