流域人类活动净氮输入量的估算、不确定性及影响因素

人类活动使得大量的氮素进入流域生态系统,大量氮的盈余导致了一系列生态环境问题的出现。为了评估人类活动对流域生态系统的影响,Howarth等于1996年提出了人类活动净氮输入(NANI)的概念。综述了当前人类活动净氮输入的估算方法、不确定性及影响因素,并得到以下结论:导致NANI估算结果的不确定性原因主要有:内涵分歧、数据来源、尺度转换、估算方法的分歧。影响NANI的主要因素包括:各输入项、人口密度、土地利用组成;对于各输入项而言,化肥施用是最主要的氮素输入来源,占人类活动净氮输入总量的79.0%,其次为作物固氮,占17.6%,食品/饲料氮净输入量占-14.5%,大气沉降占15.7%;对于人口密度,NANI随着人口密度的增大而增大,当人口密度高于100人/km2,人口密度对NANI的影响趋于稳定,其他因素起主导作用。对于土地利用组成:NANI与森林面积比例成负相关,而与耕地面积比例成正相关。     

1990-2010年淮河流域人类活动净氮输入

1990-2010年,淮河流域粮食产量由6414× 104 t增长到10121×104 t(增幅为58％),城市化率由13％增长到35％(涨幅为22％),流域社会经济发生了显著变化.从流域整体定量评估人类活动所带来的生态环境影响将为区域生态环境管理提供科学依据.本文估算淮河流域1990-2010年人类活动净氮输入(NANI)的空间分布及变化趋势.结果表明:研究期间,淮河流域氮输入量呈现出增加趋势;1990-2001年流域内氮输入量快速增加,2001年后氮输入增加趋势减缓.1990年氮输入量为17232 kg N·km-2·a-1,2003年氮输入量最高,为28771kgN·km-2· a-1,2010年回落为26415 kg N·km-2·a-1.从氮输入的组成上来看,化肥和大气氮沉降仍然是最主要的输入来源,其次为食品/饲料和生物固氮的输入.化肥和大气沉降输入占总氮输入的比例持续增加,由1990年的64％和16％分别增长至2010年的77％和19％.单纯以增施化肥来实现粮食增产、化石燃料大量燃烧来推动经济发展的观念,应切实转变到改善农业耕种技术、实现新能源的发展轨道上来,进而推动社会经济的可持续发展.     

1990—2010年淮河流域人类活动净氮输入

1990—2010年,淮河流域粮食产量由6414×10⁴ t增长到10121×10⁴ t(增幅为58%),城市化率由13%增长到35%(涨幅为22%),流域社会经济发生了显著变化.从流域整体定量评估人类活动所带来的生态环境影响将为区域生态环境管理提供科学依据.本文估算淮河流域1990—2010年人类活动净氮输入(NANI)的空间分布及变化趋势.结果表明: 研究期间,淮河流域氮输入量呈现出增加趋势;1990—2001年流域内氮输入量快速增加,2001年后氮输入增加趋势减缓.1990年氮输入量为17232 kg N·km^-2·a^-1,2003年氮输入量最高,为28771 kg N·km^-2·a^-1,2010年回落为26415 kg N·km^-2·a^-1.从氮输入的组成上来看,化肥和大气氮沉降仍然是最主要的输入来源,其次为食品/饲料和生物固氮的输入.化肥和大气沉降输入占总氮输入的比例持续增加,由1990年的64%和16%分别增长至2010年的77%和19%.单纯以增施化肥来实现粮食增产、化石燃料大量燃烧来推动经济发展的观念,应切实转变到改善农业耕种技术、实现新能源的发展轨道上来,进而推动社会经济的可持续发展.     

江苏省稻纵卷叶螟迁入期虫情指标与西太平洋海温的遥相关及其长期预报模型

将西太平洋海温作为长期预报因子,根据场相关分析方法进行相关普查,用GRADS软件绘制了江苏省宜兴、盐都、靖江地区稻纵卷叶螟迁入峰期、峰期持续时间及峰期蛾量等各虫情指标与各格点逐月的月海温值间相关系数的时、空分布图,从中找出了与稻纵卷叶螟迁入期各虫情指标相关的强信号海区,并对预测因子进行最优化相关处理,建立了三地区稻纵卷叶螟迁入期各虫情指标的长期预报模型.结果表明：三地区稻纵卷叶螟迁入峰期与西太平洋海温存在共同的高相关区;稻纵卷叶螟迁入持续时间与西太平洋海温具有较好的相关关系;海温显著影响迁入峰期蛾量,二者间具有较稳定的相关关系,且其相关程度随季节变化而变化;所有预报模型均通过了α＝0.01的显著性水平检验,说明预报结果与实际值较吻合,预报模型切实可行.该预报模型将能提前1~2个月做出预测意见,对江苏省水稻虫害防治、水稻生产以及最大限度地减轻化学农药污染、改善环境质量具有重要意义.     

北京市妫水河流域人类活动的水文响应

选取1986-1987年、2005-2006年为两个研究时段,解译1987年和2005年两幅土地利用图,分析土地利用和气候变化情况.利用土壤水评价模型(Soil Water Assessment Tool,SWAT)量化近20年来人类活动对妫水河流域产生的直接与间接影响.结果显示:人类活动的间接影响使径流量增加,汛期(6-8月)增加显著,增幅达34.67％.另外,涨水与退水过程明显加快,径流分配趋于不均匀.人类活动的直接影响使径流量大幅度降低,平均径流系数下降了87％以上.涨水和退水过程基本消失,径流量分配趋于均匀.因此,在妫水河流域,人类活动的间接影响使流域涵养水源能力下降,易发生洪涝和干旱.人类活动的直接影响增加了降水的利用率,减少了洪涝和干旱.     

定量评价人类活动对净初级生产力的影响

以人类活动为主导的城市扩张和土地覆被变化对城市生态环境产生了重要影响,并与气候变化共同影响植被净初级生产力(NPP),但目前从时空尺度上脱离气候干扰仅以人类活动为主导因素来定量分析其对植被NPP影响的研究尚不充分.本研究以广州市为研究区,利用CASA模型估算2001—2013年实际净初级生产力(NPP_act),结合CHIKUGO模型估算得到的潜在净初级生产力(NPP_p)计算因土地覆被变化导致的NPP损失(NPP_lulc),并建立相对贡献指数(RCI)定量分析和评价在城市扩张过程中人类活动对NPP的影响.结果表明:2001—2013年间,广州总体及其5片区NPP_act和NPP_lulc分别呈减少和增加趋势,并存在明显的空间差异性;RCI呈明显增加趋势,东北片区RCI值最低,为0.31,表明气候变化是其NPP变化的主要原因,其他4个片区的RCI值均高于0.5,说明4个片区人为干扰严重,人类活动是其NPP减少的主导因素;广州市及其5片区的RCI变化斜率均大于0,人类活动对植被的干扰逐年增强,北部片区RCI变化斜率值最大(0.693),人为干扰增加趋势最明显.     

洞庭湖流域人类活动净磷输入及其空间分布

本研究基于人类活动净磷输入模型(NAPI)估算了1985、1995、2005和2015年洞庭湖流域及其子流域磷元素的输入特征,并分析其时空分布及变化趋势.结果表明:过去30年洞庭湖流域NAPI呈现先升高后降低的趋势,1985、1995、2005、2015年流域NAPI分别为7.00、9.20、10.33、10.01 kg·hm^-2·a^-1.从磷的组成来年,1985年最大的输入源为食品/饲料净输入,1995-2015年NAPI最大输入源为磷肥施用.磷肥输入年均值为6.01 kg·hm^-2·a^-1,占NAPI年均值的65.8%;其次是食品/饲料磷净输入,年均值为2.65 kg·hm^-2·a^-1,占比为29.0%;非食品磷输入年均值为0.47 kg·hm^-2·a^-1,占比为5.2%.从空间分布上,洞庭湖流域的较高的NAPI主要分布在东北部,与该区域农业的相对集中分布有关.从子流域NAPI组成上,洞庭湖子流域的NAPI总体均呈现逐年上升的趋势,各流域年均NAPI强度从高到低依次为:洞庭湖环湖区>湘江下游>资江上游>湘江上游>澧水>沅江上游>沅江下游>资江下游.洞庭湖环湖区是子流域中NAPI最高的区域,1985年NAPI为13.01 kg·hm^-2·a^-1,2015年上升至24.14 kg·hm^-2·a^-1.农业生产和人口增长是导致当前人类活动净磷输入的主要原因,其带来的负面生态效应是不容忽视的.     

疏勒河流域气候变化和人类活动对植被NPP的相对影响评价

气候变化和人类活动是对陆地生态系统碳循环产生重要影响的两个因素,定量评估气候变化与人类活动对植被净初级生产力(NPP)的相对影响,对深入理解其驱动机制和控制荒漠化发展具有重要意义。以疏勒河流域为研究区,利用遥感和气象数据计算潜在NPP(PNPP)及其与实际NPP(ANPP)之间的差值,分别衡量了气候变化和人类活动对流域NPP的相对影响。研究结果表明:(1)2001—2015年疏勒河流域年ANPP整体呈缓慢增加趋势,与全国和西北地区相比,普遍较低,流域植被整体生产力水平不高。流域年ANPP空间分布呈现上游祁连山区和中下游绿洲区ANPP较高,而中下游荒漠戈壁区ANPP较低的分布格局。(2)2001—2015年流域年PNPP的变化趋势表明,降水量的变化是导致疏勒河流域植被退化加剧或缓解的主要气候驱动因素,但气温的变化对植被的影响较为复杂。(3)2001—2015年流域大部分地区植被退化系人类活动造成的,但人类活动的负向影响力在减弱。(4)气候变化和人类活动对植被NPP的相对影响均表现出明显的空间异质性,其中人类活动是疏勒河流域植被变化的主要驱动因素。     

高寒生态系统脆弱性及其对气候变化和人类活动的响应

了解陆地生态系统的脆弱性和基本机制是适应和减轻全球气候变化影响的决策基础。生态系统的脆弱性可以通过生产力对气候变化的敏感性和适应性进行量化。采用1982-2018年青海省境内基于遥感的现实净初级生产力（NPP_R）和气候驱动的潜在净初级生产力（NPP_C）,量化了高寒生态系统的敏感性（Sensitivity）、适应性（Adaptability）和脆弱性（Vulnerability）。然后探讨了生态系统脆弱性的时空变化,并分别从人类活动和气候变化的影响方面分析了其基本机制。结果表明：（1）基于NPP_R和NPP_C的生态系统脆弱性在空间上呈现出中度脆弱的模式,脆弱性从东南向西北由不脆弱依次递增到极度脆弱等级。（2）耕地的脆弱性较低,基于NPP_R和NPP_C的指数分别为-1.31和-0.93,这是由于其适应水平较高而敏感性较低;森林次之,指数为-1.18（NPP_R）和-1.06（NPP_C）;草原的指数为-0.17（NPP_R）和-0.17（NPP_C）;而荒漠的脆弱性较高,指数为0.77（NPP_R）和0.78（NPP_C）,这是由于其敏感性较高,适应性较低。（3）基于NPP_R的高寒草地的脆弱性有两个温度阈值（-2.2±0.8）℃和（5.5±0.8）℃,一个降水阈值（387±45.6）mm,两个干旱指数阈值为（14.2±20.2）和（78.2±20.2）。而基于NPP_C的脆弱性也发现了同样的阈值,并且数值相似。阈值表明最佳气候条件下,生态系统将具有较高的适应性和较低的敏感性,即较低的脆弱性。但如果气温较低或较高,或者降水较低,生态系统的脆弱性将会更高。（4）人类活动对东部地区生态系统的脆弱性产生了强烈的影响,但就整个青海省的生态系统而言,这些影响在区域平均水平上较小。这项研究表明,在高寒脆弱的生态系统中,气候条件决定了脆弱性在空间上的分布情况,这应该被视为生态保护决策的理论基础。此外,本研究发现的阈值将为生态系统生态学提供一个案例研究,并应在世界各地的脆弱生态系统中广泛探索。     

藏北高寒草地NPP变化趋势及其对人类活动的响应

基于1981～2004年多年遥感监测数据和气象数据以及其它相关数据,采用CASA(Carnegie-Ames-Stanford Approach)模型估算藏北地区草地植被净第一性生产力(NPP),分析草地植被NPP变化趋势的空间格局及其对人类活动强度的响应。结果表明:近24a以来,藏北绝大部分区域(约占草地总面积的88.61%)草地植被NPP变化趋势不明显;而草地植被NPP变化趋势显著的区域仅占草地总面积的11.39%,其中显著降低约占11.30%,显著增高仅占0.09%。在藏北地区,高海拔区域有较大比例(大于26%)的草地NPP显著降低;坡度在15～30°之间区域的草地NPP变化幅度较大;而坡向对草地NPP变化趋势的影响不大。藏北地区居民点对草地NPP变化趋势的负面影响小于道路影响;从综合影响来看,离道路和居民点越近、人类活动强度及其对草地NPP变化趋势的影响越大,尤其是草地NPP显著增高区域只分布在人类活动强度最大的第一个缓冲区内。     

Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern U.S.A.

Human activities have greatly altered the nitrogen (N) cycle, accelerating the rate of N fixation in landscapes and delivery of N to water bodies. To examine relationships between anthropogenic N inputs and riverine N export, we constructed budgets describing N inputs and losses for 16 catchments, which encompass a range of climatic variability and are major drainages to the coast of the North Atlantic Ocean along a latitudinal profile from Maine to Virginia. Using data from the early 1990's, we quantified inputs of N to each catchment from atmospheric deposition, application of nitrogenous fertilizers, biological nitrogen fixation, and import of N in agricultural products (food and feed). We compared these inputs with N losses from the system in riverine export.The importance of the relative sources varies widely by catchment and is related to land use. Net atmospheric deposition was the largest N source (>60%) to the forested basins of northern New England (e.g. Penobscot and Kennebec); net import of N in food was the largest source of N to the more populated regions of southern New England (e.g. Charles & Blackstone); and agricultural inputs were the dominant N sources in the Mid-Atlantic region (e.g. Schuylkill & Potomac). Over the combined area of the catchments, net atmospheric deposition was the largest single source input (31%), followed by net imports of N in food and feed (25%), fixation in agricultural lands (24%), fertilizer use (15%), and fixation in forests (5%). The combined effect of fertilizer use, fixation in crop lands, and animal feed imports makes agriculture the largest overall source of N. Riverine export of N is well correlated with N inputs, but it accounts for only a fraction (25%) of the total N inputs. This work provides an understanding of the sources of N in landscapes, and highlights how human activities impact N cycling in the northeast region.     

Responses of tree and insect herbivores to elevated nitrogen inputs: A meta-analysis

Increasing atmospheric nitrogen (N) inputs have the potential to alter terrestrial ecosystem function through impacts on plant-herbivore interactions. The goal of our study is to search for a general pattern in responses of tree characteristics important for herbivores and insect herbivorous performance to elevated N inputs. We conducted a meta-analysis based on 109 papers describing impacts of nitrogen inputs on tree characteristics and 16 papers on insect performance. The differences in plant characteristics and insect performance between broadleaves and conifers were also explored. Tree aboveground biomass, leaf biomass and leaf N concentration significantly increased under elevated N inputs. Elevated N inputs had no significantly overall effect on concentrations of phenolic compounds and lignin but adversely affected tannin, as defensive chemicals for insect herbivores. Additionally, the overall effect of insect herbivore performance (including development time, insect biomass, relative growth rate, and so on) was significantly increased by elevated N inputs. According to the inconsistent responses between broadleaves and conifers, broadleaves would be more likely to increase growth by light interception and photosynthesis rather than producing more defensive chemicals to elevated N inputs by comparison with conifers. Moreover, the overall carbohydrate concentration was significantly reduced by 13.12% in broadleaves while increased slightly in conifers. The overall tannin concentration decreased significantly by 39.21% in broadleaves but a 5.8% decrease in conifers was not significant. The results of the analysis indicated that elevated N inputs would provide more food sources and ameliorate tree palatability for insects, while the resistance of trees against their insect herbivores was weakened, especially for broadleaves. Thus, global forest insect pest problems would be aggravated by elevated N inputs. As N inputs continue to rise in the future, forest ecosystem management should pay more attention to insect pest, especially in the regions dominated by broadleaves.     

Bryophytes attenuate anthropogenic nitrogen inputs in boreal forests

Productivity in boreal ecosystems is primarily limited by available soil nitrogen (N), and there is substantial interest in understanding whether deposition of anthropogenically derived reactive nitrogen (N_r) results in greater N availability to woody vegetation, which could result in greater carbon (C) sequestration. One factor that may limit the acquisition of N_r by woody plants is the presence of bryophytes, which are a significant C and N pool, and a location where associative cyanobacterial N‐fixation occurs. Using a replicated stand‐scale N‐addition experiment (five levels: 0, 3, 6, 12, and 50 kg N ha^?1 yr^?1; n=6) in the boreal zone of northern Sweden, we tested the hypothesis that sequestration of N_r into bryophyte tissues, and downregulation of N‐fixation would attenuate N_r inputs, and thereby limit anthropogenic N_r acquisition by woody plants. Our data showed that N‐fixation per unit moss mass and per unit area sharply decreased with increasing N addition. Additionally, the tissue N concentrations of Pleuorzium schreberi increased and its biomass decreased with increasing N addition. This response to increasing N addition caused the P. schreberi N pool to be stable at all but the highest N addition rate, where it significantly decreased. The combined effects of changed N‐fixation and P. schreberi biomass N accounted for 56.7% of cumulative N_r additions at the lowest N_r addition rate, but only a minor fraction for all other treatments. This ‘bryophyte effect’ can in part explain why soil inorganic N availability and acquisition by woody plants (indicated by their δ¹⁵N signatures) remained unchanged up to N addition rates of 12 kg ha^?1 yr^?1 or greater. Finally, we demonstrate that approximately 71.8% of the boreal forest experiences N_r deposition rates at or below 3 kg ha^?1 yr^?1, suggesting that bryophytes likely limit woody plant acquisition of ambient anthropogenic N_r inputs throughout a majority of the boreal forest.     

Prorocentrum minimum tracks anthropogenic nitrogen and phosphorus inputs on a global basis: Application of spatially explicit nutrient export models

Nutrient over-enrichment from land-based sources has degraded estuarine and coastal marine waters worldwide. Linking nutrient loading, in magnitude and form, to specific ecosystem effects, however, has been a challenge on the global scale. The harmful algal species Prorocentrum minimum has long been thought to be associated with eutrophication based on several site-specific long-term databases and a previous review of its global spreading. Using recently developed spatially explicit models that quantify global river nitrogen (N) and phosphorus (P) export to the coastal zone and the contribution of natural and anthropogenic sources, as well as a review of the global distribution of P. minimum, we show that this HAB species is associated with regions of high dissolved inorganic nitrogen (DIN) and phosphorus (DIP) exports that are strongly influenced by anthropogenic sources (such as fertilizers and manures for DIN). Blooms of this species were also linked to regions with relatively high anthropogenic contributions to dissolved organic N and P export. The global distribution of this species is expected to expand, given that nutrient inputs to watersheds from agriculture, sewage and fossil fuel combustion are projected to more than double by 2050 unless technological advances and policy changes are implemented.     

Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs

We present the first estimates of net anthropogenic nitrogen input (NANI) in European boreal catchments. In Swedish catchments, nitrogen (N) deposition is a major N input (31–94%). Hence, we used two different N deposition inputs to calculate NANI for 36 major Swedish catchments. The relationship between riverine N export and NANI was strongest when using only oxidized deposition (NO_y) as atmospheric input (r² = 0.70) rather than total deposition (i.e., both oxidized and reduced nitrogen, NO_y + NH_x deposition, r² = 0.62). The y-intercept (NANI = 0) for the NANI calculated with NO_y is significantly different from zero (p = 0.0042*) and indicates a background flux from the catchment of some 100 kg N km^?2 year^?1 in addition to anthropogenic inputs. This agrees with similar results from North American boreal catchments. The slope of the linear regressions was 0.25 for both N deposition inputs (NO_y and NO_y + NH_x), suggesting that on average, 25% of the anthropogenic N inputs is exported by rivers to the Baltic Sea. Agricultural catchments in central and southern Sweden have increased their riverine N export up to tenfold compared to the inferred background flux. Although the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition, these catchments do not show significantly elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention may be saturating as loading rates increase. In northern and western Sweden the export of nitrogen is largely controlled by the hydraulic load, i.e., the riverine discharge normalized by water surface area, which has units of distance time^?1. Besides hydraulic load the percent total forest cover also affects the nitrogen export primarily in the northern and western catchments.     

Watershed nitrogen input and riverine export on the west coast of the US

This study evaluated the sources, sinks, and factors controlling net export of nitrogen (N) from watersheds on the west coast of the US. We calculated input of new N to 22 watersheds for 1992 and 2002. 1992 inputs ranged from 541 to 11,644 kg N km⁻² year⁻¹, with an overall area-weighted average of 1,870 kg N km⁻² year⁻¹. In 2002, the range of inputs was 490–10,875 kg N km⁻² year⁻¹, averaging 2,158 kg N km⁻² year⁻¹. Fertilizer was the most important source of new N, averaging 956 (1992) and 1,073 kg N km⁻² year⁻¹ (2002). Atmospheric deposition was the next most important input, averaging 833 (1992) and 717 kg N km⁻² year⁻¹ (2002), followed by biological N fixation in agricultural lands. Riverine N export, calculated based on measurements taken at the furthest downstream USGS water quality monitoring station, averaged 165 (1992) and 196 kg N km⁻² year⁻¹ (2002), although data were available for only 7 watersheds at the latter time point. Downstream riverine N export was correlated with variations in streamflow (export = 0.94 × streamflow − 5.65, R ² = 0.66), with N inputs explaining an additional 16% of the variance (export = 1.06 × streamflow + 0.06 × input − 227.78, R ² = 0.82). The percentage of N input that is exported averaged 12%. Percent export was also related to streamflow (%export = 0.05 × streamflow − 2.61, R ² = 0.60). The correlations with streamflow are likely a result of its large dynamic range in these systems. However, the processes that control watershed N export are not yet completely understood.     

森林土壤微生物对干旱和氮沉降的响应

干旱和氮沉降深刻影响着人类世森林生态系统的生命活动与物质循环,进而影响全球碳平衡、并反馈作用于气候变化。土壤微生物驱动元素的生物地球化学循环和关键土壤生态过程,在气候变化生物学研究方面具有核心地位和全球重要性。本文综述了干旱和氮沉降对森林土壤细菌和菌根真菌的影响。提出未来应加强全球变化多因子交互作用对土壤微生物多样性、活性与生态功能的研究;建立野外长期定位站,强化亚热带森林生态系统与全球变化研究;注重土壤生物之间互作及网络研究;利用微生物大数据建立相关的机理模型等。从认识微生物多样性和群落组成对全球变化的响应与适应,逐步发展为调控利用微生物群落服务于森林的优化管理、生态资源的合理保护与可持续利用,为充分发挥微生物减缓全球气候变化的作用提供理论基础。