我国雷州半岛典型农田大气氮沉降研究

Abstract

近一个半世纪以来，粮食和能源需求导致活性氮创造的急剧增加，从而导致各种活性氮的排放及其沉降的增加。氮沉降引起土壤酸化，水体富营养化，及敏感生态系统植物多样性的丧失等不良生态效应。因此定量不同生态系统氮沉降量对于确定该地区生态系统安全及氮循环有重要意义。南方地区氮沉降已有较多研究，主要集中于湿沉降的研究，选取雷州半岛地区典型农田综合研究了大气氮素的干湿沉降。结果表明：大气活性氮浓度NH₃、HNO₃、NO₂、pNH₄⁺和pNO₃^-浓度分别为5.62、0.88、3.16、3.30、2.02 μg N/m³。采用欧洲氮沉降监测网的氮干沉降速率估算了大气氮干沉降量为17.6 kg N hm^-2 a^-1。大气降雨NO₃^--N浓度为 （0.86±0.36） mg N/L， NH₄⁺-N浓度为（1.11±0.68） mg N/L，大气降雨无机氮含量冬季最高，夏季最低。大气无机氮年湿沉降总量为25.3 kg N/hm²。湿沉降NH₄⁺-N和NO₃^--N， 干沉降NH₃、HNO₃、NO₂、pNH₄⁺、pNO₃^-分别占沉降量的30.8%、28.0%、23.7%、5.4%、2.8%、3.9%、5.4%。湿沉降NH₄⁺和干沉降NH₃在氮沉降中占主导地位显示氮肥施用导致的NH₃挥发对大气活性氮浓度及氮沉降的显著贡献。鉴于研究可观的氮沉降量（总沉降量42.9 kg N hm^-2 a^-1），其向农田的养分的输入不容忽视； 氮沉降对该地区水体，自然生态系统的环境影响需要受到重视。;Reactive nitrogen (Nr) creation has increased sharply over the past 150 years because, as the world population has increased, food and energy consumption have also increased continuously. Consequently, Nr emissions and nitrogen deposition have increased rapidly since the Industrial Revolution. Nitrogen deposition causes a series of environmental problems, including soil acidification, water eutrophication, loss of plant diversity in sensitive ecosystems and indirect N₂O emissions. The Leizhou Peninsula is famous for cash crop cultivation. Because of the specific meteorological characteristics of this area, for example, the high air temperature, high annual rainfall and strong winds, quantifying nitrogen deposition may be very important for evaluating nitrogen cycling in cropland and other related environmental impacts. Previous studies undertaken in this area have considered wet nitrogen deposition. In our study, we investigated total wet and dry nitrogen deposition in a typical cropland in Zhanjiang. The atmospheric concentrations of NH₃, HNO₃, NO₂, pNH₄⁺ and pNO₃^- were 5.62, 0.88, 3.16, 3.30 and 2.02 μg N/m³, respectively, over the duration of the sampling period. The peak NH₃ concentration was observed in summer, and was attributed to NH₃ emission simulation from different NH₃ emission sources (especially N fertilization), induced by high temperatures. pNH₄⁺ and pNO₃^- concentrations were higher in winter due to the low winter rainfall, as were inorganic nitrogen concentrations in precipitation. Atmospheric Nr concentrations were much higher than those reported by the European and American Nr monitoring networks, but much lower than those reported in the North China Plain. Dry nitrogen deposition is difficult to estimate directly because of the complicated meteorological and surface conditions. In this study, we tried to choose reasonable deposition velocities from those summarized in the literature from other studies. The American Clean Air Status and Trend's Network only has data for HNO₃, pNO₃^-, and pNH₄⁺ deposition velocities, and so could not be used in this present study. However, we were able to use the deposition velocities adopted by the European monitoring network. These were considered appropriate because we used the same equipment as was used to monitor nitrogen deposition in the European NitroEurope network. The NH₃, HNO₃, NO₂, pNO₃^- and pNH₄⁺ deposition velocities from this network were 0.53cm/s, 0.8 cm/s, 0.12 cm/s, 0.25 cm/s and 0.25 cm/s, respectively, while the dry nitrogen deposition rate was 17.6 kg hm^-2 a^-1. The average NO₃^--N concentration in precipitation samples was (0.86 ± 0.36) mg N/L, while the average NH₄⁺-N concentration was (1.11 ± 0.68) mg N/L. Inorganic nitrogen concentrations in precipitation samples were higher in winter and lower in summer because of the variation in rainfall between the different seasons. The total wet nitrogen deposition was 25.3 kg N hm^-2 a^-1. Wet NH₄⁺-N and NO₃^--N, and dry NH₃, HNO₃, NO₂, pNH₄⁺ and pNO₃^- contributed 30.8%, 28.0%, 23.7%, 5.4%, 2.8%, 3.9% and 5.4% to the total nitrogen deposition, respectively. The large contributions from wet NH₄⁺-N deposition and dry NH₃ deposition in this study indicated that fertilization played a large role in airborne NH₃ and nitrogen deposition. Comparison of the inorganic nitrogen concentrations in rainfall in other regions of China shows that the NH₄⁺-N concentrations and NO₃^--N concentrations in the Leizhou Peninsula were much lower than those for the North China plain, but that they were consistent with the inorganic nitrogen concentrations reported for southern and eastern China. The total nitrogen deposition recorded during this study was 42.9 kg N hm^-2 a^-1. Wet nitrogen deposition rates showed a close relationship with rainfall events, showing that wet nitrogen deposition changes with the rate of rainfall in different years. Dry deposition velocities of Nr species should be measured directly, or by using inferential methods, to decrease uncertainty in dry nitrogen deposition studies. Further, there should be some concern about cropland nutrient management and the related impacts on water, forest and grassland because of the high rates of background nitrogen deposition in this area.