Dissolved greenhouse gas concentrations and the influencing factors in different vegetation zones of an urban lake

为了解城市湖泊不同水生植被区水体温室气体的溶存浓度及其影响因素，于2015年4-11月按每月2次的频率采用顶空平衡法对聊城市铃铛湖典型植被区——菹草区、莲藕区和睡莲区表层水中CO₂、CH₄和N₂O的溶存浓度进行监测，计算水中温室气体的饱和度和排放通量，并测定水温（T）、pH、溶解氧（DO）、叶绿素a及营养盐浓度等理化指标，以探究水体环境因子对温室气体溶存浓度的影响.结果表明，铃铛湖各植被区水体温室气体均处于过饱和状态，是大气温室气体的源；莲藕区CH₄浓度、饱和度和排放通量均显著高于菹草区，而各植被区N₂O和CO₂均无显著性差异；不同植被区湖水中DO、总氮（TN）、总磷（TP）和硝态氮（NO₃^--N）浓度具有显著差异，其中DO、TN和NO₃^--N浓度均表现为菹草区最高，莲藕区最低，而TP浓度则正好相反；各植被区温室气体浓度和水环境参数间的相关分析和多元回归分析的结果表明，水生植物可通过影响水体的理化性质对温室气体的产生和排放产生显著差异影响，在菹草区亚硝态氮（NO₂^--N）、NO₃^--N、T和DO是控制水体温室气体浓度的主要因子；睡莲区为TP和pH；莲藕区则为pH、NO₂^--N和DO.;Dissolved concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the surface water were measured using the headspace equilibrium method fortnightly from April to November of 2015 in the Potamogeton crispus zone, Nymhaea tetragona zone and Nelumbo nucifera zone of the Lake Lingdang in Liaocheng City. The saturations and emission fluxes of the greenhouse gases were calculated based on the two-layered diffusion model. Moreover, water temperature, pH, dissolved oxygen (DO), chlorophyll-a and the nutrient concentrations in the water body were also measured in order to investigate their influences on the dissolved greenhouse gas concentrations. The results showed that the dissolved concentrations of greenhouse gases in different vegetation zones were all supersaturated, which indicated that Lake Lingdang was a source of atmospheric greenhouse gases. The concentrations, saturations and emission fluxes of CH₄ in N. nucifera zone were significantly higher than those in P. crispus zone but no significant difference between the data of N₂O and CO₂ in different vegetation zones. The concentrations of DO, total nitrogen (TN), total phosphorus (TP) and nitrate (NO₃^--N) in three vegetation type zones also had significant differences. The average concentrations of DO, TN and NO₃^--N were highest in the P. crispus zone and lowest in the N. nucifera zone, but it was on the contrary for the average TP concentrations. The results of correlation analysis and multivariate regression analysis between the greenhouse gases and the water environment parameters suggested that the aquatic plants could affect the production and emission of greenhouse gases by influencing the physicochemical properties of water body. Greenhouse gas concentrations in lake water were mainly correlated to NO₂^--N, NO₃^--N, water temperature and DO in the P. crispus zone, while mainly correlated to TP and pH in the N. tetragona zone, and pH, NO₂^--N and DO in the N. nucifera zone.