陆地生态系统氮状态对碳循环的限制作用研究进展

陆地生态系统碳循环和氮循环密切相关, 碳贮量与碳通量在很大程度上受氮循环的影响 和限制。由于氮循环的复杂性, 在以往的大多数碳循环研究中, 更多考虑水分、温度和大气CO2 浓 度等因子的影响, 考虑碳氮相互作用的研究较少。氮素可限制植物光合、有机质分解、同化产物的 分配以及生态系统对大气CO2 浓度升高的响应。根据目前有关碳氮模型的发展状况可将碳氮耦 合循环模型分为三大类: 一是静态模型, 它的土壤养分水平或者叶氮含量不变, 是常数, 这类模型 适合于在站点或氮素浓度变化不大的区域应用; 二是土壤氮限制模型, 能够保持稳定的生态系统 氮收支, 在NPP(Net Primary Productivity, 净初级生产力)的模拟中考虑土壤氮有效性的动态变化 的影响, 使模拟结果更为合理; 三是叶氮限制模型, 在NPP 的模拟中考虑叶片氮浓度的动态变化 的影响。这三类模型虽然都考虑了氮对碳循环的限制作用, 但在氮碳循环机理方面尚有不少欠 缺, 所以在研究中可能会带来很大的不确定性。在以后的研究中, 应通过加强碳氮相互作用的实 验研究, 增进对碳氮过程的深入了解, 进而建立综合动态的碳氮耦合模型, 以减少目前碳循环研 究中的不确定性。     

北极快速变化的生态环境响应

北冰洋由于其特殊的地理位置,成为全球变化响应最为敏感的地区。本文聚焦北极海冰变化幅度最大的西北冰洋,从营养盐、叶绿素、浮游植物群落和沉积碳埋藏等变化来讨论海洋生态环境对北极快速变化的响应。尽管太平洋北向流和北极周边河流输入加强可以增加西北冰洋上层营养盐储库,但由于夏季硅藻旺发向沉积物迁出大量生源元素,使得上层营养盐相对亏损,部分海域存在显著的氮限制和硅限制。随海冰减退,尽管夏末海盆区浮游植物呈现小型化趋势,但西北冰洋总体上浮游植物现存量和初级生产力呈现增高的趋势;伴随叶绿素极大层下移、北扩,以硅藻为代表的生物泵过程得以更高效的运转。在沉积物埋藏的有机碳中,除原先北冰洋生态系统占据重要比份的冰藻外,硅藻等藻类的有机碳埋藏也逐渐增加。西北冰洋海洋初级生产力的增加不仅促进了生物泵的运转和碳的埋藏,而且给海洋生态系统提供了更多的食物来源。北极海域目前已成为全球碳源汇格局变化最大、海洋生态系统改变最显著的地区之一。     

A Review of “Renewable Energy Project Development Under the Clean Development Mechanism: A Guide for Latin America”

Books reviewed in this article:

Kurt E. Engelmann and Vjeran Pavlakovic (eds.), Rural Development in Eurasia and the Middle East: Land Reform, Demographic Change, and Environmental Constraints

Gregory C. Randall, America's Original GI Town: Park Forest, Illinois

John B. Rehder, Delta Sugar: Louisiana's Vanishing Plantation Landscape

Cathy D. Knepper, Greenbelt, Maryland: A Living Legacy of the New Deal

Char Miller (ed.), Fluid Arguments: Five Centuries of Western Water Conflict

Edward F. Bergman, The Spiritual Traveler: New York City: The Guide to Sacred Spaces and Peaceful Places

Rachel Pain, Michael Barke, Duncan Fuller, Jamie Gough, Robert MacFarlane, and Graham Mowl, Introducing Social Geographies

Tor A. Benjaminsen, and Christian Lund, (eds.), Politics, Property, and Production in the West African Sahel: Understanding Natural Resources Management

Al Gedicks, Resource Rebels: Native Challenges to Mining and Oil Corporations

Maryann P. Feldman and Nadine Massard (eds.), Institutions and Systems in the Geography of Innovation

Richard Foglesong, Married to the Mouse: Walt Disney World and Orlando

Annick Germain, and Damaris Rose, Montréal: The Quest for a Metropolis

George F. Rengert, Mark T. Mattson, and Kristin D. Henderson, Campus Security: Situational Crime Prevention in High–Density Environments

Vaclav Smil, Feeding the World: A Challenge for the Twenty–First Century

Pu Miao (ed.), Public Places in Asia Pacific Cities: Current Issues and Strategies

Lisa M. Benton and John Rennie Short (eds.), Environmental Discourse and Practice: A Reader

Philip Scranton (ed.), The Second Wave: Southern Industrialization from the 1940s to the 1970s

Barry Dalal–Clayton and David Dent, Knowledge of the Land: Land Resources Information and Its Use in Rural Development     

2014年5月8—9日引发珠江口区域强降水的两个长生命史MCS特征分析

2014年5月8日上午至9日白天,广东中南部珠江口地区连续受MCS A1、MCS A2两个长生命史中尺度对流系统影响,形成长时间强降水。其中5月8日午后华南内陆地区MCS A1逐步增强,从广西东部向广东珠江口方向移动,陆上活动时间超过11 h; MCS A2从9日凌晨至上午持续影响珠江口沿海地区,维持时间超过9 h,导致珠江口沿海地区出现400 mm 以上单站降水量。过程发生前,8日早上华南南部地区具有弱地面温度梯度,中午MCS A1对流触发与广西南部地面南风增强、华南南部云开大山—云雾山中尺度地形抬升有紧密关系;在弱斜压环境条件下,MCS A1从层云伴随线状对流结构演变为中尺度涡旋组织结构。8日夜间MCS S1入海后,与陆上遗留冷池相关的地面温度边界稳定在珠江口西侧沿海地区;9日凌晨西南低空急流增强后,MCS A2在珠江口沿海残留冷池边界附近开始发展,在向上游迎风方向传播的过程中,逐步形成多条平行β中尺度线状对流组织结构,对流系统整体移动缓慢,造成珠江口沿海地区出现较高的总降水量。计算表明MCS A2冷池边界扩张速度与低层垂直切变相对平衡,有利于形成较为直立的对流单体,增强的边界层水汽输送、更高的对流单体高度有利于产生较高的降水强度。通过总结这两个华南地区长生命史MCS发生发展过程,表明通过分析对流反馈造成的边界层/近地面层热动力特征变化,对于分析MCS发展特征、提高华南前汛期中尺度暴雨预报能力具有重要意义。     

Variability of Nonionellina labradorica Dawson in Surface Sediments from Kongsfjorden, West Spitsbergen

Kongsfjorden is a fjord in Spitsbergen (Svalbard archipelago) that lies adjacent to both Arctic and Atlantic water masses and is therefore a suitable site to understand the effects of climate change on ecosystems. To decipher the effect of the lateral advection of transformed Atlantic water (TAW) within the fjord, spatial variations of foraminiferal tests, their test size variations and stable isotopic composition (δ13C and δ18O) in the surface sediments were studied. Total organic carbon and textural analyses were also carried out. The dominant benthic foraminifera included Nonionellina labradorica, Elphidium excavatum, Cassidulina reniforme, Quinqueloculina stalkeri and Islandiella islandica. Nonionellina labradorica was the predominant species in the outer fjord, whereas Elphidium excavatum and Cassidulina reniforme were dominant in the inner fjord. Total organic carbon and the test size of Nonionellina labradorica within the fjord were highly correlated (r2?=?0.97) and both showed a decreasing trend towards the inner fjord. Based on the distribution and abundance of Nonionellina labradorica as well as temperature profiles, we suggest that there was little or no major change in the lateral advection of TAW within the fjord in the immediate past.     

中国森林乔木林碳储量及其固碳潜力预测

加强对我国森林碳储量和固碳潜力的研究,是制定中国增汇减排政策的重要依据,对我国国际气候谈判和全面了解森林碳汇潜力具有重要作用。利用我国第七次和第八次森林资源清查中各优势树种的面积和蓄积量数据,采用IPCC材积源生物量法（volume-biomass method),估算了我国森林（乔木林）碳储量和碳密度及其分布,分析我国不同省份天然乔木林和人工乔木林碳储量龄组结构特征;建立分区域、分起源主要优势树种的单位面积蓄积-林龄Logistic生长方程,结合我国森林2020年和2030年面积蓄积增长目标,预测我国乔木林2010—2050年间碳汇潜力。结果表明：第八次清查期间中国乔木林总碳储量为6135.68 Tg,碳密度为37.28 Mg/hm ²;天然乔木林和人工乔木林的碳储量分别为5246.07 Tg和889.61 Tg,分别占总碳储量的85.50%和14.50%。到2050年,中国乔木林和新造林的总碳储量和平均碳密度将分别达到11125.76 Tg和52.52 Mg/hm ²,与2010年相比分别增加81%和41%。分析结果表明中国乔木林有很大的碳汇潜力,将在应对和减缓全球气候变化中发挥重要作用。     

Modeling forced pool–riffle hydraulics in a boulder-bed stream, southern California

The mechanisms which control the formation and maintenance of pool–riffles are fundamental aspects of channel form and process. Most of the previous investigations on pool–riffle sequences have focused on alluvial rivers, and relatively few exist on the maintenance of these bedforms in boulder-bed channels. Here, we use a high-resolution two-dimensional flow model to investigate the interactions among large roughness elements, channel hydraulics, and the maintenance of a forced pool–riffle sequence in a boulder-bed stream. Model output indicates that at low discharge, a peak zone of shear stress and velocity occurs over the riffle. At or near bankfull discharge, the peak in velocity and shear stress is found at the pool head because of strong flow convergence created by large roughness elements. The strength of flow convergence is enhanced during model simulations of bankfull flow, resulting in a narrow, high velocity core that is translated through the pool head and pool center. The jet is strengthened by a backwater effect upstream of the constriction and the development of an eddy zone on the lee side of the boulder. The extent of flow convergence and divergence is quantified by identifying the effective width, defined here as the width which conveys 90% of the highest modeled velocities. At low flow, the ratio of effective width between the pool and riffle is roughly 1:1, indicating little flow convergence or divergence. At bankfull discharge, the ratio of effective width is approximately 1:3 between the pool and downstream riffle, illustrating the strong flow convergence at the pool head. The effective width tends to equalize again with a ratio of 1:1 between the pool and riffle during a modeled discharge of a five-year flood, as the large roughness elements above the pool become drowned out. Results suggest that forced pool–riffle sequences in boulder-bed streams are maintained by flows at or near bankfull discharge because of stage-dependent variability in depth-averaged velocity and tractive force.     

Response of Plant Community Carbon and Nitrogen Stoichiometry to Experimental Warming on the Qinghai-Tibet Plateau

Low temperature is an important limiting factor for alpine ecosystems on the Tibetan Plateau. This study is based on data from on-site experimental warming platforms (open top chambers, OTC) at three elevations (4300 m, 4500 m, 4700 m) on the Qinghai-Tibet Plateau. The carbon and nitrogen stoichiometry characteristics of plant communities, both above-ground and below-ground, were observed in three alpine meadow ecosystems in August and September of 2011 and August of 2012. Experimental warming significantly increased above-ground nitrogen content by 21.4% in September 2011 at 4500 m, and reduced above-ground carbon content by 3.9% in August 2012 at 4300 m. Experimental warming significantly increased below-ground carbon content by 5.5% in August 2011 at 4500 m, and the below-ground ratio of carbon to nitrogen by 28.0% in September 2011 at 4300 m, but reduced below-ground nitrogen content by 15.7% in September 2011 at 4700 m, below-ground carbon content by 34.3% in August 2012 at 4700 m, and the below-ground ratio of carbon to nitrogen by 37.9% in August 2012 at 4700 m. Experimental warming had no significant effect on the characteristics of community carbon and nitrogen stoichiometry under other conditions. Therefore, experimental warming had inconsistent effects on the carbon and nitrogen stoichiometry of plant communities at different elevations and during different months. Soil ammonium nitrogen and nitrate nitrogen content were the main factors affecting plant community carbon and nitrogen stoichiometry.     

Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)

A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m⁻³) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m⁻³, with no prominent diatom bloom. Photosynthetic competence in terms of F _v/F _m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.     

中国贝类养殖对海洋碳循环的贡献评估

造成全球暖化的主要原因是温室气体的过量排放,其中CO2的贡献率达60 %,贝类养殖具有碳沉积作用。依据农业部渔业局编制的《中国渔业统计年签》,以2001年到2010年的年平均产量计算贝类捕获和养殖的碳沉积能力,并评估其碳沉积潜力;计算牡蛎、蛤、扇贝与贻贝四种贝壳单位面积的碳沉积能力并与森林、珊瑚礁的碳沉积能力进行比较分析。本文对我国浅海贝类养殖所具有的碳沉积能力进行评估,以了解贝类养殖对海洋碳循环的贡献,可为争取国家碳份额的合法权益提供基础数据。分析表明我国近十年贝类总产量稳定在1100万吨以上,并有增加的趋势,其中海水养殖贝类约占87.34 %。贝类养殖和捕获总产量的碳沉积和海水养殖产量的碳沉积量分别为58.57、51.15万吨/年,碳沉积能力分别相当于122.28、106.78万公顷的造林,可分别减少大气CO2增加量的0.0125 %、0.0109 %。牡蛎、蛤、扇贝与贻贝的单位面积碳沉积速率分别为1.573、0.388、0.301、1.039吨碳/(公顷?年);牡蛎和贻贝高于森林的碳沉积能力0.479吨碳/(公顷?年);但低于珊瑚礁的碳沉积能力1.8吨碳/(公顷?年)。我国贝类淡、海水养殖产量可分别创造约268.4万元/年、12,711.2万元/年的碳权商机。