摘要:淡水生态系统被认为是大气温室气体排放的重要来源，尤其在人类活动影响下，其排放强度可能进一步增强。城市小型景观水体是城市生态系统的重要组成，具有面积小、数量大以及人类干扰强的特征，其温室气体排放特征及影响因素尚不清楚。选择重庆市大学城8个景观水体和周边2个自然水体为对象，于2019年1、4、7、10月，利用漂浮箱和顶空法分析了水体CO₂与CH₄的溶存浓度及排放通量，旨在揭示城市小型景观水体CO₂与CH₄排放强度、时空变异特征以及影响因素。结果表明，10个小型水体CO₂、CH₄的溶存浓度范围分别为10.75-116.25 μmol/L和0.09-3.61 μmol/L（均值分别为（47.6±29.3）μmol/L、（1.13±0.56）μmol/L），均为过饱和状态；漂浮箱法实测的8个景观水体CO₂和CH₄排放通量均值分别为（72.7±65.9）mmol m^-2 d^-1和（2.31±3.48）mmol m^-2 d^-1（顶空法估算值为（69.7±82.0）mmol m^-2 d^-1和（3.69±2.92）mmol m^-2 d^-1），是2个自然水体的3.5-6.1和2.0-4.5倍，呈较强的CO₂、CH₄排放源；居民区景观水体CO₂和CH₄排放略高于校园区，均显著高于对照的自然水体；CO₂排放夏季最高，秋季次之，冬、春季最低，CH₄呈夏季>秋季≈春季>冬季的季节模式，温度和水体初级生产共同影响CO₂和CH₄排放的季节模式；水生植物分布对景观水体CO₂、CH₄排放有显著影响，有植物分布的水域比无植物水域平均高1.97和2.94倍；漂浮箱法和顶空法测得气体通量线性关系较好，但顶空法测得CO₂通量在春季明显偏低，而CH₄则普遍偏高。相关分析表明，景观水体碳、氮浓度、pH值以及DO等对CO₂排放具有较好的指示性，CH₄排放通量主要与水体中碳、磷浓度有关。城市小型景观水体CO₂、CH₄排放通量远高于大部分已有自然水体的研究结果，呈一种较强的大气温室气体排放源，在区域淡水系统温室气体排放清单中具有重要贡献，未来研究中应给以更多关注。



Abstract:Freshwater ecosystem, as sink of the terrestrial and anthropogenic carbon, is the most active bioreactor for global carbon biogeochemical processes and an important emitter of greenhouse gases (i.e. CO₂ and CH₄) to atmosphere, and then influences the global climate change and carbon cycling. CO₂ and CH₄ emissions from freshwaters have been extensively attentional in recent years given their importance, particularly that the emissions would be further enhanced by the increasing human activities. The urban small-scale landscape water bodies (including landscape pond, lake), featured by small area and large quantity, are a crucial component of urban ecosystem and strongly influenced by human activities. However, greenhouse gases emissions from such artificial-dominated waters are rarely studied and have been badly neglected. In the present study, for exploring the spatiotemporal variations and controls of CO₂ and CH₄ emissions from urban small landscape waters, we selected eight landscape water bodies and two natural water bodies in Chongqing, and carried out four seasonal investigations of CO₂ and CH₄ concentrations and emissions from the surface water in January, April, July and October in 2019 through the static chamber-gas chromatography technique and headspace method. Meanwhile, the vegetated and non-vegetated zones in the sampling water were monitored separately to identify the hydrophyte's disturbance. The result showed that CO₂ and CH₄ concentrations in urban landscape waters in Chongqing were widely supersaturated with range of 10.75-116.25 μmol/L (averaged (42.5±28.7) μmol/L) and 0.09-3.61 μmol/L (average of (0.98±0.80) μmol/L), respectively; the average CO₂ and CH₄ fluxes measured by the floating box method were (72.7±65.9) and (2.3±3.5) mmol m^-2 d^-1 respectively, indicating that the urban landscape waters were the net CO₂/CH₄ emission source. CO₂ and CH₄ emissions from the residential landscape waters were slightly higher than those from the landscape waters in campuses, but both were significantly higher than the two natural waters which were almost impervious to urban activity, suggested that the urban landscape waters could play a crucial contribution to the inland water CO₂ and CH₄ emissions on regional scale. In addition, the distribution of aquatic plants had a significant impact on the CO₂ and CH₄ emissions of landscape waters with that the emission flux from non-vegetated water was universally smaller than that from vegetated zone. CO₂ and CH₄ fluxes from urban landscape waters presented obviously seasonal patterns, there into, CO₂ fluxes were the highest in summer, followed by autumn, and the lowest in winter and spring, while CH₄ fluxes in summer were higher than that in autumn and spring, significantly higher than winter. Temperature was the critical factor determining the seasonal variation of CH₄ and CO₂ emissions, while CO₂ flux was also affected by water primary production. CO₂ emissions of landscape waters were significantly associated with the factors such as pH, nitrogen, carbon concentration and dissolved oxygen. Meanwhile, CH₄ emissions were mainly related to the carbon and phosphorus concentrations in surface water. The CO₂ and CH₄ fluxes from urban small landscape water bodies in this study were much higher than most of the previous survey on natural lakes, reservoirs and ponds, which highlighted the landscape waters may be a strong source of greenhouse gas emissions to the atmosphere, and plays a vital role in the greenhouse gas emission inventory from global or regional freshwater system, and thus more attention should be paid in future.





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