城乡劳动力流动及其对农地利用影响研究评述

农业劳动力务农机会成本呈上升趋势,促使大量农业劳动力向城镇流动,成为当今中国社会的一个突出特征。劳动力城乡流动会影响农户的土地利用决策行为,继而影响土地利用变化过程。为理解这一过程对于农地利用变化的影响,文章首先综述了城乡劳动力流动理论研究的历史脉络,并总结了国内外劳动力流动对农地利用影响的研究进展。提出了尚需研究的若干学术问题,即在方法上需要建立劳动力流动-农户土地利用决策模型,重视农户尺度研究,注重区域差异。     

Perfluorooctane sulfonate promotes the migration of colorectal cancer cells by inducing epithelial-mesenchymal transition

The potential association between colorectal cancer(CRC)and environmental pollutants is worrisome.Previous studies have found that some perfluoroalkyl acids,including perflu-orooctane sulfonate(PFOS),induced colorectal tumors in experimental animals and pro-moted the migration of and invasion by CRC cells in vitro,but the underlying mechanism is unclear.Here,we investigated the effects of PFOS on the proliferation and migration of CRC cells and the potential mechanisms involving activating the PI3K/Akt-NF-κB signal pathway and epithelial-mesenchymal transition(EMT).It was found that PFOS promoted the growth and migration of HCT116 cells at non-cytotoxic concentrations and increased the mRNA ex-pression of the migration-related angiogenic cytokines vascular endothelial growth factor(VEGF)and interleukin-8(IL-8).In a mechanistic investigation,the up-stream signal path-way PI3K/Akt-NF-κB was activated by PFOS,and the process was suppressed by LY294002(PI3K/Akt inhibitor)and BAY11-7082(NF-κB inhibitor)respectively,leading to less prolif-eration of HCT116 cells.Furthermore,matrix metalloproteinases(MMP)and EMT-related markers were up-regulated after PFOS exposure,and were also suppressed respectively by LY294002 and BAY11-7082.Moreover,the up-regulation of EMT markers was suppressed by a MMP inhibitor GM6001.Taken together,our results indicated that PFOS promotes colorec-tal cancer cell migration and proliferation by activating the PI3K/Akt-NF-κB signal pathway and epithelial-mesenchymal transition.This could be a potential toxicological mechanism of PFOS-induced malignant development of colorectal cancer.     

库布齐沙漠典型地区景观变化研究

Spatial pattern analysis is the core component in landscape ecology research. We analyzed the landscape pattern and dynamic process of the Kubuqi Desert by using a typical region as a study area. This study area includes four towns: ShuLinZhao, WangAiZhao, BaiNiJing and JiGeSiTai. The area of cropland, fixed sand dune, woodland, residential area and wetland increased and centralized gradually, while the area of semi-fixed sand dune, drifting sand dune, meadow and washland decreased and dispersed gradually from 1987 to 2003. On the landscape level, the patch shape tended to be regular, and the landscape pattern tended to be simple, causing the fragmentation degree, heterogeneity and diversity of the landscape to decrease. Fixed sand dune, Semi-fixed sand dune, drifting sand dune, meadow and river flood plains were the five main export classes, and residential area, cropland and wetland were the three main import classes. The classes that had a relatively large total area and large average patch area had a smaller extent of gravity center migration, whereas the classes with small total area and small average patch area had a larger extent of gravity center migration; this is because the small patches are easily influenced by human activities or natural factors. In addition, the desertification area and desertification degree reduced gradually in the study area during the period from 1987 to 2003.     

基于FBM法追踪秦皇岛海域赤潮迁移扩散

在Delft3D-FLOW模型模拟水动力的基础上,基于FBM粒子追踪法建立和验证赤潮迁移扩散模型.模拟了秦皇岛海域潮流和风生流,分析了风生流对赤潮迁移扩散的作用,对比分析了FBM法、拉格朗日法和常规布朗运动法在赤潮迁移扩散模拟中的特性,测试了模型Hurst指数的敏感性并得出其在赤潮模拟中的合理取值范围.主要结论为：①秦皇岛海域的赤潮主要随潮流的涨落而往复移动,一个涨落潮周期内赤潮的净迁移距离较小;②秦皇岛海域夏季潮流较弱,但风对赤潮迁移具有一定影响,易产生东北向风生流,导致赤潮更易往东北方向迁移;③Hurst指数较明显地影响粒子云的扩散范围,Hurst指数取0.80±0.03能比较真实地模拟秦皇岛海域赤潮的迁移扩散;④FBM法可模拟赤潮的non-Fickian扩散现象,使其模拟的粒子云扩散范围和分布形状明显优于拉格朗日法和常规布朗运动法.     

傍河开采驱动下潜流带氮素迁移转化的生物地球化学特征

为研究傍河开采驱动下潜流带中\"三氮\"迁移转化规律和氧化还原分带,通过不同时期在傍河开采条件下采集潜流带土样和水样分析三氮的转化过程及特性,并结合溶解氧和氧化还原电位及硝酸根和亚硝酸根含量和优势菌来判断其迁移转化规律与机理。结果表明：河水在入渗的过程中,首先进入处于离岸-6~1.5 m处的氧化带,O2与有机物发生反应释放出CO2,随后到离岸1.5~17 m处的弱氧化环境的氧化还原过渡带,在硝化细菌和反硝化菌的作用下发生硝化反应和反硝化反应,最后到离岸17~350 m处缺氧环境的还原带中,在缺氧条件下反硝化反应。优势菌对水源地氧化还原作用分带具有响应联系特征。枯水期水位低能够更加快速降低水中溶解氧DO、氨氮、硝酸盐氮,所以枯水期的氧化还原距离短,丰水期的距离稍长。在傍河开采驱动下,水动力条件随着不同时期发生改变,河水向地下水补给过程中各方面均存在差异,而这一系列的差异影响了氮素在地下介质中的迁移转化。     

Human appropriation of net primary production as determinant of avifauna diversity in Austria

The relationship between land-use induced changes in production ecology and avifauna diversity was analysed using a GIS land cover dataset on a 0.25 km × 0.25 km grid covering Austria's national territory. Considering only aboveground processes, the “human appropriation of net primary production” (HANPP = potential NPP − NPP_t), actual NPP (NPP_act), harvest (NPP_h) and NPP_t (= NPP_act − harvest) were recalculated based on existing datasets. Elevation as well as indicators of land cover heterogeneity and landscape heterogeneity were also considered. Correlation analyses were performed between these potential determinants of avifauna diversity and breeding bird species richness data as well as the percentage of endangered breeding birds included in the Austrian red list. Four spatial scales—0.25 km × 0.25 km, 1 km × 1 km, 4 km × 4 km and 16 × 16 km, were analysed. It was shown that breeding bird species richness was more strongly correlated with production ecological indicators and elevation than with heterogeneity indicators. A residual analysis in which the effect of elevation (a proxy for climate) on species richness and its potential determinants was removed confirmed the importance of the availability of trophic energy (NPP) for bird diversity patterns. The results support the species-energy hypothesis, thus confirming the notion that HANPP could be a useful pressure indicator for biodiversity loss.     

腐殖酸及酸雨对贫铀在土壤中迁移的影响研究

 利用经过完善的贫铀迁移模型,研究腐殖酸(HA)及酸雨对贫铀在土壤中迁移的影响.结果表明,对照组(北京地区土壤)DU迁移到达9~11cm,分别添加2%、5%、10%HA的实验组DU迁移依次降低,分别为21~23cm、15~17cm、11~13cm,说明腐殖酸促进了DU迁移; pH值为4.0和3.0的模拟酸雨,分别使贫铀迁移至29~31cm及35cm以上,说明酸雨促进了贫铀迁移;在酸雨和腐殖酸综合作用下贫铀迁移仅到5~7cm,说明腐殖酸和酸雨综合作用抑制了贫铀迁移.     

环境中的轮胎磨损颗粒:从路面到海洋

轮胎磨损颗粒是环境中微塑料的主要来源之一,目前全球轮胎磨损颗粒的释放量在590万t·a-1左右,约占海洋微塑料总量的15％.轮胎磨损颗粒产生于路面,通过雨水径流迁移,进而存在于路面、土壤、沉积物、水体、生物体等环境介质中.当前轮胎磨损颗粒的检测主要通过检测标记物来实现,因此,标记物的选择是关键.同时,轮胎磨损颗粒会通过...     

胶州湾表层沉积物黏土矿物分布特征及物源分析

多溴联苯醚对海洋生物生长甚至人体健康危害较大,然而,我国近海多溴联苯醚的迁移转化及调控机制尚不明确。本文利用数值模型定量分析了胶州湾多溴联苯醚-153（polybrominated diphenyl ethers 153,BDE-153）的季节性迁移转化过程。模拟结果表明：胶州湾BDE-153浓度的季节变化呈现明显的夏季单峰分布特征,溶解态和总颗粒态BDE-153的最高浓度分别为0.22 μg/m³和2.3 μg/m³;浮游植物吸收、死亡以及碎屑矿化过程中的BDE-153转化速率同样在夏季明显高于其他季节。胶州湾BDE-153浓度及其在生化过程中的转化速率均呈自北向南带状衰减规律,尤其在西北角的大沽河和东北角的墨水河入海口附近数值最高。河流是胶州湾BDE-153的关键来源,其入海速率为10.5 kg/a,明显高于海气交换的补给速率。与外海的对流交换是胶州湾BDE-153的主要汇,溶解态和总悬浮颗粒态的输出速率分别为1.1 kg/a和8.0 kg/a。