城市景观水体是大气CO2与CH4的排放热源,而水生植物作为景观水体的重要组成要素,对水体温室气体排放动态的影响并不清楚。选择重庆市观音塘国家湿地公园为研究区,利用漂浮箱法与顶空平衡法对观音塘水域7种不同水生植物分布区进行水-气界面CO2与CH4排放通量及CO2、CH4溶存浓度进行季节性监测,估算了植物传输对气体通量的贡献。结果表明:1)观音塘水体CO2与CH4浓度范围分别为8.0-341.8 μmol/L和0.23-5.26 μmol/L,排放通量分别为26.5-869.1 mmol m-2 d-1和0.40-11.15 mmol m-2 d-1,是大气净CO2与CH4排放源;2)观音塘开敞水区CO2与CH4排放通量低于大部分城市湖泊或景观水体,但植物覆盖区气体通量显著高于开敞水区,表明水生植物增强了景观水体温室气体排放;初步估算植物传输作用(非扩散通量)对水体CO2与CH4排放通量的贡献约为7.3%-44.6%与52.1%-63.4%,狐尾藻对CH4传输作用最强,睡莲、水葫芦次之,菖蒲、再力花、梭鱼草等挺水植物略低,苦草最弱,植物传输作用并未表现出明显的生活型差异;3)水体CO2与CH4浓度及排放通量季节变化显著,温暖季高于寒冷季,植物生长期变化与温度波动是主导水体CO2与CH4排放季节模式及变异强度的主要因素;4)水生植物覆盖区水体营养盐浓度、pH值、DO等因素与CO2、CH4排放通量呈显著的相关性,表明不同植物覆盖导致水生境的分异是影响水体CO2与CH4排放动态及变异性的重要机制。水生植物对水体温室气体产生、输移、排放等具有多重复杂机制,但总体增强了景观水体的温室气体通量,在未来城市水生态管理中应予以更多的关注。
Urban landscape water is a hotspot of carbon dioxide (CO2) and (CH4) emissions to atmosphere, while little is known about the effect of aquatic plants, which is an important component of landscape water ecosystem, on greenhouse gas emissions dynamics in such water. In this study, we selected the Guanyin Pond National Wetland Park in Chongqing as a typical urban landscape water to carry out seasonal investigations for the fluxes and dissolved concentrations of CO2 and CH4 using floating chamber method and headspace method. The aims of this study were to explore contribution of aquatic plants to the spatio-temporal variations in aquatic CO2 and CH4 fluxes in urban landscape waters. The results showed that the concentrations of CO2 and CH4 ranged from 8.0-341.8 μmol/L to 0.23-5.26 μmol/L in Guanyin Pond, and the fluxes of CO2 and CH4 were ranging from 26.5 to 869.1 mmol m-2 d-1 and from 0.40 to 11.15 mmol m-2 d-1, respectively. Guanyin Pond was a net source of atmospheric CO2 and CH4. CO2 and CH4 fluxes in the open water area of Guanyin Pond were much lower than most of the reported values from ponds and lakes in urban area, while those in water area with aquatic vegetations distribution were much higher, indicating the aquatic plants enhanced the greenhouse gas emission of landscape water bodies. It was estimated that the plant transport contributed about 7.3%-44.6% and 52.1%-63.4% of total CO2 and CH4 fluxes from water-air surface, respectively. The contribution of plant transmission was different for different species despite no "biotype effect". The seasonal variations of CO2 and CH4 concentrations and fluxes in Guanyin Pond were significant with higher values in warm season and lower ones in cold season. We highlighted that the seasonal periodicity growth and temperature were main drivers for the seasonal patterns and variation intensity of CO2 and CH4 fluxes. Nutrients concentrations, pH and dissolved oxygen (DO) were influenced by aquatic vegetations distribution in Guanyin Pond, and were significantly correlated with CO2 and CH4 fluxes, indicating that the differentiation of water habitats caused by different aquatic plant species were important mechanism affecting the spatial variability of CO2 and CH4 dynamics. Despite mechanisms of aquatic plant impact on water CO2 and CH4 dynamics are complicated and various, aquatic plant distribution indeed enhance greenhouse gases fluxes of urban landscape water. Therefore, more attentions should be paid to the CO2 and CH4 dynamics in such special aquatic system in the future.