ALBERT

Description: Changes in spring vegetation phenology and production will presumably impact the velocity of greenup (Vgreenup, daily rate of changes in productivity during greenup period), yet little is currently known about the spatiotemporal patterns of global Vgreenup. Here, we define Vgreenup as the ratio of the amplitude of greenup to the duration of greenup, and derive global Vgreenup from 34‐year satellite leaf area index observations to study its spatiotemporal dynamics. The results suggest that combined effects of climate change and human land management have greatly accelerated global Vgreenup, with important implications for changes in terrestrial ecosystem functioning and global carbon cycling. Abstract Global warming and human land management have greatly influenced vegetation growth through both changes in spring phenology and photosynthetic primary production. This will presumably impact the velocity of vegetation greenup (Vgreenup, the daily rate of changes in vegetation productivity during greenup period), yet little is currently known about the spatio‐temporal patterns of Vgreenup of global vegetation. Here, we define Vgreenup as the ratio of the amplitude of greenup (Agreenup) to the duration of greenup (Dgreenup) and derive global Vgreenup from 34‐year satellite leaf area index (LAI) observations to study spatio‐temporal dynamics of Vgreenup at the global, hemispheric, and ecosystem scales. We find that 19.9% of the pixels analyzed (n = 1,175,453) experienced significant trends toward higher greenup rates by an average of 0.018 m2 m−2 day−1 for 1982–2015 as compared to 8.6% of pixels with significant negative trends (p 〈 0.05). Global distribution and dynamics of Vgreenup show high spatial heterogeneity and ecosystem‐specific patterns, which is primarily determined by the high spatial variation in Agreenup, while the temporal dynamics of Vgreenup are directly controlled by both changes in Dgreenup and Agreenup. Areas with the largest Vgreenup and largest positive trends are both observed in deciduous and mixed forests as compared to nonforest ecosystems showing both lower Vgreenup and trends. For nonforest ecosystems, human‐managed ecosystems (e.g., rangelands and rainfed croplands) exhibited higher Vgreenup and positive trends than those of natural counterparts, suggesting strong imprints of human land management on terrestrial ecosystem functioning. Globally, warming has accelerated Vgreenup in temperature‐constrained high latitude forest ecosystems and arctic regions, but decelerated Vgreenup in temperate and arid/semiarid areas. These results suggest that the combined effects of climate change and human land management have greatly accelerated global vegetation greenup, with important implications for changes in terrestrial ecosystem functioning and global carbon cycling.

Description: Two diel field campaigns under different weather patterns were carried out in the summer and autumn of 2013 to measure CO 2 and CH 4 fluxes and to probe the rates of gas exchange across the air–water interface in a subtropical eutrophic pond in China. Bubble emissions of CH 4 accounted for 99.7 and 91.67% of the total CH 4 emission measured at two sites in the summer; however, no bubble was observed in the autumn. The pond was supersaturated with CO 2 and CH 4 during the monitoring period, and the saturation ratios (i.e. observed concentration/equilibrium concentration) of CH 4 were much higher than that of CO 2 . Although the concentration of dissolved CO 2 in the surface water collected in the autumn was 1.24 times of that in the summer, the mean diffusive CO 2 flux across the water–air interface measured in the summer is almost twice compared with that in the autumn. The mean concentration of dissolved CH 4 in the surface water in the autumn was around half of that in the summer, but the mean diffusive CH 4 flux in the summer is 4–5 times of that in the autumn. Our data showed that the variation in gas exchange rate was dominated by differences in weather patterns and primary production. Averaged k 600 -CO 2 and k 600 -CH 4 (the gas transfer velocity normalised to a Schmidt number of 600) were 0.65 and 0.55 cm/h in the autumn, and 2.83 and 1.64 cm/h in the summer, respectively. No statistically significant correlation was found between k 600 and U 10 (wind speed at 10 m height) in the summer at low wind speeds in clear weather. Diffusive gas fluxes increased during the nights, which resulted from the nighttime cooling effect of water surface and stronger turbulent mixing in the water column. The chemical enhancements for CO 2 were estimated up to 1.94-fold in the hot and clear summer with low wind speeds, which might have been resulted from the increasing hydration reactions in water due to the high water temperature and active metabolism in planktonic algae. However, both the air and surface water temperatures decreased continually, and relatively lower temperature and overcast weather with occasionally light rain dominated the second campaign in the autumn. The concentration of dissolved oxygen in the surface water and U 10 controlled gas transfer velocities of CO 2 and CH 4 , respectively, in the cool autumn. When the surface water temperature was higher than the air temperature, higher CO 2 flux was observed because the water body was unstable and overturned quickly, inducing quick CO 2 emitted from plankton algae in surface water to the atmosphere. Keywords: gas transfer velocity, the chemical enhancement, convective cooling, wind speed, pond, subtropical, primary productivity (Published: 9 December 2014) Citation: Tellus B 2014, 66 , 23795, http://dx.doi.org/10.3402/tellusb.v66.23795

Description: Mapping land surface water bodies from satellite images is superior to conventional in situ measurements. With the mission of long-term and high-frequency water quality monitoring, the launch of the Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3A and Sentinel-3B provides the best possible approach for near real-time land surface water body mapping. Sentinel-3 OLCI contains 21 bands ranging from visible to near-infrared, but the spatial resolution is limited to 300 m, which may include lots of mixed pixels around the boundaries. Sub-pixel mapping (SPM) provides a good solution for the mixed pixel problem in water body mapping. In this paper, an unsupervised sub-pixel water body mapping (USWBM) method was proposed particularly for the Sentinel-3 OLCI image, and it aims to produce a finer spatial resolution (e.g., 30 m) water body map from the multispectral image. Instead of using the fraction maps of water/non-water or multispectral images combined with endmembers of water/non-water classes as input, USWBM directly uses the spectral water index images of the Normalized Difference Water Index (NDWI) extracted from the Sentinel-3 OLCI image as input and produces a water body map at the target finer spatial resolution. Without the collection of endmembers, USWBM accomplished the unsupervised process by developing a multi-scale spatial dependence based on an unsupervised sub-pixel Fuzzy C-means (FCM) clustering algorithm. In both validations in the Tibet Plate lake and Poyang lake, USWBM produced more accurate water body maps than the other pixel and sub-pixel based water body mapping methods. The proposed USWBM, therefore, has great potential to support near real-time sub-pixel water body mapping with the Sentinel-3 OLCI image.

Description: To realize the maximum accommodation of renewable energy of two regions, the paper has studied many influencing factors including renewable energy theoretical output curve, load characteristics, operation constraints of units and operation characteristics of UHV line. The weekly renewable energy inter-regional accommodation model is proposed based on time sequential simulation, considering the reserve of system, maintenance of units, trading power of two regions, power plan of conventional units and so on. An inter-regional system consisting of two IEEE 30 bus systems is used as an example. The sensitivity of influencing factors is analysed to prove the effectiveness and rationality of the proposed model. The research results could be available for dispatching agency to formulate the dispatching plan.

Description: This paper studied in detail the chemical effects of CO 2 on methane laminar flame speed in O 2 /CO 2 atmosphere both experimentally and numerically. Experimentally, flames were established in the counterflow configuration at atmosphere pressure with inlet temperature (Tu) of 293K and the methane laminar flame speed ( ##IMG## [http://ej.iop.org/images/1755-1315/186/2/012050/EES_186_2_012050_ieqn1.gif] {${{\rm{S}}}_{{\rm{u}}}^{0}$} ) in O 2 /CO 2 atmosphere was measured with the help of PIV technique. Numerically, A comprehensive comparison between the flame speeds in O 2 /CO 2 atmosphere and O 2 /N 2 atmosphere with an identical mole fraction of O 2 is established by introducing the artificial materials U, V, W, X, Y, Z to gradually isolate the effects of chemical properties and specific heat, mass diffusivity, radiation, thermal conductivity and density. A detaile...

Description: The problem of heavy metal pollution in soil restricts the sustainable development of agricultural production in China, especially the cadmium-contaminated vegetable fields seriously endanger food safety. How to control and repair cadmium pollution in vegetable land is an urgent problem to be solved. The status and sources of cadmium pollution in vegetable fields in China were reviewed, and the phytoremediation pathways of cadmium pollution in vegetable fields were elaborated, in order to provide references for remediation of cadmium pollution in vegetable fields.

Description: Magnetically driven superhydrophobic materials were coated on the surface of polyurethane sponges by Fe 3 O 4 nanoparticals and stearic acid. The as-prepared sponge was characterized by scanning electron microscope, fourier transform infrared spectroscopy and other analytical techniques. The surface wettability of the as-prepared sponge, the separation capacity of oil/water mixtures and emulsions, the sorption kinetics of different types of oil, and the recyclability of the materials were studied. The Fe 3 O 4 and stearic acid were coated onto the skeleton surface of the sponge, which make the as-prepared sponge possess magnetic and hierarchically microstructure. The water contact angle reach up to 158° on the surface of the superhydrophobic sponge. The materials also shows highly efficient oil/water mixtures and emulsions separation. Moreover, the oil separation capacities still keep a high value after 50 cycles of squeezing the saturated a...