南汇边滩的沉积特征和沉积物输运趋势

在对南汇边滩沉积物粒度特征进行分析的基础上,利用Gao Collins泥沙概率输运模型探讨边滩的沉积物输运趋势,结果表明：①沉积物中值粒径、分选系数和偏度的分布具有一致性,三者相关性较强;②边滩的沉积物粒度特征表现为正偏,分选性较差,分选系数值集中在2左右,沉积物相对较粗（中值粒径大于0.01 mm）的区域主要集中在没冒沙中部、南汇咀及卢潮港近岸,其它区域沉积物相对较细（中值粒径小于0.01 mm）;③将 Gao Collins的泥沙概率模型和南汇边滩的动力与沉积环境结合表明,沉积物在东滩的净输运趋势是由北向南输运。由于南滩的动力条件相对复杂,因此南滩沉积物的净输运趋势有待进一步分析。     

农地流转背景下地块规模对农户种粮投入影响分析

近年来粮食安全受到国家和社会的广泛关注,农地投入作为粮食生产的重要要素,是保障粮食稳定产出的前提。学者就农地规模对农户种粮投入的影响已进行了较多研究,但受农地流转的影响,土地要素更具多样化,土地规模与农户种粮投入的关系发生变化。随着农地流转在我国的快速发展,探析农地流转影响下土地规模对农户种粮投入影响的变化成为一个亟待研究的问题,对保障国家粮食安全具有重要意义。考虑到地块的异质性,本文基于山东、河南、安徽三个粮食主产省622户农户1 284个地块的粮食生产数据从村庄和农户两个层次控制了生产要素市场价格、地块要素等非主观因素,进行多层模型回归分析。结果表明,农地流转特征及地块特征对农户粮食生产单位面积投入有显著影响。地块规模和转入地占比对农地投入影响为负,转入地占比越大,地权稳定性越低,农户投入积极性受到挫伤越明显,在转入地上的投入减少。随着转入土地面积的增加,农户从事粮食生产的机会成本增大,使其有更强的动力增加种粮投入,地块规模的负向影响程度降低。基于分析结果,本文得出以下3点结论:(1)规模化经营有利于降低单位面积种粮成本;(2)农地流转发生时,地块规模对种粮投入的影响发生改变,成片规模化经营将成为我国粮食生产的必然趋势;(3)提高土地综合条件可以降低投入成本,并提高农户投入积极性。要保障国家粮食安全,需从降低种粮成本、提高农户收益着手,建议鼓励农村土地流转,推动粮食规模化生产,同时也要注重增加财政拨款,建设高标准粮田,强化高标准粮田的农业基础设施建设,完善田间配套工程。     

湖北郧西县庹家湾剖面粒度组成特征及其环境意义

对湖北省郧西县庹家湾(TJW)剖面的地层序列、年代、磁化率及粒度组成进行研究。结果表明:TJW剖面具有表土(MS)→全新世黄土(L0)→古土壤(S0)→过渡层(Lt)→马兰黄土(L1)→黄土与砂互层(T1-al2)→砾石层(T1-al1)的地层序列;在马兰黄土层上部的黏粒含量、黏粒/粉砂值以及磁化率值明显高于典型马兰黄土,而接近古土壤(S0),其成壤作用明显,属于较典型的弱古土壤层(L1-S1和L1-S2),其年龄在27.3~21.6 ka B.P.之间。此现象反映了在汉江上游地区,晚更新世时期的冰期气候并不是持续稳定的,在27.3~21.6 ka B.P.期间存在相对短暂的温暖湿润阶段,这次气候事件可与黄土高原地区进行良好对比。     

Secondary arsenic minerals in the environment: A review

Information on arsenic (As) speciation in solid materials is critical for many environmental studies concerned with As stability and/or mobility in natural As-impacted soils and mining or industrial sites contaminated by As. The investigation of these systems has provided evidence for a number of secondary As minerals that have often played a significant role in As mobility in the solid phase–water system. This paper presents a list of environmentally important secondary As minerals in contaminated soil and waste systems, summarizes the information about their origin, occurrence, environmental stability and thermodynamics, and proposes several important avenues for further investigation.     

长江口及其邻近海域表层沉积物分布特征

根据长江口和杭州湾北部沉积物粒度分析数据,研究表层沉积物类型、分布以及分区特征。结果表明：沉积物的分布特征受水动力条件、地貌类型以及泥沙来源等因素的综合影响,长江口表层沉积物在纵向分布上,自西向东粒径从粗到细、分选程度从好至差,在横向上自北港－北槽－南槽,沉积物粒度逐渐变细;水流动力作用强的河槽和波浪作用强的口门浅滩沉积物粒度较粗,水动力较弱的河口边滩及口外海滨区沉积物则较细。根据沉积物分布特征可将长江口及其邻近海域分为河口分汊河段沉积区、河口拦门沙沉积区、口外海滨沉积区和杭州湾北部沉积区等4个沉积区。     

烟草烟雾对室内空气颗粒物浓度的影响

采用电称冲击低压系统(ELPI)将无烟室和吸烟室内的空气颗粒物(0.03～10.00 μm)分成12级,对其粒子数和质量浓度进行测定.结果表明,吸烟室PM0.03～10.00的日平均粒子数和质量浓度分别是无烟室的1.50、1.13倍.烟草烟雾对室内颗粒物粒子数的影响集中在0.03～1.00 μm粒径段;对室内颗粒物质量浓度的影响表现为双模态结构,峰值分别在0.20～0.70、5.00～8.20 μm粒径段.烟草烟雾颗粒物的粒子数和质量浓度随烟雾消散时间的增加而减少,粒径越小,减小的越明显;烟草烟雾颗粒物在室内消散缓慢,会在长时间内造成影响,应引起足够关注.     

Approximating the distribution of recreational visits from on-site survey data

While convenient and often used, on-site surveys are biased by the fact that users who visit the site more often are proportionately more likely to be sampled. This so-called avidity or size biased sampling results in over-estimating the visitation patterns of the average user. This analysis develops a rule of thumb method that may easily be applied by recreation site managers to visitation data collected on-site in order to infer behavior of the average user of the site. The key assumption that drives the derivation is that the visitation data of users is logarithmically distributed. To evaluate the methodology, we analyze several data sets of recreational users assuming that they reflect the populations of users and from these construct hypothetical on-site samples.     

Vertical distribution of anthropogenic radionuclides in cores from contaminated floodplains of the Yenisey River

The Mining and Chemical Industrial Combine, Zheleznogorsk (MCIC, previously known as Krasnoyarsk-26) on the River Yenisey has contaminated the surrounding environment with anthropogenic radionuclides as a result of discharges of radioactive wastes. The purpose of this study was to investigate the vertical distribution of anthropogenic contamination (¹³⁷Cs and plutonium) within floodplain areas at different distances from the discharge point. Sites were chosen that display different characteristics with respect to periodic inundation with river water. Cs-137 activity concentrations were in the range 23–3770 Bq/kg (dry weight, d.w.); Pu-239,240 activity concentrations were in the range <0.01–14.2 Bq/kg (d.w.). Numerous sample cores exhibited sub-surface maxima which may be related to the historical discharges from the MCIC. Possible evidence indicating the deposition of earlier discharges at MCIC in deeper core layers was observed in the ²³⁸Pu:^239,240Pu activity ratio data: a Pu signal discernible from global fallout could be observed in numerous samples. Cs-137 and Pu-239,240 activity concentrations were correlated with the silt fraction (% by mass <63 μm) though no significant correlation was observed between (grain-size) normalised ¹³⁷Cs activity concentrations and distance downstream from the MCIC.     

Particle-size-fractioned transfer of dioxins from sediments to water columns by resuspension process

Particle-size-fractioned transfer of dioxins from sediments to water columns by resuspension process was investigated, using supernatant samples obtained from shaking experiments of sediment-water pairs simulating natural disturbances. The concentrations (dry-matter mass basis) of individual compounds (Cfraction) in two particle size fractions (0.1-1 and 1-10 μm) in the supernatants were generally slightly higher than those in the original sediment (Csed). Cfraction/Csed ratios ranged from 0.45 to 5.9 (median 1.5) without consistent differences among congener groups or consistent correlations against the number of chlorine atoms. The dioxin concentrations in the water column associated with the remaining sediment particles can therefore be estimated by those in the original sediment and by the concentration of suspended sediment particles in the water. The concentration of each compound in the remaining sediment particles (mostly 0.1-10 μm in size) can be roughly estimated by multiplying the concentration in the original sediment by 1.5.     

垃圾填埋场微生物气溶胶粒径分布研究

为了了解垃圾填埋场微生物气溶胶粒径分布规律,在北京市某垃圾卫生填埋场填埋区、渗滤液处理区、生活区分别选定监测点,利用安德森六级微生物采样器,对填埋场空气微生物进行了系统的定点取样、测定和分析。研究结果表明,空气细菌粒径分布均为第Ⅰ级(>8.2 μm)最高,填埋区空气细菌粒径呈偏态分布,渗滤液处理区、生活区分别在第Ⅳ级和第Ⅲ级出现第2个峰值。携带细菌的可吸入微粒在渗滤液处理区比例最大。空气真菌与放线菌均在第Ⅳ级分布最高,携带真菌和放线菌的可吸入粒子的比例显著大于细菌(P<0.05)。填埋区不同作业时段空气微生物粒径在各级分布比例基本一致。填埋区细菌气溶胶中值直径为5.7 μm,渗滤液处理区为3.7 μm,生活区为5.3 μm,显著大于真菌气溶胶和放线菌气溶胶的中值直径(P<0.05)。