Greenhouse Gases Emission Characteristics Of Rivers In Nanjing And The Influencing Factors

Global warming, one of the most important environmental and development issues, related to greenhouse gases (GHGs) emissions caused by human activities closely. River ecosystem plays an important role in the global greenhouse gas balance, and it has caused wide attention of scholars both at home and abroad in recent years. By employing floating static chamber-chromatography method, GHGs fluxes, which include CO2、CH4、N2O, at the water-air interface of four rivers (Tuanjie River, Jinchuan River, Inner and Outer Qinhuai River) and two reservoirs (Dingjie Reservoir and Jinniu Reservoir) were continuously monitored in Nanjing during2012-2013. And based on these observed data, the variation, influencing factors and emission mechanism of GHGs fluxes were analysed to provide a reference for the urban greenhouse gas emissions inventory preparation and environmental pollution control.The main results are as follows:(1) During diurnal variation, the four rivers were all the source of emissions of CH4and CO2. Jinchuan and Tuanjie river absorbed N2O in nighttime and emitted N2O in daytime. Inner and Outer Qinhuai acted as the sources of N2O emission. Jinniu lake overall performed as the sink of CO2and N2O. Parts of high emissions are mainly influenced by the changes of hydrodynamic conditions, but the environmental factors still play a considerable role in the entire trend.(2) Dividing the diurnal variation into daytime and nighttime fluxes, we found that more than half of the nighttime emissions account for40%of fluxes throughout the day. So the observation of fluxes during the night should be also considered seriously. For natural rivers, the proper sampling period is relatively consistent with other studies (9:00-11:00), but for the river subjected to interference, the sampling period should take into account the specific characteristics of the local conditions.(3) Fluxes of greenhouse gases (CH4, CO2and N2O) in the four rivers showed different seasonal variations. But on the whole, CH4and CO2emitted most in summer or the turn of the season,while the fluxes of N2O reached an emission peak in winter. According to the regional division, the average emissions of greenhouse gases exhibt a trend as follows:suburban watershed> urban watershed>natural water bodies.(4) Considering the water body separately, greenhouse gases (CH4, CO2and N2O) emissions were negatively correlated to relative humidity, and content of chlorophyll a. When taking into account of all water bodies of three greenhouse gas fluxes and water quality parameters, CH4, CO2, N2O emission flux showed a positive correlation with COD, NO2-N, TP, TN, conductivity, a highly significant negative correlation with DO. Both of CH4and CO2have a significant negative correlation with the pH value.