Effects of the natural restoration time of abandoned farmland in a semiarid region on the soil denitrification rates and abundance and community structure of denitrifying bacteria.

Denitrification accounts for the production of mobile forms of nitrogen (N) for plant uptake, N leaching, and gaseous losses. However, few studies have investigated the potential effects of the natural restoration age on denitrification rates and denitrifying microorganisms, especially in fragile ecosystems in semiarid regions. The potential N gas (N2O and N2) emissions and denitrification rates significantly decreased after abandonment (< 9 years) compared to those of active farmland and then steadily increased as the restoration proceeded, leading to an enhanced soil N loss. The total bacterial and napA gene abundances significantly decreased after abandonment (< 9 years) compared to that of farmland and then significantly increased as the restoration proceeded. The abundances of the narG, nirK, nirS, qnorB, and nosZ genes steadily increased with the restoration age of abandoned farmland. The community compositions of denitrifying bacteria exhibited different fluctuating patterns, suggesting different response patterns of community traits of N gas emission-related functional guilds to the restoration age of abandoned farmland. Changes in N gas emissions and in the abundance and diversity of denitrifying microorganisms exhibited similar patterns, suggesting an increased population and diversity of denitrifying bacteria are responsible for the enhanced N gas emissions. We observed clear patterns of plant coverage and denitrifying microorganisms that were associated with increases in the organic C, NH4+-N, and NO3--N contents and decreases in the soil bulk density as well as increases in the abundance and diversity of denitrifiers with the restoration age of abandoned farmland that were linked to an increase in N gas emissions. It is therefore recommended that effective measures (i.e., modest levels of grazing) may be able to be undertaken to assist with decreasing greenhouse gas nitrous oxide (N2O) and N loss after 32 years of farmland abandonment.

Differential expression of CuZnSOD gene under low temperature stress in noble scallop Chlamys nobilis with different carotenoid content.

The noble scallop Chlamys nobilis belongs to a warm-water mollusk and has been cultured in the sea of southern China since 1980s'. However, accidents of massive mortality have often occurred during the winter, and one of the reasons could be accumulation of harmful reactive oxygen species caused by lower temperature. Carotenoids are well known for their anti-oxidant function. To investigate whether carotenoids do play a role in mollusks' antioxidant defense system under lower temperature stress, an acute lower temperature experiment was conducted by using two types of scallops: the orange with higher carotenoids content and the brown with lower carotenoids content. Their CuZnSOD gene was cloned, mRNA expression levels were determined, and SOD activity and carotenoids content were measured. The complete CuZnSOD cDNA consists of 1078 nucleotides with an open reading frame encoding 154 amino acid residues, which has high identity with that of its sister species Chlamys farreri. The mRNA expression levels in both the mantle and gill from the orange scallops were significantly higher (P < 0.05) than that of the brown ones, but the result was the opposite in the blood. SOD activity in the mantle and gill from the orange scallops was significantly higher than (P < 0.05) that from the brown ones. Further, significantly positive correlations were found among CuZnSOD gene transcript levels, SOD activity and total carotenoids content in the orange scallops. The present results suggested that carotenoids could play roles in antioxidant defense system by upregulating gene expression under lower temperature stress in the noble scallop.

Complex-Amplitude Programmable Versatile Metasurface Platform Driven by Guided Wave.

Metasurfaces have shown unparalleled controllability of electromagnetic (EM) waves. However, most of the metasurfaces need external spatial feeding sources, which renders practical implementation quite challenging. Here, a low-profile programmable metasurface with 0.05λ0 thickness driven by guided waves is proposed to achieve dynamic control of both amplitude and phase simultaneously. The metasurface is fed by a guided wave traveling in a substrate-integrated waveguide, avoiding external spatial sources and complex power divider networks. By manipulating the state of the p-i-n diodes embedded in each meta-atom, the proposed metasurface enables 1-bit amplitude switching between radiating and nonradiating states, as well as a 1-bit phase switching between 0° and 180°. As a proof of concept, two advanced functionalities, namely, low sidelobe-level beam scanning and Airy beam generation, are experimentally demonstrated with a single platform operating in the far- and near-field respectively. Such complex-amplitude, programmable, and low-profile metasurfaces can overcome integration limitations of traditional metasurfaces, and open up new avenues for more accurate and advanced EM wave control within an unprecedented degree of freedom.

Occurrence and distribution of microplastics in surface sediments of a typical river with a highly eroded catchment, a case of the Yan River, a tributary of the Yellow River.

Investigation of microplastic contamination in riverbed sediments can help clarify long-term microplastic pollution and establish prevention measures in watersheds. However, little research has been conducted on riverbed sediment pollution on the Loess Plateau, a highly eroded area in Northwest China. This research investigates the Yan River as a case study. The occurrence and distribution of microplastics were surveyed and analyzed to explore the microplastic pollution in the riverbed of the Loess Plateau. Microplastics were found in all sediment samples, with an abundance of 208.89-686.67 items kg-1. Polypropylene and polyethylene were the main microplastic components identified using Fourier transform infrared spectrometry and imaging systems. Particles 0.5-1.0 mm in size accounted for 38.5 % of the total microplastics in this region. The main microplastic colors were black, white, and transparent, which accounted for 40.75 %, 20.75 %, and 20.38 % of the total microplastics, respectively. There was an increasing trend in the microplastic abundance in sediments in the downstream direction that accompanied the increase in population density from 55.31 persons km-2 upstream to 230.05 persons km-2 downstream. Microplastic pollution was related to the complex geographical, semiarid monsoon climate, elevation, grassland, per capita GDP, and anthropogenic factors in the Yan River basin. The erodible loess and high-intensity rainstorm promoted severe soil erosion, which caused microplastics absorbed in the soil to migrate to the river. Poorly managed solid wastes, such as agricultural mulch, plastic bottles, and other plastic products are also sources of microplastics in the riverbed. This study further clarifies microplastic pollution in typical rivers of highly erosive areas and provides useful information for basin management.

The abundance, characteristics and distribution of microplastics (MPs) in farmland soil-Based on research in China.

Microplastics (MPs) in farmland soil deteriorate soil environment and increase food toxicity, thereby threatening the agricultural production environment and human safety. However, a systematic understanding of MPs pollution in farmland soil is lacking in China. Therefore, the relevant literature was comprehensively discussed to discuss the abundance, characteristics, distribution and influencing factors of MPs in farmland soil. The conclusions are as follows: (1) The highest and lowest MPs abundance were in marginal tropical humid and plateau temperate semi-arid regions, accounting for 7579 n/kg and 48 n/kg, respectively. (2) The main shapes of MPs in farmland soil are fragment/flake and fiber, accounting for 44.0 % and 34.4 %, respectively. The MPs are mostly transparent (21.8 %) and black (21.5 %). Among the MPs types, polyethylene (PE) and polypropylene (PP) are dominant, accounting for 26.2 % and 19.0 %, respectively. The main size of MPs in farmland soil is 0.1-0.5 mm, with average proportions was 51.4 %. (3) Compared with non-fertilizing and non-mulching, the MPs abundance in the fertilizing and mulching farmland soils increased by 170 % and 232 %, respectively. (4) In the farmland soil, the MPs abundance was significantly positive with temperature, sunshine hour, and altitude. (5) In farmland soil of China, the most commonly used MPs dispersion treatment was H2O2 solution digestion, the extracting solution commonly used for density flotation was NaCl solution, and microscopic and spectroscopic measurements were typically used measurements. The results could provide a basis for monitoring the MP abundances in farmland soil and preventing the transfer of MPs pollution in soil.

Distribution of microplastic contamination in the major tributaries of the Yellow River on the Loess Plateau.

Microplastic pollution in rivers had gained increased attention worldwide. However, the differences in microplastic characteristics among major tributaries of large rivers and the environmental factors influencing these characteristics remain uncertain. Through field investigation and indoor experiments, the distribution of microplastics and their driving factors were investigated at 96 sampling sites along the three main tributaries (Huangfuchuan, Wuding and Yan River) of the Yellow River in the Loess Plateau. The results revealed that the average microplastic abundance followed this order: Yan River (430.30 items kg-1) > Wuding River (145.09 items kg-1) > Huangfuchuan River (253.33 items kg-1). The abundance was lower than that in most parts of the world. There was a generally increasing trend in average microplastic abundance from upstream to downstream in the three rivers. The most frequently observed microplastic colors observed were black and white, and the most common polymer type were PE and PS in all three rivers. The dominant shape and size in the three rivers were fiber and particles measuring 0.5-5.0 mm, all accounting for more than half of the total microplastic content. The microplastic abundance, shape, and size were primarily influenced by mean annual precipitation and population density. This relationship can be attributed to the fact that increased population density driven by higher demand and consumption of plastic products, while augmented rainfall aggravated the occurrence of floods and provided conditions for plastic degradation and accumulation. This study will provide fundamental data for pollution assessing and ecological protection of the Yellow River, and provide a certain reference for future management and protection on the Loess Plateau.

Low-cost laser cutting fabricated all-metallic metamaterial near-field focusing lens.

In this work, a low-cost all-metal metamaterial near-field lens based on laser cutting technology is proposed. A novel spiral-slot structure is proposed to achieve miniaturized unit cells with an adjustable 360-degree phase shift at a length smaller than 0.2 times the operating wavelength. Since the unit is entirely constructed of stainless steel, it is resistant to high temperatures and high pressures compared to existing results. Moreover, a four-layer structure is used to increase the transmission coefficient. The final L-band near-field lens is constructed of 20 × 20 units. Simulation and measured results show that the half-power beamwidth of the focus is less than 211 mm from 1.52 GHz to 1.68 GHz at the focal spot observation plane of 500 mm from the lens. Since numerically controlled machine tools and three-dimensional printing are prohibitively expensive for machining large metal components, a low-cost all-metallic lens was manufactured using laser cutting technology. The measured results are in agreement with the simulation results.

Biochar promotes soil organic carbon sequestration and reduces net global warming potential in apple orchard: A two-year study in the Loess Plateau of China.

The Loess Plateau is China's primary apple-growing area, and the orchard is a significant source of greenhouse gases (GHGs) emissions due to high nitrogen fertilizer input. Thus, a two-year field study was carried out to investigate the effects of apple wood derived biochar on GHGs emissions during apple orchard production, including soil organic carbon sequestration (SOCSR) and net global warming potential (NGWP) assessments. There are four treatments in this study: 20 t ha-1 biochar in a non-fertilized plot (B); no biochar in a fertilized plot (F); 20 t ha-1 biochar in a fertilized plot (FB); no biochar in a non-fertilized plot (CK). Results showed that the combined application of biochar and fertilizer stimulated CO2 emissions by 9.25% and 8.39% than either biochar or fertilizer alone. Meanwhile, biochar in fertilized plot increased annual N2O emissions by 32.6% as compared to fertilized plot without biochar amendment. Compared with CK, biochar had no significant effect on GHG emissions in unfertilized plot. The N2O emission factor of FB and F were 0.91% and 0.45% respectively in 2017-2018 and they were both 0.34% in 2018-2019. Moreover, compared with CK, the FB and B treatments increased the SOCSR by 316.52% and 354.78%, while, decreased the NGWP by 368.93% and 480.91%, respectively. Thus, biochar application may help reduce the impact of apple production on climate change by sequestering more soil organic carbon and decreasing the NGWP.

Quantifying the contributions of human activities and climate change to vegetation net primary productivity dynamics in China from 2001 to 2016.

Vegetation is an important component of the terrestrial ecosystem, driven by climate change and human activities. Quantifying the relative contributions of climate change and anthropogenic activities to vegetation dynamics are essential to cope with global climate change. In this paper, the relative contributions of anthropogenic activities and climate change to net primary productivity (NPP) in China were analyzed by a two-step methodology based on the residual trend analysis (RESTREND). Firstly, the unaltered natural vegetation only affected by climate change (Vclimate) and the vegetation affected by climate change and human activities (Vclimate+human) were separated by the multi-temporal land use land cover (LULC) data. Secondly, RESTREND was applied to NPP of Vclimate and Vclimate+human, respectively, to calculate contributions of climatic factors and human activities to vegetation growth. Results revealed that NPP exhibited a significant increase with 3.13 g C m-2 yr-1 from 2001 to 2016 in China. Climate change and human activities both made favorable impacts on vegetation growth during the study period. Besides, with the separation of Vclimate and Vclimate+human, contributions of climatic factors to vegetation changes increased from 1.57 to 1.88 g C m-2 yr-1, with the proportion of 60.06%. While contributions of human activities to NPP decreased from 1.56 to 1.25 g C m-2 yr-1, with the proportion of 39.94%. Moreover, the average contributions of precipitation, temperature, solar radiation, and other climatic factors to NPP over the entire country were 0.72, 0.24, 0.61, and 0.31 g C m-2 yr-1. Precipitation played a decisive role in vegetation changes in arid and semi-arid regions, temperature was the dominant factor for alpine vegetation dynamics, and solar radiation was beneficial to vegetation growth in most areas of China.

[Application of Various Methods to Extract Microplastic from Typical Soils in China].

Microplastics have been found in many environmental systems, such as oceans, terrestrial soils, sediments, and bodies of freshwater. Microplastic pollution in soils has received extensive international attention; however, there is currently no unified standard extraction method. To identify appropriate extraction and component identification methods for microplastics in typical soils in China, samples were identified and their polymer component properties examined using ATR-FTIR(Thermo Nicolet IS 20). The effects of three treatments of water+oil(T1), a saturated NaCl solution+oil(T2), and a saturated NaCl solution(T3) on the detection of four types of microplastics[polyethylene terephthalate(PET), polypropylene(PP), polystyrene(PS), and polyethylene(PE)]in four typical soils(loess, black soil, red soil, and purple soil) were examined. The results showed that:① The extraction rates of the T3 treatment decreased with microplastic density. For PP, PE, and PS, the extraction rates exceeded 86.67%, and the extraction rates of PET were 0%-13.30%. ② The extraction rates of the four kinds of microplastics were 86.67%-100.00% in loess, black soil, and purple soil using the T1 and T2 solutions; however, the residual oil on the surface of microplastics influenced the identification using FTIR. Furthermore, the cleaning effect of PE and PS was poor after wiping with anhydrous ethanol. ③ In red soil, the extraction rates of PET were 56.60% and 50.00% in T1 and T2, respectively; in the T3 treatment, the extraction rates of PET, PE, and PP were 3.33%, 10.00%, and 56.67%, respectively. These results show that the extraction rates of four types microplastics are highest for loess, black soil, and purple soil using T1 and T2, although these two methods need to be combined with anhydrous ethanol cleaning. T3 dispose making the leak of microplastics PET with the density higher than 1 g·cm-3. Methods to extract microplastics from red soils require further research. Overall, this study can inform the investigation and treatment of microplastic pollution in typical regional soils in China.

Influence of Large Reservoir Operation on Water-Levels and Flows in Reaches below Dam: Case Study of the Three Gorges Reservoir.

The Three Gorges Project (TGP) is the world's largest water conservation project. The post-construction low-flow water level at the same discharge below the dam has declined, but there remains disagreement over whether the flood level has increased. Measured water levels and upstream and downstream flow data from 1955 to 2016 show that, post-construction: (1) the low-flow water level at the same discharge decreased, and the lowest water level increased due to dry-season reservoir discharge; (2) the decline of the low-flow water level below the dam was less than the undercutting value of the flow channel of the river; (3) the flood level at the same discharge below the dam was slightly elevated, although peak water levels decreased; (4) flood characteristics changed from a high discharge-high flood level to a medium discharge - high flood level; and (5) an expected decline in the flood level downstream was not observed. Channel erosion and the adjustment of rivers and lakes tend to reduce flood levels, while river bed coarsening, vegetation, and human activities downstream increase the flood level. Although the flood control benefits of the Three Gorges Dam (TGD) and the upstream reservoirs are obvious, increased elevation of the downstream flood level remains a concern.

Windage Heating in a Shrouded Rotor-Stator System.

This paper has experimentally and numerically studied the windage heating in a shrouded rotor-stator disk system with superimposed flow. Temperature rise in the radius direction on the rotating disk is linked to the viscous heating process when cooling air flows through the rotating component. A test rig has been developed to investigate the effect of flow parameters and the gap ratio on the windage heating, respectively. Experimental results were obtained from a 0.45 m diameter disk rotating at up to 12,000 rpm with gap ratio varying from 0.02 to 0.18 and a stator of the same diameter. Infrared temperature measurement technology has been proposed to measure the temperature rise on the rotor surface directly. The PIV technique was adapted to allow for tangential velocity measurements. The tangential velocity data along the radial direction in the cavity was compared with the results obtained by CFD simulation. The comparison between the free disk temperature rise data and an associated theoretical analysis for the windage heating indicates that the adiabatic disk temperature can be measured by infrared method accurately. For the small value of turbulence parameter, the gap ratio has limited influence on the temperature rise distribution along the radius. As turbulence parameter increases, the temperature rise difference is independent of the gap ratio, leaving that as a function of rotational Reynolds number and throughflow Reynolds number only. The PIV results show that the swirl ratio of the rotating core between the rotor and the stator has a key influence on the windage heating.