川西平原小流域不同水体N_(2)O排放特征及驱动因素

Characteristics and driving factors of N_(2)O emission from different waters in a small watershed of the Western Sichuan Plain

氧化亚氮(N_(2)O)是一种潜在的、强大的温室气体,应该根据京都议定书规定开展监测和削减。河流、水库、鱼塘和沟渠等受人类影响的小流域水生生态系统是氮素生物地球化学循环的活跃区域,更是N_(2)O重要的源和汇。然而,同一流域不同水体N_(2)O的排放特征差异及其驱动因素尚不清楚。因此,选择川西平原西河流域作为研究区,于2016年6月到2017年5月连续监测不同水体水气界面的N_(2)O排放强度,并结合聚类分析解析N_(2)O排放特征的驱动因素。结果显示,不同水体的N_(2)O年排放通量差异显著,沟渠的N_(2)O年排放通量最高((52.68±36.09)μg m^(-2) h^(-1)),城市段河流和鱼塘次之((34.16±23.97)μg m^(-2) h^(-1)和(29.03±31.41)μg m^(-2) h^(-1)),乡镇段和农区段河流再次((8.32±28.60)μg m^(-2) h^(-1)和(8.52±9.43)μg m^(-2) h^(-1)),水库最低((-16.45±29.76)μg m^(-2) h^(-1))。除水库表现为N_(2)O的汇,其他水体均表现为N_(2)O的排放源。另外,不同水体N_(2)O排放的季节特征差异显著,农区段河流和农业沟渠表现为夏天最高,冬春最低(P<0.05),而其他水体均表现为冬春显著高于夏秋(P<0.05)。根据N_(2)O排放季节特征及其驱动因素可将西河流域水体分为四类:第一类农业类水体的N_(2)O排放季节特征受气象因素和农业活动的联合驱动;第二类城乡类河流和第三类鱼塘分别受控于人类活动和养殖活动,与降雨温度等气象指标关系较弱;第四类水库主要受控于气象因素。并且,第一类农业类水体已成为大气N_(2)O排放的重要源,农业氮素管控是区域控制N_(2)O排放的重点。

Nitrous oxide(N_(2)O)is a powerful,long⁃lived greenhouse gas that should be monitored and reduced under the Kyoto Protocol.Aquatic ecosystem in small and human⁃impacted watershed,including river,reservoir,fishpond and ditch,is the vital area for biogeochemical cycle of nitrogen as well as the important source and sink for N_(2)O.However,flux,seasonal patterns and driving factors of N_(2)O emission from different aquatic ecosystems are still unknown.To help address this knowledge gap,monthly flux of N_(2)O emission from different aquatic ecosystems were measured from June 2016 to May 2017,and driving factors of N_(2)O seasonal emission pattern were researched by Cluster analysis and Pearson correlation analysis in Xihe watershed,west of Sichuan Province,China.The results show that annual flux of N_(2)O emission varied from different aquatic ecosystems,which were ranged as follow:ditch((52.68±36.09)μg m^(-2) h^(-1))>urban river((34.16±23.97)μg m^(-2) h^(-1))>fish pond((29.03±31.41)μg m^(-2) h^(-1))>rural and agricultural river((8.32±28.60)and(8.52±9.43)μg m^(-2) h^(-1))>reservoir((-16.45±29.76)μg m^(-2) h^(-1)).Ditch,river and fish pond,which were influenced by human activities,were sources of N_(2)O emissions.While,reservoir,which was hardly affected by human beings,was the sink of N_(2)O.In addition,seasonal pattern of N_(2)O emission varied from different aquatic ecosystems.Mean N_(2)O emissions during summer were higher than winter and spring in agricultural river and ditches significantly(P<0.05).While,mean N_(2)O emissions during winter and spring were higher than summer and fall in other rivers,fish pond and reservoir significantly(P<0.05).Finally,the aquatic ecosystems were divided into four types in terms of seasonal patterns and drivers of N_(2)O emission.Agricultural river and ditches were the typeⅠaquatic ecosystems,and their seasonal patterns ofN_(2)O emission were driven by meteorological indicators and agricultural activities.Ruralurban rivers and fishpond were the typeⅡand typeⅢaquatic ecosystems,and their seasonal patterns of N_(2)O emission showed weak relationship with precipitation and temperature,but were driven by ruralurban activities and aquaculture management,respectively.Reservoir was the typeⅣaquatic ecosystems,and its seasonal patterns of N_(2)O emission had negative relationship with temperature significantly(P<0.05),suggesting that it was driven by meteorological indicators.In this study,the typeⅠaquatic ecosystems(agricultural river and ditches)has become the most important source of N_(2)O emission,and N loss control during agricultural activities was the most important measure for N_(2)O emission control.