全球贸易自由化对中国和世界经济的影响

全球贸易自由化是当前和未来世界经济发展不可避免的趋势,2001年开始的多哈回合贸易自由化多边谈判和最近刚刚取消的“多种纤维协定”（MFA）将在全球贸易自由化进程中发挥重要的作用。本研究的目的是通过一些案例分析,揭示贸易自由化对中国和世界经济的影响。采用全球贸易模型,我们分析了MFA和在多哈回合初期欧盟、美国和凯恩斯集团分别提出的贸易自由化提案。研究结果表明,虽然取消MFA对一些国家纺织部门带来冲击,但它极大地促进了大多数国家经济的发展,改善了全球福利;多哈谈判过程中提出的各种贸易自由化提案都在不同程度上促进世界经济的发展,但其影响大小依次为凯恩斯提案、美国提案和欧盟提案;贸易自由化对经济的影响在不同部门和不同国家间存在显著差别;更大程度的贸易自由化不但符合全球共同利益,也符合中国国家利益;中国在推动全球贸易自由化过程中应发挥更积极和更大的作用。     

临界转换的早期预警信号

从生态系统到金融市场和气候在内的很多复杂动力系统,都会有临界点,在这样的点上系统可能会发生突变,从而演变到一个对立的动力模式上。在这样的临界点到达之前对其进行预测极为困难,但是现在,不同科学领域的研究工作表明,普遍性的早期预警信号有迹可循。对一系列不同类型的系统来说,这些信号会指示是否正在趋近一个临界阈值。     

The lateglacial Quercus expansion in the southern European Alps: rapid vegetation response to a late Allerød climate warming?

A pollen‐inferred vegetation shift, from pioneer birch–pine woodland to mixed pine–summergreen oak forests, in the southern Alpine forelands, is commonly attributed to a centennial‐scale warming that occurred between the Gerzensee Oscillation (GO) and the Younger Dryas. Two microtephra layers bracketing the Younger Dryas onset (the Laacher See Tephra and the Vedde Ash) improve the chronology at Lago Piccolo di Avigliana (northern Italy) and allowed accurate correlation with Central European records where the GO is clearly detected. We used pollen percentages, pollen accumulation rates (PARs) and plant macrofossils to assess the population dynamics of Quercus, and leaf‐cuticle analysis for a better taxonomic identification of Quercus. Our results indicate that the species that was locally present was probably Quercus robur. PARs suggest that the population expansion started as early as the Bølling and followed an exponential increase through time. We attribute this gradual shift to increasing summer temperatures and longer growing seasons which contrast with a gradually decreasing temperature trend as recorded in Greenland ice cores and in Central Europe. Breaks or set‐backs in the PAR record may indicate the biotic response to minor Lateglacial cooling events of different life‐history stages in the Quercus population. Copyright © 2011 John Wiley & Sons, Ltd.     

Ressi experimental catchment: Ecohydrological research in the Italian pre-Alps

Ressi is a small (2.4 ha) forested catchment located in the Italian pre-Alps. The site became an experimental catchment to investigate the water fluxes in the soil–plant–atmosphere continuum and the impact of vegetation on runoff generation in 2012. The elevation of the catchment ranges from 598 to 721 m a.s.l. and the climate is humid temperate. The bedrock consists of rhyolites and dacites; the soil is a Cambisol. The catchment is covered by a dense forest, dominated by beech, chestnut, maple, and hazel trees. The field set up includes measurements of the rainfall in an open area, streamflow at the outlet, soil moisture at various depths and locations, and depth to water table in six piezometers at a 5- or 10-min interval. Samples of precipitation, stream water, shallow groundwater and soil water are collected monthly for tracer analysis (stable isotopes (²H and ¹⁸O), electrical conductivity and major ions), and during selected rainfall–runoff events to determine the contribution of the various sources to runoff. Since 2017, soil and plant water samples have been collected to determine the sources of tree transpiration. Data collected in the period 2012–2016 are publicly available. Data collection is ongoing, and the data set is expected to be updated on an annual basis to include the most recent measurements.     

Zircon fission‐track ages from Newfoundland—A proxy for high geothermal gradients and exhumation before opening of the Central Atlantic Ocean

Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.     

Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya

Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 10⁶ m³ year^?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.     

A hydropedological approach to simulate streamflow and soil water contents with SWAT+

Reflecting internal catchment hydrological processes in hydrological models is important for accurate predictions of the impact of climate and land-use change on water resources. Characterizing these processes is however difficult and expensive due to their dynamic nature and spatio-temporal variability. Hydropedology is a relatively new discipline focusing on the synergistic integration of hydrology, soil physics and pedology. Hydropedological interpretations of soils and soil distribution can be used to characterize key hydrological processes, especially in areas with no or limited hydrometric measurements. Here we applied a hydropedological approach to reflect flowpaths through detailed routing in SWAT+ for a 157 ha catchment (Weatherley) in South Africa. We compared the hydropedological approach and a standard (no routing) approach against measured streamflow (two weirs) and soil water contents (13 locations). The catchment was treated as ‘ungauged’ and the model was not calibrated against hydrometric measurements in order to determine the direct contribution of hydropedology on modelling efficiency. Streamflow was predicted well without calibration (NSE > 0.8; R² > 0.82) for both approaches at both weirs. The standard approach yielded slightly better streamflow predictions. The hydropedological approach resulted in considerable improvements in the simulation of soil water contents (R² increased from 0.40 to 0.49 and PBIAS decreased from 40% to 20%). The routing capacity of SWAT+ as employed in the hydropedological approach reduced the underestimation of wetland water regimes drastically and resulted in a more accurate representation of the dominant hydrological processes in this catchment. We concluded that hydropedology can be a valuable source of ‘soft data’ to reflect internal catchment structure and processes and, potentially, for realistic calibrations in other studies, especially those conducted in areas with limited hydrometric measurements.     

Spatiotemporal variability in hydrochemistry of shallow groundwater in a small pre‐alpine catchment: The importance of landscape elements

Topography and landscape characteristics affect the storage and release of water and, thus, groundwater dynamics and chemistry. Quantification of catchment scale variability in groundwater chemistry and groundwater dynamics may therefore help to delineate different groundwater types and improve our understanding of which parts of the catchment contribute to streamflow. We sampled shallow groundwater from 34 to 47 wells and streamflow at seven locations in a 20‐ha steep mountainous catchment in the Swiss pre‐Alps, during nine baseflow snapshot campaigns. The spatial variability in electrical conductivity, stable water isotopic composition, and major and trace ion concentrations was large and for almost all parameters larger than the temporal variability. Concentrations of copper, zinc, and lead were highest at sites that were relatively dry, whereas concentrations of manganese and iron were highest at sites that had persistent shallow groundwater levels. The major cation and anion concentrations were only weakly correlated to individual topographic or hydrodynamic characteristics. However, we could distinguish four shallow groundwater types based on differences from the catchment average concentrations: riparian zone‐like groundwater, hillslopes and areas with small upslope contributing areas, deeper groundwater, and sites characterized by high magnesium and sulfate concentrations that likely reflect different bedrock material. Baseflow was not an equal mixture of the different groundwater types. For the majority of the campaigns, baseflow chemistry most strongly resembled riparian‐like groundwater for all but one subcatchment. However, the similarity to the hillslope‐type groundwater was larger shortly after snowmelt, reflecting differences in hydrologic connectivity. We expect that similar groundwater types can be found in other catchments with steep hillslopes and wet areas with shallow groundwater levels and recommend sampling of groundwater from all landscape elements to understand groundwater chemistry and groundwater contributions to streamflow.     

Preservation of Re‐Os isotope signatures in pyrite throughout low‐T,high‐P eclogite facies metamorphism

Pyrite in LT–HP eclogites from the western Tianshan orogenic belt yields a Re‐Os age of 378.1 ± 8.9 Ma, which is 30–70 Ma older than ages previously obtained for the same rocks using the Rb–Sr, Sm–Nd, Ar–Ar, U–Pb, and Lu–Hf isotope systems. The Tianshan LT–HP eclogite experienced temperatures of up to ~570 °C combined with pressures of up to 2.1 GPa during metamorphism. These conditions are below the transition of pyrite to pyrrhotite, which defines both pyrite stability and possibly its closure temperature for Re‐Os. Pyrite can preserve Re‐Os signatures through eclogite facies peak metamorphic conditions, and thus allow determination of the formation age of pyrite in the protolith.