Study On CO₂Fluxes Across Water-air Interface In Peatland Reservoirs Around Harbin

The static chamber/gas chromatography was used to conduct a comprehensive observation on CO2flux across water-air interface in northern peat-type reservoir ecosystem. Our research chose two large reservoirs Nihe and Xiquanyan as the main subject in Harbin, Heilongjiang province. According to the observation conducing in ice-free season (spring, summer, autumn) with average200days, we studied the spatial and temporal variation of CO2flux and discussed deeply on the environmental factors affecting CO2flux. We hope the results will give some data support for the regular research of CO2flux in reservoir ecosystem and its contribution to global climate change.By a large number of data analysis, we found that:(1) The diurnal variation of CO2flux across water-air interface in reservoirs is obviousAccording to the research, reservoir ecosystem was overall the source of atmospheric CO2. Diurnal variation of CO2flux is obvious. From seasonal perspective, the basic trend of Nihe Reservoir was:Summer756.42±54.58(mg m-2d-1)> Spring714.16±83.45(mg m-2d-1)> autumn600.67±77.14(mg m-2d-1). With a slightly difference the Xiquanyan Reservoir’trend was:Spring787.42±43.03(mg m-2d-1)> autumn409.24±13.64(mg m-2d-1)> Summer255.21±28.2(mg m-2d-1). While from the perspective of diurnal variation, the two reservoirs were similar:the CO2flux of day was less than that of night. Especially in June and July the difference was obvious with high rate of121%between day and night. The minimum value of CO2flux generally showed up at13:00in the afternoon, and maxima value appeared at21:00or1:00.(2) The feature of spatial heterogeneity was found in CO2flux across water-air interface in reservoirs.According to analysis, we found that there was certain spatial heterogeneity of CO2flux in the reservoirs. The CO2flux of sampling spots in Nihe was the water outlet> reservoir center> water inlet successively. The CO2flux of Xiquanyan was A>C>D> B. The main factors affecting the spatial variation of CO2flux were the change of reservoir level and fluctuating zone, and distribution of aquatic plant and species composition, respectively.(3) The factors impact CO2flux across water-air interface of the reservoir is complexCO2fluxes across water-air interface involving more impact factor which is divided into three categories,①climatic condition factors including wind speed, temperature and weather conditions, in which the influence of temperature on CO2flux is the most notable with significant negative correlation. It was positively correlated between wind speed and carbon flux.②water physical and chemical factors including DOC, water level, alkalinity, TP, TN and pH, etc.③biological factors mainly refers to the impact of aquatic plants on carbon fluxes, the negative correlation between chlorophyll and carbon fluxes can be effective confirmed. Moreover, impact factors on temporal and spatial variations of carbon flux were different.(4) CO2flux estimate of peat-type reservoirs and comparison with different areasThe estimate was made on CO2flux emissions from the two reservoirs, Nihe and Xiquanyan. The result showed that annual carbon emissions of two reservoirs was similar with value of1.01Gt a-1and1.08Gt a-1(G=1×109g), respectively. By contrast to the details of the carbon fluxes of two reservoirs, we found that physicochemical characteristics of the reservoir, location, water eutrophication and type of aquatic plants were important factors impacting CO2fluxes. Comparing with the results of reservoirs from different latitudes and regions, total CO2emissions of northern peat-type reservoirs was not significant as some scholars expected. It was higher than the ones in cold areas and oligotrophic water. But significantly lower than the ones in tropical and subtropical areas. Accually, the CO2emissions of two reservoirs were close to nature lakes.(5) Suggestions for reducing emissions of the greenhouse gas from reservoir ecosystem①strengthen the control of water quality from upstream of reservoir;②optimize the type and structure of the vegetation in the reservoir;③values the importance role of fisheries carbon sinks in reservoir.