互助资金政策对贫困村劳动力流动的影响--基于5省10县准实验研究的DID分析

促进贫困地区农村劳动力向外流动是提高农民收入、缩小城乡差距的关键。在农村劳动力尤其是贫困劳动力外流增速放缓的背景下,文章从信贷约束缓解的视角出发,基于5省10县互助资金监测的准实验研究项目,借助双重差分(DID)模型,利用1059个微观农户的三期面板数据,从家庭层面考察了互助资金政策对贫困村劳动力流动的影响,并从缓解流动性约束、资本替代劳动和提供隐性担保三个角度对作用机制进行了分析和检验。研究结果表明:①互助资金政策的实施对贫困村劳动力外流具有显著的促进作用。安慰剂检验和稳健性检验进一步加强了研究结论的可靠性。②缓解农户的流动性约束是互助资金促进贫困村劳动力外流的路径之一,通过向农户提供借款,使农户尤其是贫困农户获得了满足迁移成本的金融资源,从而促进了向外流动。③资本替代劳动的机制作用并不明显,这可能与互助资金借款额度有限有关,无法满足农户机械化的资本需求。④为农户家庭面临的收入风险提供隐性担保也是互助资金促进贫困村劳动力外流的路径之一,通过为农户提供资金融通渠道,确保农户即使在外流失败的情况下能够通过向互助资金借贷平滑消费和缓解风险冲击。研究结论为探索农村金融供给能否成为进一步促进剩余贫困劳动力转移的契机提供了有理论价值和可操作的视角,未来应继续坚持农村金融改革的步伐,加快金融产品和金融工具创新,不断提高贫困农户的信贷可得性和可持续性收益。     

山岳景区依托型乡村旅游就业吸附的空间特征

乡村振兴战略和乡村产业转型发展背景下,休闲旅游产业在乡村地域的兴起扰动了当前就业人口由乡村向城镇流动的宏观趋势,乡村旅游就业吸附正从微观上改变着城乡间劳动力空间流动的格局和过程。为科学理解乡村旅游就业吸附引起城乡劳动力空间流动发生变化的特征与机制,文章基于在浙晋山岳景区依托型乡村旅游地深度访谈的一手数据,分析了乡村旅游就业人口流动的空间分布特征、就业吸附的空间模式和过程机制。结果表明:①山岳景区依托型乡村旅游就业吸附呈现距离衰减和空间层级结构的特征,0~4 km为核心层、4~12 km为过渡层、12 km以上为外缘层;但在不同社会经济发展环境下该特征存在区域差异,欠发达地区乡村旅游就业吸附的空间集中性,比发达地区更加明显。②研究从城乡地域空间系统的视角,基于人口转移“推—拉”理论对乡村旅游就业人口空间流动特征和影响机制进行分析,发现山岳景区依托型乡村旅游就业吸附呈现以城镇、乡村为就业吸附极,以城乡接合部为吸附效用“分水岭”的空间模式;其中,连接城乡间的便捷交通是乡村旅游就业吸附实现的关键介质。③基于乡村旅游就业吸附空间适用性,文章针对性提出了“空间围栏效应”的概念。文章不仅从微观尺度上丰富了乡村旅游就业人口空间流动特征、过程、模式等的理论认识,而且对切实指导乡村地域在乡村旅游开发实践中理性理解乡村旅游的就业促进作用,提升乡村旅游开发规划和投资的效率具有积极意义。     

Patterns of plant trait-environment relationships along a forest succession chronosequence

Land-use change due to socioeconomic factors leads to the abandonment of traditional intensive coppice management in large areas of the mountainous landscapes of the Apennines (Italy). In this study we explored the multivariate relationship between plant species traits, stage of forest succession and environmental gradients. We focused on community-level patterns in plant traits of the vegetation of beech forest understory along the regeneration chronosequence initiated after cessation of coppicing. We hypothesized that the correlations between the traits and environmental factors should increase with succession age due to the decreasing role of chance.Landscape-level heterogeneity, i.e. changing elevation, slope, exposition, bedrock and forest stand age was assessed using a stratified random sampling design. Sixty sites were sampled for stand structure and species composition. We focused on 14 plant traits related to persistence, growth and dispersal. The recently developed data-analytical method, Model-Based Recursive Partitioning, was used to disentangle the relationships between patterns of plant traits and environmental gradients.About half (seven) of the studied plant traits showed significant correlations with succession stand age, elevation, inclination, heat index and bedrock. Contrary to the low number of trait-environment correlations in early succession, eight traits showed significant relationships with one or more abiotic factors in older stages of the post-coppice development. Stand age had the highest independent explanatory power, explaining 40% of variance of SLA, more than 17% of variance of short-distance seed dispersal and more than 15% of variance of both long-term connection and extensive perennial root. Among the other abiotic factors, elevation explained 27% of variance of SLA, inclination explained 6-8% of variance of long-term connection, extensive perennial root, thickening and large bud bank.The observed trait-environmental relationship is assumed to be driven by various environmental factors operating at various levels of complexity. While forest succession in relatively homogeneous landscapes might be driven mainly by environmental factors related to forest succession itself and associated abiotic changes (such as changes in light and soil moisture patterns), in heterogeneous landscapes the succession pathways may be structured by landscape-level environmental factors such as inclination. However, in the present study, forest stand age had the highest explanatory power for most of the investigated traits, supporting the assumption of the overall strong impact of succession-driven environmental factors in trait-environment relationships.     

Managed grassland alters soil N dynamics and N2O emissions in temperate steppe

Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen(N) dynamics and nitrous oxide(N_2O) emissions. However, it remains unclear how large-scale grassland reclamation will impact the grassland ecosystem as a whole. Here, we investigated the effects of the conversion from native to managed grasslands on soil N dynamics and N_2O emissions by field experiments in Hulunber in northern China. Soil(0–10 cm), nitrate(NO_3~-),ammonium(NH_4~+), and microbial N were measured in plots in a temperate steppe(Leymus chinensis grassland) and two managed grasslands(Medicago sativa and Bromus inermis grasslands) in 2011 and 2012. The results showed conversion of L. chinensis grassland to M.sativa or B. inermis grasslands decreased concentrations of NO_3~–-N, but did not change NH_4~–N . Soil microbial N was slightly decreased by the conversion of L. chinensis grassland to M.sativa, but increased by the conversion to B. inermis. The conversion of L. chinensis grassland to M. sativa(i.e., a legume grass) increased N_2O emissions by 26.2%, while the conversion to the B. inermis(i.e., a non-legume grass) reduced N_2O emissions by 33.1%. The conversion from native to managed grasslands caused large created variations in soil NO?3~-+–N and NH_4~–N concentrations. Net N mineralization rates did not change significantly in growing season or vegetation type, but to net nitrification rate. These results provide evidence on how reclamation may impact the grassland ecosystem in terms of N dynamics and N_2O emissions.     

Application of an aerosol electrical mobility spectrum analyzer: Charged-particle polarity ratio measurement in the Antarctic and Arctic regions

An aerosol electrical mobility spectrum analyzer (AEMSA), developed at Hanyang University, was employed to investigate the particle charge characteristics in the Antarctic and Arctic regions. The particle charge characteristics in these areas were compared with the charging state in Ansan, South Korea, located in the midlatitude, where artificial factors, such as human activity, urbanization, and traffic, might result in a higher total concentration. Furthermore, in Ansan, South Korea, the charged-particle polarity ratio was very stable and was close to 1. However, notably different particle charge characteristics were obtained in the Antarctic and Arctic regions. The imbalance between the numbers of positively and negatively charged particles was evident, resulting in more positive charges on the atmospheric particles. On average, the positively charged particle concentrations in the Antarctic and Arctic areas were 1.4 and 2.8 times higher, respectively, compared with the negatively charged particles. The developed AEMSA system and the findings of this study provide useful information on the characteristics of atmospheric aerosols in the Antarctic and Arctic regions and can be further utilized to study particle formation mechanisms.     

污染土壤中重金属的优势流迁移

用亮蓝溶液染色鉴定了2个污染土壤的优势流途径,并分离和采集被染色剂染色和不染色的土样,分析了重金属(Cu,Pb,Cd)含量和形态．结果表明,心土层以下染色部分土壤的重金属含量明显高于不染色部分土壤．两之间的差异随土壤污染程度的增加而增加．染色部分土壤中酸溶态和有机质结合态重金属的比例明显高于不染色部分的土壤．染色部分土壤的细粘粒与粘粒总量的比值也高于非染色部分土壤,但供试土壤的水溶性重金属含量很低,推测颗粒态重金属的迁移是重金属迁移的主要方式,优势流可能在土壤重金属垂直迁移中有重要的作用．     

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH₂OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl₂ extractable fraction. A large proportion of Cu was bound to the acidic H₂O₂ extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier’s procedure, and the order of mobility was Zn > Cd > Cu  > Pb.     

Behavior of bensulfuron-methyl in an agricultural alkaline soil

A field experiment to determine the available bensulfuron-methyl (BSM) in the upper soil layer was conducted in an agricultural area in the South of Spain. To facilitate herbicide analysis, two application rates were employed, 200 g ha^?1 and 5 kg ha^?1. Samples of upper soil and soil solution were collected. Soil solution was sampled by means of metallic samplers, placed at a depth of 35 cm. In the plots receiving the lower dose ceramic suction, porous cups were also installed. Results from soil solution samples showed that the maximum BSM concentration was found after 8-10 days for the high irrigation supply (945 mm) and after 18-25 days for the lower irrigation regime (405 mm). The mathematical model FOCUSPELMO 1.1.1 was applied to interpret the data obtained in the field experiments. In general, there was a reasonable agreement between experimental and simulated data for soil samples, although the model did not acceptably predict herbicide concentrations in water soil samples. Ceramic cups sampled a higher soil water volume and more frequently than did the metallic samplers. However some variable results were attributed to preferential flow.     

Comparative sorption,desorption and leaching potential of aminocyclopyrachlor and picloram

Sorption and desorption of aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropylpyrimidine-4-carboxylic acid) were compared to that of the structurally similar herbicide picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) in three soils of differing origin and composition to determine if picloram data is representative of aminocyclopyrachlor behavior in soil. Aminocyclopyrachlor and picloram batch sorption data fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram (1/n = 0.80–0.90). Freundlich sorption coefficients (K _f) for aminocyclopyrachlor were lowest in the eroded and depositional Minnesota soils (0.04 and 0.12 μmol ^(1–1/n) L^1/n kg^?1) and the highest in Molokai soil (0.31 μmol ^(1–1/n) L^1/n kg^?1). For picloram, K _f was lower in the eroded (0.28 μmol ^(1–1/n) L^1/n kg^?1) as compared to the depositional Minnesota soil (0.75 μmol ^(1–1/n) L^1/n kg^?1). Comparing soil to soil, K _f for picloram was consistently higher than those found for aminocyclopyrachlor. Desorption of aminocyclopyrachlor and picloram was hysteretic on all three soils. With regard to the theoretical leaching potential based on groundwater ubiquity score (GUS), leaching potential of both herbicides was considered to be similar. Aminocyclopyrachlor would be ranked as leacher in all three soils if t_1/2 was > 12.7 days. To be ranked as non-leacher in all three soils, aminocyclopyrachlor t_1/2 would have to be <3.3 days. Calculated half-life that would rank picloram as leacher was calculated to be ～15.6 d. Using the current information for aminocycloprachlor, or using picloram data as representative of aminocycloprachlor behavior, scientists can now more accurately predict the potential for offsite transport of aminocycloprachlor.     

杭州市超细微粒数浓度和粒径分布特征

应用FMPS(fast mobility particle sizer)对杭州市城区和城郊工业园区超细微粒的数浓度及粒径分布进行现场跟踪测量,并对数据进行分析.结果表明:杭州市大气超细微粒在5～500 nm内,主要呈对数双峰分布,峰值粒径多处在10～50 nm间.城郊工业园区的平均总数浓度最高,达4.11×104 cm-3,最高值出现在中午,而城区的峰值粒径区间整体右移,表明超细微粒污染较轻.超细微粒数浓度在上午和下午的上、下班期间出现不同程度上升,夜间浓度普遍降低,但偶有波动.部分工厂有夜间工作情况,故夜晚空气质量的下降也应引起重视.