Future impacts of drivers of change on wetland ecosystem services in Colombia

Wetlands are among the most valuable ecosystems in the world due to their delivery of ecosystem services (ES), but they are particularly vulnerable to drivers of land-use change. However, little is known about how different wetlands respond to drivers of land-use change and how that impacts their delivery of ES. After extreme floods hit Colombia in 2010–2011, negative impacts from these storms heightened the interest of Colombian policy-makers in understanding and recognizing the importance of wetlands. Here, we present a map with 19 wetland types for Colombia and assess the ES that these wetlands deliver and how those ES are impacted by drivers of land-use change. We based our spatial analysis on the Corine Land Cover data for Colombia and combined that with spatial indices derived from knowledgeable experts using the matrix approach and participatory mapping (PGIS). The most vulnerable wetland types identified were floodplain forests, riparian wetlands, freshwater lakes and rivers. The region of Magdalena-Cauca has been identified as the most vulnerable to the impacts of land-use change, until 2025. We discuss our results in light of the current Colombian policy-debate which concerns the designation of wetlands as strategic ecosystems. This designation implies necessary restrictions or prohibition of harmful activities in wetlands, principally mining and industrial agriculture.     

Population pressure and global markets drive a decade of forest cover change in Africa's Albertine Rift

Africa's Albertine Rift region faces a juxtaposition of rapid human population growth and protected areas, making it one of the world's most vulnerable biodiversity hotspots. Using satellite-derived estimates of forest cover change, we examined national socioeconomic, demographic, agricultural production, and local demographic and geographic variables, to assess multilevel forces driving local forest cover loss and gain outside protected areas during the first decade of this century. Because the processes that drive forest cover loss and gain are expected to be different, and both are of interest, we constructed models of significant change in each direction. Although rates of forest cover change varied by country, national population change was the strongest driver of forest loss for all countries – with a population doubling predicted to cause 2.06% annual cover loss, while doubling tea production predicted to cause 1.90%. The rate of forest cover gain was associated positively with increased production of the local staple crop cassava, but negatively with local population density and meat production, suggesting production drivers at multiple levels affect reforestation. We found a small but significant decrease in loss rate as distance from protected areas increased, supporting studies suggesting higher rates of landscape change near protected areas. While local population density mitigated the rate of forest cover gain, loss was also correlated with lower local population density, an apparent paradox, but consistent with findings that larger scale forces outweigh local drivers of deforestation. This implicates demographic and market forces at national and international scales as critical drivers of change, calling into question the necessary scales of forest protection policy in this biodiversity hotspot. Using a satellite derived estimate of forest cover change for both loss and gain added a dynamic component to more traditionally static and unidirectional studies, significantly improving our understanding of landscape processes and drivers at work.     

基于微博数据的北京市热点区域意象感知

“城市意象”研究对城市文化感知、城市管理与规划、旅游资源开发等具有重要意义。近年来,随着智能移动终端和社交媒体的普及,产生了大量城市内包含有文本和地理位置等信息的社交媒体数据,涉及城市的各个区域,为开展城市意象的综合感知研究提供了新的途径。本文以2016年北京市带位置签到的新浪微博数据为例,在空间聚类发现热点区域的基础上,采用词频—逆文件频率(TF-IDF)与文档主题生成模型LDA两类典型的文本分析的方法,挖掘城市不同热点区域的主题,以感知北京市不同热点区域的社会文化功能和人群行为,并在此基础上通过对热点区域高频主题词进行共词聚类分析,深度挖掘北京市的总体意象。研究表明,运用文本挖掘及地理大数据分析的城市意象研究方法,能及时感知人群在城市不同场所的活动、态度、偏好,从而揭示城市的社会文化及功能特征,是对刻画城市物质形态的城市意象五要素模型的重要补充。此外,以北京市热点区域为例的实证研究结果对现实中的城市特色传承与空间品质塑造等有一定的启发意义。     

Global trench migration velocities and slab migration induced upper mantle volume fluxes: Constraints to find an Earth reference frame based on minimizing viscous dissipation

Since the advent of plate tectonics different global reference frames have been used to describe the motion of plates and trenches. The difference in plate motion and trench migration between different reference frames can be substantial (up to 4 cm/yr). This study presents an overview of trench migration velocities for all the mature and incipient subduction zones on Earth as calculated in eight different global reference frames. Calculations show that, irrespective of the reference frame: (1) trench retreat always dominates over trench advance, with 62–78% of the 244 trench segments retreating; (2) the mean and median trench velocity are always positive (retreating) and within the range 1.3–1.5 cm/yr and 0.9–1.3 cm/yr, respectively; (3) rapid trench retreat is only observed close to lateral slab edges (< 1500 km); and (4) trench retreat is always slow far from slab edges (> 2000 km). These calculations are predicted by geodynamic models with a varying slab width, in which plate motion, trench motion and mantle flow result from subduction of dense slabs, suggesting that trench motion is indeed primarily driven by slab buoyancy forces and that proximity to a lateral slab edge exerts a dominant control on the trench migration velocity. Despite these four general conclusions, significant differences in velocities between such reference frames remain. It is therefore important to determine which reference frame most likely describes the true absolute velocities to get an understanding of the forces driving plate tectonics and mantle convection. It is here proposed that, based on fluid dynamic considerations and predictions from geodynamic modelling, the best candidate is the one, which optimises the number of trench segments that retreat, minimizes the trench–perpendicular trench migration velocity (v_T) in the centre of wide (> 4000 km) subduction zones, maximizes the number of retreating trench segments located within 2000 km of the closest lateral slab edge, minimizes the average of the absolute of the trench–perpendicular trench migration velocity (|v_T|) for all subduction zones on Earth, and minimizes the global upper mantle toroidal volume flux (_To) that results from trench migration and associated lateral slab migration (i.e. slab rollback or slab roll-forward). Calculations show that these conditions are best met in one particular Indo-Atlantic hotspot reference frame, where 75% of the subduction zones retreat, v_T in the centre of wide subduction zones ranges between − 3.5 and 1.8 cm/yr, 83% of the trench segments located within 2000 km of the closest lateral slab edge retreat, the average of |v_T| is 2.1 cm/yr, and _To = 456 km³/yr (lower limit) and 539 km³/yr (upper limit). Inclusion of all the incipient subduction zones on Earth results in slightly greater fluxes of 465 km³/yr (lower limit) and 569 km³/yr (upper limit). It is also found that this reference frame is close to minimizing the total sub-lithospheric upper mantle volume flux (_K) associated with motion of continental keels located below the major cratons. It is stressed, however, that _K is an order of magnitude smaller than _To, and thus of subordinate importance. In conclusion, the Indo-Atlantic hotspot reference frame appears preferable for calculating plate velocities and plate boundary velocities.     

生计安全研究的可视化分析

以Web of science 核心库中1991~2016年间收录主题为“livelihood security”的文献为基础,应用CiteSpace软件,采取突现词分析、关键词共现分析、文献共被引分析等方法对生计安全研究进行可视化分析。研究发现,干旱、健康、妇女、艾滋病、粮食安全、难民等是生计安全研究的前沿领域;生计安全研究热点主要包括生计结果类、生态环境类、生计策略类和重点地区类;生计安全研究的知识基础主要包括粮食安全、海洋资源、气候变化适应性等研究领域;从研究内容来看,中国生计安全研究主要包括自然资源与粮食安全、自然灾害与生计安全、快速城镇化与生计安全、气候变化与生计安全等4个方面。     

基于DMSP-OLS与NPP-VIIRS整合数据的中国三大城市群城市空间扩展时空格局

通过拟合最优幂函数模型,将NPP-VIIRS影像模拟为DMSP-OLS影像,构建了京津冀、长江三角洲（简称长三角）和珠江三角洲（简称珠三角）三大城市群1992—2017年长时间序列夜间灯光影像集。参考城市建成区统计数据确定夜间灯光最佳阈值提取城市范围,有效剥离统计数据中包含的经济活力不足的城市空间,识别出不属于统计范围的低等级、高活力城镇区,创新了数据应用视角。研究表明：① 县级城镇和市级以上城市对三大城市群城市范围的贡献度不同。京津冀腹地广阔,县级城镇是区域经济活力的重要组成部分,整体上贡献度最大;1990s初期长三角部分县级城镇经济活力较强,大量撤县设市后县级城镇数量减少,逐渐在2005年后低于京津冀;珠三角受到社会经济发展条件和行政单元划分的影响,县级城镇对城市范围的贡献在3个城市群中始终最小。② 三大城市群城市扩展非均衡性特征存在差异。京津冀城市扩展为京、津主导下的“双核”模式,非均衡性显著,尚未形成完善的城市规模体系;长三角和珠三角城市集聚特征明显,均衡性更强。重心迁移的路径、方向和距离反映各城市群不同的扩展强度和作用模式。③ 城市空间扩展格局整体均呈现热点区不断扩大、冷点区不断缩小的特征。其中京津冀热点和冷点区相对稳定,热点区向心集聚作用较强;长三角和珠三角空间格局变化较大,区域核心城市带动作用较强。     

Seismic evidence for a mantle plume beneath the Cape Verde hotspot

P- and S-wave tomography of the upper mantle beneath the Cape Verde hotspot is determined using arrival-time data measured precisely from three-component seismograms of 106 distant earthquakes recorded by a local seismic network. Our results show a prominent low-velocity anomaly imaged as a continuous column <100 km wide from the uppermost mantle down to about 500 km beneath Cape Verde, especially below the Fogo active volcano, which erupted in 1995. The low-velocity anomaly may reflect a hot mantle plume feeding the Cape Verde hotspot.     

澜沧江流域生态系统水源涵养功能研究

生态系统的水源涵养功能一直以来都是生态学和水文学研究的热点和难点问题。本文基于新开发的InVEST模型对澜沧江流域的水源涵养功能进行了研究,得出以下结果：（1）澜沧江流域年均供水7.24E＋10 m3 y-1,其中干流贡献率为23.87%,而支流贡献率为76.13%,从上游至下游呈明显递增趋势。（2）草地生态系统和森林生态系统的水源涵养量贡献率共计达71.66%;对不同组成结构生态系统类型的水源涵养能力进行比较,阔叶林〉针阔混交林〉竹林〉针叶林〉灌木林〉草地。（3）澜沧江流域三分之二的水由占总面积40%的热点区域提供。研究为澜沧江流域水资源的有效管理提供一定依据。     

A Paleogene magmatic overprint on Cretaceous seamounts of the western Pacific

The West Pacific Seamount Province (WPSP) represents a series of short-lived Cretaceous hotspot tracks. However, no intraplate volcanoes in advance of petit-spot volcanism erupted near a trench have been identified after the formation of the WPSP on the western Pacific Plate. This study reports new ages for Paleogene volcanic edifices within the northern WPSP, specifically the Ogasawara Plateau and related ridges, and Minamitorishima Island. These Paleogene ages are the first reported for basaltic rocks on western Pacific seamounts, in an area that has previously only yielded Cretaceous ages. The newly found Paleogene volcanisms overprint the Early–middle Cretaceous volcanic edifices, because the seamount or paleo-island material-covered reefal limestone caps on these edifices are uniformly older than the Paleogene volcanism identified in this study. This study outlines several possible causative factors for the Paleogene volcanism overprinting onto existing Cretaceous seamounts, including volcanism related to lithospheric stress, or a younger hotspot track within the northern part of the WPSP that records magmatism from ~60 Ma.     

利用POLDER数据验证MODIS BRDF模型参数产品及Ross-Li模型

将MODIS BRDF模型参数产品(MCD43A1)模拟的近红外波段反射率与从POLDER-3/PARASOL BRDF全球数据集中筛选的9961个像元的BRDF观测数据进行对比,验证了MCD43A1所采用的RossThick-LiSparseR BRDF 模型(Ross-Li模型)拟合二向反射的能力。结果表明,Ross-Li模型总体上可以有效地模拟地物的二向反射,所有像元的近红外波段反射率模拟值与POLDER-3观测数据之间的R²达到0.943,RMSE为0.016,模拟反射率比POLDER-3数据总体偏低5.2%。但Ross-Li模型明显低估了热点反射率,热点模拟结果比POLDER-3数据平均偏低14%,模拟值的R2为0.824,RMSE为0.07。热点反射率模拟误差与地表覆盖类型有关,针叶林热点反射率模拟值偏低最严重,其次是阔叶林、草地与农田,灌木与裸地热点反射率模拟值偏低相对较小。通过修正Ross-Li模型中的体散射核,可以明显改善热点反射率的模拟效果(R²＝0.839,RMSE＝0.043)。Ross-Li模型对天底、暗点等特征方向反射率的模拟较为准确。Ross-Li模型的模拟精度随太阳天顶角和观测天顶角的增大而降低。对于农田与草地而言,Ross-Li模型的模拟精度随NDVI的增加而降低;但在森林与灌木覆盖条件下,当NDVI约为0.5时,Ross-Li模型的模拟效果最差。