河北平原城市近郊农田大气氮沉降特征

【目的】随着人类活动引起大气活性氮排放的增加,大气氮沉降亦迅速增加,进而影响各区域生态系统。明确河北平原城市近郊农田大气氮沉降的动态变化,可以为农田氮素资源综合管理提供科学依据,也为中国氮素沉降网络提供关键基础数据。【方法】在河北省保定市河北农业大学实验教学基地进行了为期6年(2006—2011年)的湿/混合沉降监测试验以及1年(2011年)的干沉降监测试验。湿/混合沉降通过雨量器自动采集降水;干沉降中气态NH_3、HNO_3和颗粒态铵离子和硝酸根(_pNH_4~+和pNO_3~-)样品通过主动采样DELTA(DEnuder for Long-Term Atmospheric Sampling)系统采集,气态NO_2样品通过被动扩散管采集。【结果】河北保定地区多雨季节为6—9月,占全年(2006-2011年)降雨量的88.6%、81.5%、89.3%、88.9%、74.5%和83.1%;大气氮湿/混合沉降浓度冬、春季较高,夏季最低,冬春两季NH+4~+-N、NO_3~--N、TIN和TDN浓度分别占全年的74.5%、72.6%、74.1%和71.3%;氮湿/混合沉降量亦存在明显的季节性变化,夏季最大,冬季最小;各形态氮湿/混合沉降浓度高低表现为:TDNTINNH+4~+-NNO_3~--N,且与降雨量呈极显著负相关;监测区6年间平均湿/混合沉降总量为32.8 kg N·hm~(-2),其中2008年大气氮湿/混合沉降量最大,达40.4 kg N·hm~(-2),2010年大气氮湿/混合沉降量最小,为28.9 kg N·hm~(-2);大气氮湿/混合沉降中TIN占TDN沉降量75%以上,其中NH+4~+-N是TIN的主要组成部分,占其总量的56.6%—69.7%,平均为64.4%;各形态氮(NH+4~+-N、NO_3~--N、TIN和TDN)湿/混合沉降量与月降雨量、月降雨频次呈极显著正相关;大气氮干沉降中各无机氮(NH_3、NO_2、HNO_3、pNH_4~+、pNO_3~-)浓度有明显的季节性变化特征,且各形态氮的月沉降量变化趋势与氮浓度一致;总体来看,气态氮NH_3、HNO_3、NO_2及颗粒态氮pNH_4~+、pNO_3~-的年沉降量分别达到10.1、7.60、4.39、6.47及3.81 kg N·hm~(-2)。【结论】监测区大气氮沉降量受周边地区工业与当地农田施氮量共同影响,且由干湿沉降共同决定。该地区大气氮沉降量较高,2006—2011年大气湿/混合沉降总量在28.9 kg N·hm~(-2)(2010年)—40.4 kg N·hm~(-2)(2008年)之间,平均为32.8 kg N·hm~(-2);干沉降无机氮总量(2011年)为32.3 kg N·hm~(-2);干湿沉降无机氮总量(2011年)为58.6 kg N·hm~(-2)。

Nitrogen Deposition in Suburban Croplands of Hebei Plain

【Objective】As the rapid intensification of human activities induced the increase of active atmospheric nitrogen, the atmospheric nitrogen deposition has increased significantly, and consequently the response of the regional ecosystems has gradually become obvious. The objective of this study is to investigate the dynamics of wet and dry deposition of atmospheric nitrogen in Hebei plain, to provide a scientific basis for the integrated management of farmland nitrogen resources, and also to provide basic data for the nitrogen deposition network in China.【Method】Experiments of N wet deposition (2006-2011) and dry deposition (2011) were carried out in the experimental teaching base of Hebei Agricultural University in Baoding areas. N wet deposition was collected by a standard rain gage. DELTA active sampling systems were used to collect NH₃, HNO₃, pNH₄⁺ and pNO₃^- . NO₂ samples were collected using Gradko diffusion tubes at sampling sites.【Result】The period from June to September is the rainy season in Baoding area of Hebei, accounting for 88.6%, 81.5%, 89.3%, 88.9%, 74.5% and 83.1% of the annual rainfall in 2006-2011. Monthly N concentration in precipitation was higher in winter and spring than that in summer and autumn, the proportions of NH₄⁺-N、NO₃^--N、TIN and TDN in spring and winter were 74.5%, 72.6%, 74.1% and 71.3%, respectively. The amount of N wet deposition also had an obvious seasonal change, with higher in summer and lower in winter. Annual N wet deposition ranked by the sequence of TDN (total dissolved N) ＞ TIN (total inorganic N) ＞ NH₄⁺-N ＞ NO₃^--N, and had a significant negative correlation with rainfall. The annual N wet deposition during 2006-2011 averaged 32.8 kg N·hm^-2, with the maximum value of 40.4 kg N·hm^-2in 2008 and the minimum value of 28.9 kg N·hm^-2 in 2010. The TIN accounted for more than 75% of TDN deposition,NH₄⁺-N is the major component of TIN accounting for 56.6%-69.7% of the total amount, with an average of 64.4%. Monthly N wet deposition was positively correlated with rainfall and rainfall frequency. Atmosphere concentrations of reactive N (e.g. NH₃, NO₂, HNO₃, pNH₄⁺, pNO₃^-) and their dry deposition also showed large seasonal variations. In general, annual N dry deposition of gases (NH₃, NO₂ and HNO₃) and particles (pNH₄⁺ and pNO₃^-) were 10.1, 7.60, 4.39, 6.47 and 3.81 kg N·hm^-2, respectively. 【Conclusion】The Baoding area deposition contents of nitrogen in atmosphere were affected both by industrial and by agricultural fertilizers, and determined by wet and dry deposition. Atmospheric nitrogen deposition was higher in Baoding area of Hebei, the annual mean N wet deposition was 28.9 kg N·hm^-2 (2010) to 40.4 kg N·hm^-2 (2008), and the averaged N wet deposition (2006-2011) was 32.8 kg N·hm^-2. The N dry deposition was 32.3 kg N·hm^-2 in 2011, and annual N wet and dry deposition were up to 58.6 kg N·hm^-2 in Baoding, Hebei Plain.