中国东部地区无机氮湿沉降: 南-北不同类型监测点的比较

中国被认为是全球氮沉降热点地区之一,东部地区作为经济发达和人口密集区域,更是人为活性氮大气排放和沉降的高发区,但针对我国整个东部不同生态系统的氮沉降及其南北区域特征差异的报导较少.2011—2013年,选择在我国东部的12个监测点(南北各6个,均包括城市、农村和背景点3种类型)利用传统雨量器(型号SDM6A)进行连续3年的氮素湿沉降观测.结果表明: 监测点降水中铵态氮、硝态氮和总无机氮沉降浓度波动范围分别为0.62～2.76、0.54～2.50和1.25～4.92 mg N·L^-1,平均浓度分别为1.4、1.5和2.9 mg N·L^-1,北方监测点的雨水中各活性氮浓度均高于南方监测点.12个监测点降水中铵态氮、硝态氮和总无机氮的湿沉降量的波动范围分别为7.0～18.3、6.9～18.9和14.9～32.6 kg N·hm^-2·a^-1,平均值分别为11.5、12.2和23.7 kg N·hm^-2·a^-1.北方不同类型监测点间存在显著差异,表现为:城市监测点(26.3±6.4 kg N·hm^-2·a^-1)>农村监测点(21.8±3.5 kg N·hm^-2·a^-1)>背景点(15.5±1.3 kg N·hm^-2·a^-1);与之相反,南方各监测点氮素湿沉降无显著差异,城市、农村和背景点的湿沉降量分别为(26.8±2.7)、(25.5±2.9)和(20.5±2.4) kg N·hm^-2·a^-1.除城市监测点外,南方的农村和背景点的氮素湿沉降量均高于北方相应类型的监测点.表明我国东部的南北各区域(包括背景地区)均面临较高水平的大气氮沉降,其引发的生态环境风险问题应加以重视.

Inorganic nitrogen wet deposition in eastern China: Comparison of different land use-based monitoring sites in north and south regions

China is one of the global hotspots of atmospheric nitrogen (N) deposition. This is especially true for eastern China, an economically developed and densely populated area, which emits large quantities of anthropogenic reactive N species to the air and experiences high levels of atmospheric N deposition. Few studies, however, have examined spatial variations of N deposition across different ecosystems in northern and southern regions of eastern China. Using the traditional rain gauge (SDM6A) method, we conducted a three-year (2011-2013) study to quantify wet N deposition fluxes at twelve sites (six northern and six southern monitoring sites, covering urban, rural and background land use types) in China. The annual volume-weighted mean (VWM) concentrations of NH₄⁺-N, NO₃^--N and total inorganic N (TIN) atmonitoring sites were in the ranges of 0.62-2.76, 0.54-2.50 and 1.25-4.92 mg N·L^-1, and averaged 1.4, 1.5 and 2.9 mg N·L^-1, respectively. Northern sites showed higher concentrations of N species in precipitation than southern sites. Annual deposition fluxes of NH₄⁺-N, NO₃^--N and TIN were in the ranges of 7.0-18.3, 6.9-18.9 and 14.9-32.6 kg N·hm^-2·a^-1, averaging 11.5, 12.2 and 23.7 kg N·hm^-2·a^-1, respectively. There were significant differences in total N deposition fluxes among different land use types in the north, showing the decreasing order of urban sites (26.3±6.4 kg N·hm^-2·a^-1)> rural sites (21.8±3.5 kg N·hm^-2·a^-1)> background (15.5±1.3 kg N·hm^-2·a^-1). Total N deposition fluxes at urban, rural and background sites in the south were (26.8±2.7), (25.5±2.9) and (20.5±2.4) kg N·hm^-2·a^-1, respectively, showing no significant spatial variation. While urban sites did not show obvious regional differences, total N wet deposition fluxes at rural and background sites in the south were significantly higher than those at corresponding sites in the north. Our results revealed that both south and north regions of eastern China (including background areas) are receiving high levels of wet N deposition and associated ecological and environmental risks should be considered.