新疆天山北坡中段森林生态系统氮素干沉降

Atmospheric Nitrogen Dry Deposition in Forest Ecosystem in the Central Tianshan Mountains,Xinjiang

在过去几十年,干旱半干旱地区由于人为活动的增强引起了大气活性氮污染的加剧,从而导致氮沉降量的增加。为了定量评估新疆天山中段雪岭云杉(Picea schrenkiana)针叶林大气氮素干沉降状况,自2012年10月至2013年9月,选择在乌鲁木齐县萨尔达坂乡森林生态系统,利用中流量大气颗粒物采样器和被动采样器,距离地表2 m处分别采集PM_(10)(可吸入颗粒物)和NH_3、NO_2样品,基于推算法定量评价氮素干沉降通量。结果表明:研究区NH_3、NO_2、颗粒态NH^+_4(p NH^+_4)、颗粒态NO^-_3(p NO^-_3)和PM_(10)年平均浓度分别为(5.86±1.31)、(2.85±0.30)、(0.45±0.07)、(0.45±0.06)μg·m^(-3)和(55.8±6.52)μg·m^(-3);气态NH_3^-N、NO_2^-N和颗粒态NO^-_3^-N、NH^+_4^-N的沉降通量分别为3.42、0.79、0.61、0.62 kg·hm^(-2)·a^(-1),干沉降总量为5.44 kg·hm^(-2)·a^(-1)。其中,气态NH_3沉降占干沉降总量的62.9%,表明放牧引起的氨排放可能是该地区大气氮沉降的主要来源。鉴于该地区可观的氮干湿沉降总量(9.9 kg·hm^(-2)·a^(-1),其中湿沉降为4.45 kg·hm^(-2)·a^(-1)),对研究区植被、土壤以及自然环境产生的可能影响应引起重视。

Atmospheric nitrogen（ N） deposition has increased largely in arid and semiarid ecosystems over the past three decades due to the increase of human activities. In order to quantitatively estimate the atmospheric N dry deposition in a Picea schrenkiana forest in the central Tianshan Mountains,the atmospheric concentrations of gasphase NH3 and NO2and particulate ammonium and nitrate（ p NH＋4and p NO-3） were monitored using the passive samplers and particulate samplers at 2-m height above soil surface during the period from October 2012 to September 2013. In the study area,the annual mean concentrations of NH3,NO2,p NH＋4and p NO-3were（ 5. 86 ±1. 31）,（ 2. 85 ± 0. 30）,（ 0. 45 ± 0. 07） and（ 0. 45 ± 0. 06） μg·m（-3）respectively,and these revealed that the seasonal variation was significant. Annual mean concentration of PM（10）was（ 55. 8 ± 6. 52） μg·m（-3）with a maximum value of 87. 0 μg·m（-3）occurred in April. The annual atmospheric N dry deposition was 5. 44 kg·hm（-2）·a（-1）,and the averaged fluxes of NH3,NO2,particulate ammonium and nitrate（ p NH＋4and p NO-3） were 3. 42,0. 79,0. 61 and 0. 62 kg·hm（-2）·a（-1）respectively. Compared with other Nr species,NH3（ 62. 9%） was dominant in total Nr dry deposition in the forest ecosystem in the central Tianshan Mountains,which revealed that NH3 from livestock or grazing animals could be the major source of atmospheric nitrogen deposition. Considering the total dry and wet N depositions of 9. 9 and 4. 45 kg·hm（-2）·a（-1）,we should pay more attention to the potential impacts of N deposition on vegetation,soil and natural environment in the study area.