生态学报  2014, Vol. 34 Issue (19): 5541-5548

文章信息

骆晓声, 石伟琦, 鲁丽, 刘学军, 莫亿伟, 邓峰
LUO Xiaosheng, SHI Weiqi, LU Li, LIU Xuejun, MO Yiwei, DENG Feng
我国雷州半岛典型农田大气氮沉降
Nitrogen deposition in typical cropland in the Leizhou Peninsula, China
生态学报, 2014, 34(19): 5541-5548
Acta Ecologica Sinica, 2014, 34(19): 5541-5548
http://dx.doi.org/10.5846/stxb201301070050

文章历史

收稿日期:2013-1-7
网络出版日期:2014-3-7
我国雷州半岛典型农田大气氮沉降
骆晓声1, 石伟琦2 , 鲁丽1, 刘学军1, 莫亿伟2, 邓峰2    
1. 中国农业大学资源与环境学院, 北京 100193;
2. 中国热带农业科学院南亚热带作物研究所, 湛江 524091
摘要: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。
关键词雷州半岛    活性氮    干沉降    湿沉降    
Nitrogen deposition in typical cropland in the Leizhou Peninsula, China
LUO Xiaosheng1, SHI Weiqi2 , LU Li1, LIU Xuejun1, MO Yiwei2, DENG Feng2    
1. China Agricultural University, College of Resources and Environmental Sciences, Beijing 100193, China;
2. South Subtropical Crops Research Institute Chinese Academy of Tropical Agricultural Science, Zhanjiang 524091, China
Abstract: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.
Key words: Leizhou Peninsula    reactive nitrogen    dry deposition    wet deposition    

氮素是自然界中所有生物必需的生长元素,控制着一些生态系统的初级生产力[1]。N2约占大气组分的78%,由于破坏氮分子之间的氮原子三键需要能量,对于大多数生物都不能直接利用大气中的氮气。人为活动导致大气活性氮创造的迅速增加,工业革命前人为活动产生的活性氮仅为15 Tg N/a,到20世纪中期人为活动创造的活性氮达到156 Tg N /a[2]。大量的活性氮创造也相应导致大气活性氮排放及其沉降的随后增加[2, 3]。大气氮沉降的增加破坏生态环境,如:诱导土壤酸化,水体富营养化;减少生态系统的物种多样性;增加温室气体的排放等[4, 5, 6]

改革开放后,随着中国社会经济的快速发展,活性氮的创造速度以每年3.7%的速度增长,到2010年中国大陆创造的活性氮达到56Tg(1 Tg = 1012g)[7],相应也导致大气NH3及NOx排放的急剧增加[8]。大量的活性氮排放也使中国一些地区成为高氮沉降量的热点地区[2]。充分利用以大气氮沉降为主体的环境养分资源,减少氮肥的不合理投入,是实现养分资源高效利用的重要途径[9]。雷州半岛(湛江)是中国重要的糖蔗、水果、蔬菜、桉树、剑麻生产基地。以前该地区氮沉降研究也有报道,但主要集中于湿沉降的研究[10, 11]。本研究综合分析了雷州半岛典型农田采样点大气氮素的干湿沉降,以期为该地区农田生态系统的氮循环及氮肥高效利用提供理论依据。

1 材料与方法 1.1 采样点简介

实验点位于广东省雷州半岛的湛江市,属热带季风气候,年均气温23.0 ℃,降雨量1500mm左右;全年日照约2000h,雨热同期;年平均雷击天数200多天,是世界第二雷区。具体位置为湛江市麻章区中国热带农业科学院南亚热带作物研究所植物营养学科基地,毗邻世界地质公园-湖光岩,距市区大概20 km。地理坐标为东经110°17′,北纬21°12′,海拔高度9 m。土壤类型为凝灰岩砖红壤,土壤pH值为4.5。周围无工厂,主要以种植业为主。种植的作物有:香蕉、菠萝、荔枝、龙眼等果树及桉树、榕树、发财树等园林绿化树种。施肥量平均为400 kg N hm-2 a-1,P2O5 100 kg hm-2 a-1,K2O 600 kg hm-2 a-1。施用的氮肥主要为尿素。

1.2 干沉降的活性氮的收集方法

活性氮气体NH3、HNO3及颗粒态铵和硝采用英国生态水文中心开发的DELTA(DEnuder for Long-Term Atmospheric sampling)系统收集。采样器内有一个小泵(0.3—0.4 L/min)与制作的采样链相连,使进入的气体活性氮组分被采样链内扩散管上的吸附剂吸附,颗粒物被后面的滤膜收集。其中采样链收集硝酸的吸附剂为1% KOH+1% 甘油甲醇溶液。吸附氨气的扩散管添加吸附剂为5% 柠檬酸甲醇溶液。收集颗粒物硝加吸附剂为5% KOH+10%甘油甲醇溶液。收集颗粒物铵加吸附剂为13% 柠檬酸甲醇溶液。采样后,收集硝酸的扩散管用6 mL 0.05%的双氧水浸提,颗粒态硝的滤膜用10 mL 0.05%的双氧水浸提;收集氨气的扩散管及颗粒态铵的滤膜用高纯水浸提,其中,收集氨气的扩散管用6 mL高纯水浸提,铵根离子用10 mL高纯水浸提。关于DELTA系统更详细的资料见参考文献[12]。采样周期为1个月,采样高度为1.6 m,采样从2010年8月开始到2012年5月结束。采样同时采集空白样品,在分析过程中严格控制质量,防止样品被污染。采用流动分析仪(BRAN LUEBBE autoanalyzer 3 (AA3),Germany)测定浸提液的NH+4-N和NO-3-N浓度。采样器记录采样开始及结束时的空气体积,根据测得的浸提液体积,浓度,及所采集大气的体积计算各种活性氮种类在大气中的含量。用公式表示为:

χa= (Ce-Cbν/V

式中,χa表示大气活性氮含量(μg N/ m3),Ce表示测定的样品浸提液浓度(mg N/L),Cb表示空白浓度(mg N/L),ν表示浸提液体积(mL),V表示一定时间段内采集的大气体积(m3)。

NO2采用英国环境监测网的被动采样器采集。由于本研究对大气NO2浓度进行了1个月的监测,仅在后面的干沉降计算中列出。被动采样器有三部分组成:上下两端的聚乙烯帽(上边为灰色,下边为白色),两层不锈钢网,及中间的丙烯酸管。在两个不锈钢网片加30 μL 20%的三乙醇胺溶液,将两个网片放入灰色聚乙烯帽中,将中间的丙烯酸管插入到灰色加网片的帽中,盖上白色聚乙烯帽,在冰箱中冷藏备用。采样周期为2周,用磺胺、磷酸、NEDA的混合溶液4.2 mL浸提,在542 nm波长下比色测定。

1.3 干沉降的计算方法

干沉降是大气中的气体及颗粒物在相同大气交换机制如:热、湿、及冲量等作用的结果,并强烈的受表面特性:物理、化学、生物等影响的复杂过程[13]。干沉降的研究方法主要有微气象学方法和推算法。涡度相关,梯度等方法对气象参数的测定为干沉降研究的推算模型提供了基础数据。在干沉降推算模型中,干沉降通量用公式[6]为:

F = C*Vd

式中,F表示一定时间段一定面积的氮沉降通量(kg N hm-2 a-1);C为一定高度大气活性氮组分的浓度(μg N /m3); Vd为该种气体的沉降速率(cm /s)。仿照电阻模式,沉降速率可以用公式表示为:

Vd= (Ra+Rb+Rc)-1[6]

式中,Ra代表空气动力学阻力,Rb代表片流层阻力,Rc表示表面阻力或者冠层阻力。其中,RaRb主要是与大气湍流、大气稳定度及气体自身特性决定,该两种参数不确定性相对较小。表面阻力Rc,不同的活性氮种类及不同的下垫面下有不同的计算方法,不确定性较大。本研究没有实测的大气氮干沉降速率的参数,因而采用文献中农田下垫面的沉降速率计算大气氮干沉降量。

1.4 湿沉降的采集

湿沉降的采集采用天津仪器设备厂生产的雨量器收集(SDM6,Tianjin Weather Equipment Inc.,China)。每次降雨发生后用量筒量取体积后,放入冰箱中保存,在一个月内分析测定。无机氮的测定采用上面提到的相同的流动分析仪测定。

1.5 湿沉降的计算

每次降雨氮沉降量(g N/hm2)=降雨量(mm)×NH+4-N/NO-3-N含量(mg N/L)×10。

月或者年氮湿沉降量(kg N/hm2)=0.001×∑ 1月或者1a的氮湿沉降量。

2 结果与分析 2.1 大气活性氮含量

图 1列出了采样期内不同大气活性氮种类的月浓度变化。大气氨气平均含量为5.62 μg N /m3,变化范围为0.88—13.69 μg N /m3。氨气在大气中的含量夏季最高,春季次之,冬季最低。夏季温度较高,又是农作物施肥比较集中的季节,高温导致氨气的挥发量增加,另外,高温还促进氨气其它排放源如:海洋、养殖场、废弃物等的排放[14],导致夏季较高的氨气含量。大气中颗粒态铵平均含量为3.30 μg N /m3,变化范围在0.39—6.49 μg N /m3。颗粒态铵在冬季含量较高,大气硝酸平均含量为0.88 μg N /m3,变化范围为0.11—1.41 μg N /m3。颗粒态硝平均含量2.02 μg N /m3,变化范围为0.19—4.35 μg N /m3。与大气中颗粒态铵季节变化相似,大气颗粒态硝含量也是冬季较高。

图 1 月平均大气活性氮HNO3、pNO-3、NH3和pNH+4含量 Fig. 1 Monthly average atmospheric concentrations of HNO3,pNO-3,NH3,and pNH+4

与国外研究结果相比,本研究的大气活性氮含量整体偏高。欧洲氮项目氮沉降监测网(NitroEurope)大气硝酸浓度为0.03—0.46 μg N /m3,平均值为0.24 μg N /m3[15],颗粒态硝浓度0.02—1.43 μg N /m3,平均值为0.51 μg N /m3,氨气的平均浓度是0.10—7.18 μg N /m3,平均1.96 μg N /m3,颗粒态铵的平均浓度0.12—3.12 μg N /m3,平均浓度是0.69 μg N /m3。美国清洁空气状况与趋势网(Clean Air Status and Trends Network,简称CasTNet)在20世纪90年代的监测表明,各监测点硝酸含量0.10—0.45 μg N /m3,颗粒态硝含量0.05—0.25 μg N /m3,颗粒态铵含量0.22—1.37 μg N /m3[16]。本研究结果大气活性氮浓度大大高于国外的研究结果。而与国内一些地区比,本研究大气活性氮含量又相对偏低。如华北农业区域大气活性氮含量NH3及颗粒铵的含量均高于10 μg N /m3,颗粒态硝的含量也大大高于湛江点[17]

2.2 大气N干沉降估计

由于本研究并无实际测定的各种活性氮组分的干沉降速率,所以选取文献中的沉降速率对大气氮素干沉降量进行估算。表 1总结了国内外一些研究成果对大气氮干沉降速率的直接测定及模型计算。美国大气清洁与趋势网(CasTNet)测定大气活性氮种类包括:颗粒态硝,铵,和气体硝酸,因此大气氮干沉降的速率仅有颗粒态硝、铵、和气体硝酸[16]。本研究与欧洲氮干沉降监测网(NitroEurope)所用仪器相同,因此选用该监测网农田系统的沉降速率估算大气氮素干沉降量。大气NH3、HNO3、NO2、pNO-3、pNH+4的沉降速率分别是0.53、0.8、0.12、0.25、0.25 cm/s[15]。在5种活性氮组分中,硝酸的干沉降速率最高,氨气次之,NO2、pNH+4、和pNO-3干沉降速率最低。

表1 各种活性氮种类在农田的沉降速率 Table 1 Deposition velocities of Nr in cropland
区域AreaNH3/(cm/s)HNO3/(cm/s)NO2/(cm/s)pNO-3/(cm/s)pNH+4/(cm/s)参考文献Reference
n.d. 表示无数据
CasTNetn.d.1.19—1.28n.d.0.10—0.120.10—0.12[16]
NitroEurope0.30—0.750.7—0.90.05—0.200.20—0.300.20—0.30[15]
中国华北0.742.000.590.240.24[17]
江苏0.07—0.23nd0.03—0.13ndnd[18]
福建0.250.810.110.150.15[19]

图 2可以看出,大气氮素干沉降总量为16.41 kg N hm-2 a-1,大气NH3、HNO3、NO2、pNO-3、pNH+4的年沉降量分别为10.13、2.31、1.18、1.65、2.32 kg/hm2。由于仅有一个月的大气NO2浓度(3.30 μg N/m3),因此假定每个月的NO2沉降量相等。从月份看,除1、2、3月份氮干沉降量比较小外,其它月份氮干沉降的数量差别较小。8月氮干沉降总量最大,主要原因是氨气的峰值出现在8月。采样期内,1—3月份大气氨浓度低,虽然颗粒物浓度较高,但颗粒物干沉降速率较低,因此干沉降量较低。氨气在干沉降中的比例最大,其中4—9月半年时间氨的干沉降量占总氮干沉降量的比例超过了50%。

图 2 大气氮干沉降月变化 Fig. 2 Monthly distribution of dry nitrogen deposition
2.3 大气降雨浓度变化及其大气湿沉降

湿沉降与降雨密切相关,不同年份之间差别较大。2010年,采样点降雨量共1952 mm(图 2),高于本地区正常的降雨量。夏季(6,7,8月)月降雨量最多,达到1010.8 mm,超过全年降水量的50%。采样期内,雨水中NO-3的浓度0.39—1.58 mg N/L,NH+4的浓度0.30—2.32 mg N /L,平均浓度分别为0.87、1.11 mg N/L。雨水中无机氮浓度夏季较低,冬季和春季较高,这主要是夏季雨水较多,冬季降雨量少,较高的降雨量对大气中活性氮冲刷以后稀释作用比较明显。大气湿沉降总量为25.3 kg N hm-2 a-1(图 3),其中NH+4-N和NO-3-N的年沉降量分别为13.2、12.0 kg。1年中湿沉降主要发生在4—10月份降雨量比较集中的季节。与国内的一些研究结果相比,本研究大气降雨浓度大大低于华北地区,如Liu[20]研究北京地区雨水NH+4-N浓度范围为3.04—6.50 mg N/L,硝态氮浓度范围为1.60—2.84 mg N/L。大气降雨无机氮浓度与东部及南部的一些研究结果较为接近,如江苏东部降雨中NO-3-N和NH+4-N 浓度分别为1.3和1.3 mg N/L[18]。广州大气降雨无机氮NO-3-N和NH+4-N的浓度分别为0.97和1.20 mg N /L[21]。由于降雨总量较大,虽然降雨中无机氮含量较低,大气湿沉降总量仍然较大。

图 3 采样点无机氮NH+4 和NO-3浓度及月降雨量 Fig. 3 Monthly inorganic N concentrations of NH+4 and NO-3 and monthly rainfall distribution
3 讨论 3.1 采样点大气活性氮来源及影响因素分析

大气NH3的来源主要是畜禽养殖及氮肥施用导致的氨挥发损失。本研究采样点周围的氮肥施肥时期集中于每年的5—10月,对应的5—10月大气NH3浓度较高(图 1),而在冬季非施肥季大气NH3浓度较低,说明采样点大气NH3浓度主要来源于氮肥施用(在一些NH3排放较为复杂的地区NH3在大气中的背景浓度很高,即便是冬天大气NH3浓度也可达6 μg N/m3[22])。在采样期内大气NH3浓度和温度呈显著相关(图 5)(采样期温度数据来自www.wunderground.com),因此大气NH3浓度夏季较高,与施肥期基本同步,这与华北地区及太湖地区的研究具有可比性[17, 18]。大气HNO3来源于氮氧化物在大气中的转化,由于其在大气中浓度差别不大,季节变化并不明显,采用瞬时的研究表明,大气HNO3浓度的峰值往往出现在一天的中午[23]。颗粒态NH+4来源于大气NH3与酸性气体(H2SO4,HNO3)的反应,除了受反应物浓度影响外,还受气象条件如温度,相对湿度等的影响[24],在夏季富NH3条件下有利于颗粒态NH+4的形成,然而在夏季多雨的条件下,夏季颗粒态NH+4浓度并不高。颗粒态NO-3来源于大气中氮氧化物的转化,高浓度值大多出现在较为干燥的冬季[17]。颗粒态NH+4和颗粒态NO-3是大气颗粒物的重要组成部分,中国的大气颗粒物组成整体上有北方高于南方的趋势[25],这与本研究的结果较为一致,本研究大气颗粒态NH+4和NO-3的浓度分别为3.30 μg N /m3和2.02 μg N /m3,大大低于本小组在北方地区的监测结果(大气pNH+4和pNO-3浓度分别为8.4 μg N /m3和4.6 μg N /m3[22])。雷州半岛地区不是我国主要的集约化粮食主产区,区内以热带经济作物为主,虽然经济作物的施氮量也很高(平均约400 kg N hm-2 a-1),但是大气NHx(NH3+pNH+4)浓度较低,可能是该地区土壤pH值很低,会降低土壤的氨挥发潜力[26]。同时,该地区降雨量大,地表草地和森林覆盖度高,又濒临海洋,受大陆或者海洋风作用明显,有利于污染物的扩散。

图 4 采样点月湿沉降量 Fig. 4 Monthly wet nitrogen deposition
图 5 大气NH3浓度与温度的相关关系 Fig. 5 Correlations between atmospheric NH3 concentration and temperature **表示在0.01水平上显著相关
3.2 大气氮干沉降的不确定性分析

大气氮干沉降包括的活性氮种类较多,主要包括气体NH3、HNO3、NO2及颗粒态NO-3,NH+4及有机氮。在目前经典的计算干沉降的方法中,确定干沉降速率又是其中的难点。不同气体及颗粒物之间由于不同的性质,大气氮干沉降速率也有很大差别。影响气体NH3、HNO3、NO2的3种阻力参数中,空气动力学阻力,片流层阻力差别较小,而表面阻力差别较大,如在多数的沉降模型中,HNO3的表面阻力大多假定为零,NO2和NH3 存在植物和大气之间的交换,通常用补偿点的理论解释植物对两者的吸收或者排放。所以对NH3及NO2沉降的计算还存在一定的不确定性。颗粒物的沉降与气体的沉降又有差别,其主要受布朗扩撒,惯性碰撞和重力沉降等因素影响,离子沉积到表面后通常认为没有再悬浮,表面阻力可以忽略[27]。从表 1可以看出,各种报道中对颗粒物NH+4和NO-3的沉降速率较为接近,因此对颗粒物硝,铵干沉降的计算不确定性并不是很大。

3.3 本研究不同组分对大气氮沉降的贡献及与一些地区的比较

大气氮沉降,包括湿沉降和干沉降,国内对大气湿沉降研究较多,而干沉降的研究相对较少[17]。大气氮干沉降的不确定性较大,但是它是大气氮沉降的重要组成部分,其在欧洲占氮沉降量的10%—90%[28]。本研究显示,湿沉降NH+4-N,NO-3-N及干沉降NH3、HNO3、NO2、 pNH+4、pNO-3分别占沉降量的30.8%、28.0%、23.7%、5.4%、2.8%、3.9%、5.4%,干沉降占总沉降量的41.2%。中国不同区域由于活性氮排放强度不同,大气氮沉降存在一定差别,华北地区大气活性氮污染严重,大气氮沉降量大,在六个采样点的研究显示,大气氮沉降总量为54.4—103.2 kg N hm-2 a-1,其中干沉降量为35.2—60.0 kg N hm-2 a-1,城市采样点大气氮沉降显著高于农村[22]。邻近本研究采样点广东肇庆森林采样点大气湿沉降量为16.2—38.2 kg N hm-2 a-1[11]。浙江农田区域年氮湿沉降量为18—32 kg/hm2[29]; 湖南亚热带地区森林,农田的大气氮沉降 (包括干沉降和湿沉降)为22—55 kg N hm-2 a-1[30]。南方城市采样点大气氮湿沉降也较高,如上海和广州大气湿沉降量也可达40.5和58.1 kg N hm-2 a-1[31]

本研究表明,雷州半岛典型农田大气氮沉降总量达42.9 kg N hm-2 a-1,作为氮平衡的一部分,该部分的养分输入需要在农田生态系统得到考虑。大气氮沉降超过10 kg N hm-2 a-1就会降低森林的物种多样性[1]。氮沉降通过径流及土壤侵蚀汇入河流会导致水体的富营养化[29]。因此,氮沉降对周边森林、草地、水体的环境影响值得关注。

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