基于最大转子储能的风电场风机变利用率的有功功率分配策略优化

风机采用最大功率追踪控制时无功率备用量,当系统供需发生变化时,易对系统稳定性造成较大影响。提出了一种风场变利用率的有功功率分配策略,在满足系统调度命令的同时,减少风能的损失,提高风能利用率。考虑到风场的尾流效应,所提方案通过改变每台风力机的利用率来控制风机的有功功率输出。其中,每台风力机的利用率根据其自身转速而自适应调整。当风机转速较高时,风力机的利用率则较高。当风机转速较低时,则降低风力机的利用率,这样风电场可存储更多的旋转动能,可在系统需要时释放回系统。通过在基于双馈风机的风电场中对所提变利用率策略进行研究,结果表明,在满足调度需求的同时,所提控制策略比传统的等利用率方案更加节能。

Variation of Water-Use Efficiency of Leymus chinensis and Cleistogenes squarrosa in Different Plant Communities in Xilin River Basin, Nei Mongol

Water is usually considered to be a key limiting factor for the growth and reproduction of steppe plants in the Xilin River Basin, Nei Mongol. Foliar delta C-13 values, an indicator of long-term intercellular carbon dioxide concentration and thus of water-use efficiency (WUE) in plants, were measured on Leymus chinensis (Trin.) Tzvel. and Cleistogenes squarrosa (Trin.) Keng. in six communities of different habitats in die Xilin River Basin. The foliar delta C-13 values of both species tended to increase with decreasing soil water content (SWC) and a significant negative correlation was found between foliar delta C-13 Values and SWC in different soil layers, indicating that the two species could change WUE according to water availability. We also found relatively constant leaf water contents (LWC) of the two species in different habitats. Our results implied that the two steppe species might have adapted to different soil water regimes either through adjusting stomatal conductance to get a proper WUE, or through enhancing the osmosis-regulating ability to keep a relatively stable LWC. Our findings could partially explain why the two plant species have a wide distribution range and become dominant in the Xilin River Basin.

Evaluating the impacts of land use and land cover changes on surface air temperature using the WRF-mosaic approach

Satellite-derived land surface data in 1980 and 2010 were used to represent land use and land cover（LULC） changes caused by the rapid economic development and human activities that have occurred over the past few decades in East Asia and China. The effects of LULC changes on the radiation budget and 2-m surface air temperature（SAT） were explored for the period using the Weather Research and Forecasting（WRF） model. The mosaic approach, which considers the N-most abundant land use types within a model grid cell（here, N = 3） and precisely describes the subgridscale LULC changes, was adopted in the integrations. The impacts of LULC changes based on two 36-year integrations showed that SAT generally decreased, with the sole exception being over eastern China, resulting in decreased SAT in China（-0.062 °C） and East Asian land areas（EAL,-0.061 °C）. The LULC changes induced changes in albedo, which influenced the radiation budget. The radiative forcings at the top of the atmosphere were-0.56 W m-2 across the whole of China, and-0.50 W m-2 over EAL. Meanwhile, the altered roughness length mainly influenced near-surface wind speeds, large-scale and upward moisture fluxes, latent heat fluxes, and cloud fractions at different altitudes. Though the impacts caused by the LULC changes were generally smaller at regional scales, the values at local scales were much stronger.

Positive adaptation of Salix eriostachya to warming in the treeline ecotone,East Tibetan Plateau

Understanding of treeline ecotone ecophysiological adaptation to climate warming is still very limited. Furthermore, it is difficult to predict which plant species could dominate in the future. For this reason, a study was conducted in the treeline ecotone, East Tibetan Plateau to detect the adaptation of the dwarf willow(Salix eriostachya) to experimental warming. Compared to ambient conditions, the experimental warming advanced the bud break by 12 days, delayed the leaf abscission by20 days, and prolonged the growing period by 28 days.It also increased photosynthesis(47%), number of leaves(333%), leaf area(310%), and carbon sequestration of the dwarf willow. Experimental warming did not affect carbon use efficiency, but decreased water use efficiency significantly.Experimental warming enhanced the clonal ramets of Salix eriostachya(+ 3.7 shrubs m-2). The frequent air temperature fluctuations had minor effect on Salix eriostachya. Based on these findings, we highlighted that Salix eriostachya could dominate in the community treeline ecotone of east Tibetan Plateau in the future climate warming scenario.

Spatial assessment of forest cover and land-use changes in the Hindu-Kush mountain ranges of northern Pakistan

Anthropogenic activities and natural processes are continuously altering the mountainous environment through deforestation, forest degradation and other land-use changes. It is highly important to assess, monitor and forecast forest cover and other land-use changes for the protection and conservation of mountainous environment. The present study deals with the assessment of forest cover and other land-use changes in the mountain ranges of Dir Kohistan in northern Pakistan, using high resolution multi-temporal SPOT-5 satellite images. The SPOT-5 satellite images of years 2004, 2007, 2010 and 2013 were acquired and classified into land-cover units. In addition, forest cover and land-use change detection map was developed using the classified maps of 2004 and 2013. The classified maps were verified through random field samples and Google Earth imagery(Quick birds and SPOT-5). The results showed that during the period 2004 to 2013 the area of forest land decreased by 6.4%, however, area of range land and agriculture land have increased by 22.1% and 2.9%, respectively. Similarly, barren land increased by 1.1%, whereas, area of snow cover/glacier is significantly decreased by 21.3%. The findings from the study will be useful for forestry and landscape planning and can be utilized by the local, provincial and national forest departments; and REDD+ policy makers in Pakistan.

Historical Sediment Record of ^(137)Cs, δ-HCH, and δ^(13)C Reflects the Impact of Land Use on Soil Erosion

This paper reports the concentrations of 137Cs, hexaehlorocyclohexane （HCH）, dichlorodiphenyltrichloroethanes （DDT） and its main degradation products, δ3C, and organic carbon in pond sediments （O-210 cm, sectioned by 2-20 cm interval） and surface soils （the 0-3 cm horizon） collected in 2OlO from Chenjia catchment, which is located in Yanting county in the hilly central Sichuan of China. α-, β-, and γ-HCH, DDT, and DDD were not detected throughout the sediment profile. Trace concentrations of δ-HCH （0.89-29.31 ng g^-1） and p,p＇- DDE （1.85-6.02 ng g^-1） were detected only in top 40 cm sediment. The 137Cs fallout peak in 1963 （corresponding to the 55-60 cm depth）, the sedimentary signature left by the last year of HCH use in 1989 （an additional indicator at 20-25 cm）, and the obvious original channel bed prior to the construction of the pond in 1956 were used as temporal markers to estimate changes in average sedimentation rate between different periods due to changes in land use. Continuous, marked decrease in average sedimentation rate （i.e., 3.79, 1.35 and 1.07 cm year-1 in 1956-1963, 1963-1989, and 1989-2010, respectively） over time was observed, probably due to the reforestation, abandoning of steep sloping farmland for afforestation and natural re-vegetation （implementation of the Grain for Green Program）, and the conversion of part of gently sloping farmlandterraces to orchard land since the 1980s, especially since the 1990s. This was corroborated by the observed decrease （more negative） in δ3C of sediment towards the surface, which indicates increased relative contribution of eroded soil particles coming from slopes with increased tree cover in sediment source area. Combined use of 137Cs, δ-HCH, and δ3C record in sediments has been demonstrated to be a powerful approach to reconstruction of response in sedimentation rate to historical land use changes.

Principal Denudation Processes and Their Contribution to Fluvial Suspended Sediment Yields in the Upper Yangtze River Basin and Volga River Basin

This paper synthesized the principal land denudation processes and their role in determining riverine suspended sediment yields(SSY) in two typical geographical environments of the Upper Yangtze River Basin in China and the Volga River Basin in Eastern Europe. In the Upper Yangtze River Basin, natural factors including topography, climate,lithology and tectonic activity are responsible for the spatial variation in the magnitude of denudation rates.Human disturbances have contributed to the temporal changes of soil erosion and fluvial SSY during the past decades. On one hand, land use change caused by deforestation and land reclamation has played an important role in the acceleration of sediment production from the central hilly area and lower Jinsha catchment; On the other hand, diverse soil conservation practices(e.g., reforestation,terracing) have contributed to a reduction of soil erosion and sediment production since the late 1980 s.It was difficult to explicitly decouple the effect of mitigation measures in the Lower Jinsha River Basindue to the complexity associated with sediment redistribution within river channels(active channel migration and significant sedimentation). The whole basin can be subdivided into seven sub-regions according to the different proportional inputs of principal denudation processes to riverine SSY. In the Volga River Basin, anthropogenic sheet, rill and gully erosion are the predominant denudation processes in the southern region, while channel bank and bed erosion constitutes the main source of riverine suspended sediment flux in the northern part of the basin. Distribution of cultivated lands significantly determined the intensity of denudation processes.Local relief characteristics also considerably influence soil erosion rates and SSY in the southern Volga River Basin. Lithology, soil cover and climate conditions determined the spatial distribution of sheet, rill and gully erosion intensity, but they play a secondary role in SSY spatial variation.

Effect of Biochar Addition on Maize Growth and Nitrogen Use Efficiency in Acidic Red Soils

Biochar added to soil can improve crop growth through both direct and indirect effects, particularly in acidic, highly weathered soils in subtropical and tropical regions. However, the mechanisms of biochar improving crop growth are not well understood. The objectives of this study were i) to determine the crop responses to biochar addition and ii) to understand the effect of biochar addition on N use efficiency. Seven acidic red soils varying in texture, p H, and soil nutrient were taken from southern China and subjected to four treatments: zero biochar and fertilizer as a control(CK), 10 g kg-1biochar(BC), NPK fertilizers(NPK), and 10 g kg-1biochar plus NPK fertilizers(BC+NPK).15N-labeled fertilizer was used as a tracer to assess N use efficiency. After a 46-d pot experiment,biochar addition increased soil p H and available P, and decreased soil exchangable Al3+, but did not impact soil availabe N and cation exchange capacity(P > 0.05). The N use efficiency and N retained in the soil were not significantly affected by biochar application except for the soil with the lowest available P(3.81 mg kg-1) and highest exchanageable Al3+(4.54 cmol kg-1). Greater maize biomass was observed in all soils amended with biochar compared to soils without biochar(BC vs. CK, BC+NPK vs. NPK). This agronomic effect was negatively related to the concentration of soil exchangeable Al3+(P < 0.1). The results of this study implied that the liming effect of biochar improved plant growth through alleviating Al toxicity and P deficiency, especially in poor acidic red soils.

Projections of land use changes under the plant functional type classification in different SSP-RCP scenarios in China

Land use projections are crucial for climate models to forecast the impacts of land use changes on the Earth’s system.However,the spatial resolution of existing global land use projections(e.g.,0.25°×0.25°in the Land-Use Harmonization(LUH2)datasets)is still too coarse to drive regional climate models and assess mitigation effectiveness at regional and local scales.To generate a high-resolution land use product with the newest integrated scenarios of the shared socioeconomic pathways and the representative concentration pathways(SSPs-RCPs)for various regional climate studies in China,here we first conduct land use simulations with a newly developed Future Land Uses Simulation(FLUS)model based on the trajectories of land use demands extracted from the LUH2 datasets.On this basis,a new set of land use projections under the plant functional type(PFT)classification,with a temporal resolution of 5 years and a spatial resolution of 5 km,in eight SSP-RCP scenarios from 2015 to 2100 in China is produced.The results show that differences in land use dynamics under different SSP-RCP scenarios are jointly affected by global assumptions and national policies.Furthermore,with improved spatial resolution,the data produced in this study can sufficiently describe the details of land use distribution and better capture the spatial heterogeneity of different land use types at the regional scale.We highlight that these new land use projections at the PFT level have a strong potential for reducing uncertainty in the simulation of regional climate models with finer spatial resolutions.

Highly dispersed L1_(0)-PtZn intermetallic catalyst for efficient oxygen reduction

Highly active and durable electrocatalysts with minimal Pt usage are desired for commercial fuel cell applications.Herein,we present a highly dispersed L1_(0)-PtZn intermetallic catalyst for the oxygen reduction reaction(ORR),in which a Zn-rich metal–organic framework(MOF)is used as an in situ generated support to confine the growth of PtZn particles.Despite requiring high-temperature treatment,the intermetallic L1_(0)-PtZn particles exhibit a small mean size of3.95 nm,which confers the catalysts with high electrochemical active surface area(81.9 m^(2)g_(Pt)^(-1))and atomic utilization.The Pt electron structure and binding strength between Pt and oxygen intermediates are optimized through ligand effect and compressive strain.These advantages result in ORR mass activity and specific activity of 0.926 A mg_(Pt)^(-1) and 1.13 mA cm^(-2),respectively,which are 5.4 and 4.0 times those of commercial Pt/C.The stable L10structure provides the catalysts with superb durability;only a halfwave potential loss of 11 mV is observed after 30,000 cycles of accelerated stress tests,through which the structure evolves into a more stable PtZn-Pt core-shell structure.Therefore,the development of a Zn-based MOF as a catalyst support is demonstrated,providing a synergy strategy to prepare highly dispersed intermetallic alloys with high activity and durability.

The effects of an experimental drought on the ecophysiology and fruiting phenology of a tropical rainforest palm

Aims Anthropogenic climate change is predicted to increase mean temperatures and rainfall seasonality.How tropical rainforest species will respond to this climate change remains uncertain.Here,we analysed the effects of a 4-year experimental throughfall exclusion(TFE)on an Australian endemic palm(Normambya normanbyi)in the Daintree rainforest of North Queensland,Australia.We aimed to understand the impact of a simulated reduction in rainfall on the species’physiological processes and fruiting phenology.Methods We examined the fruiting phenology and ecophysiology of this locally abundant palm to determine the ecological responses of the species to drought.Soil water availability was reduced overall by~30%under a TFE experiment,established in May 2015.We monitored monthly fruiting activity for 8 years in total(2009–2018),including 4 years prior to the onset of the TFE.In the most recent year of the study,we measured physiological parameters including photosynthetic rate,stomatal conductance and carbon stable isotopes(δ13C,an integrated measure of water use efficiency)from young and mature leaves in both the dry and wet seasons.Important Findings We determined that the monthly fruiting activity of all palms was primarily driven by photoperiod,mean solar radiation and mean temperature.However,individuals exposed to lower soil moisture in the TFE decreased significantly in fruiting activity,photosynthetic rate and stomatal conductance.We found that these measures of physiological performance were affected by the TFE,season and the interaction of the two.Recovery of fruiting activity in the TFE palms was observed in 2018,when there was an increase in shallow soil moisture compared with previous years in the treatment.Our findings suggest that palms,such as the N.normanbyi,will be sensitive to future climate change with long-term monitoring recommended to determine population-scale impacts.