A high-resolution sedimentary archive from landslide-dammed Lake Mengda,north-eastern Tibetan Plateau

Lacustrine sediments have been widely used to investigate past climatic and environmental changes on millennial to seasonal time scales. Sedimentary archives of lakes in mountainous regions may also record non-climatic events such as earthquakes. We argue herein that a set of 64 annual laminae couplets reconciles a stratigraphically inconsistent accelerator mass spectrometry (AMS) ¹⁴C chronology in a ~4-m-long sediment core from Lake Mengda, in the north-eastern Tibetan Plateau. The laminations suggest the lake was formed by a large landslide, triggered by the 1927 Gulang earthquake (M = 8.0). The lake sediment sequence can be separated into three units based on lithologic, sedimentary, and isotopic characteristics. Starting from the bottom of the sequence, these are: (1) unweathered, coarse, sandy valley-floor deposits or landslide debris that pre-date the lake, (2) landslide-induced, fine-grained soil or reworked landslide debris with a high organic content, and (3) lacustrine sediments with low organic content and laminations. These annual laminations provide a high-resolution record of anthropogenic and environmental changes during the twentieth century, recording enhanced sediment input associated with two phases of construction activities. The high mean sedimentation rates of up to 4.8 mm year^?1 underscore the potential for reconstructing such distinct sediment pulses in remote, forested, and seemingly undisturbed mountain catchments.     

Dating of two thermokarst lakes in Beiluhe Basin,Qinghai-Tibetan Plateau

Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain their age.We obtained lake-bottom samples of 50 cm length from lake BLH-A and 25 cm length from lake BLH-B.Environmental 137 Cs and 210 Pb and radiocarbon age dating techniques were applied to the 50 cm and 25 cm samples,respectively.The results indicate that the initiation of BLH-A is about 800-900 a B.P.,and approximately 1,450±30 a B.P.to 2,230±30 a B.P.for BLH-B.These results will provide scientific bases for sedimentological study and thermokarst activity in Beiluhe Basin.     

Advances in studies on concrete durability and countermeasures against freezing-thawing effects

This paper is a meta-analysis of recent domestic and foreign research on freezing-thawing effects on concrete durability. The main theories on the mechanisms of freeze-thaw damage to concrete are introduced： the hydrostatic pressure theory, the osmotic pressure theory, the critical water saturation degree theory, the dual mechanism theory, and the micro-ice-crystal lens model theory. The influence laws of freezing-thawing on the mechanical properties of concrete are summarized, and countermeasures to improve concrete durability in freezing-thawing circumstances are presented. This work provides valuable references for future engineering constructions in cold regions.     

Land use effects on soil organic carbon,microbial biomass and microbial activity in Changbai Mountains of Northeast China

Land use changes are known to alter soil organic carbon （SOC） and microbial properties, however, information about how conversion of natural forest to agricultural land use as well as plantations affects SOC and microbial properties in the Changbai Moun- tains of Northeast China is meager. Soil carbon content, microbial biomass carbon （MBC）, basal respiration and soil carbon mineraliza- tion were studied in five selected types of land use： natural old-growth broad-leaved Korean pine mixed forest （NF）; spruce plantation （SP） established following clear-cutting of NF; cropland （CL）; ginseng farmland （GF） previously under NF; and a five-year Mongolian oak young forest （YF） reforested on an abandoned GF, in the Changbai Mountains of Northeast China in 2011. Results showed that SOC content was significantly lower in SP, CL, GF, and YF than in NF. MBC ranged from 304.4 mg/kg in CL to 1350.3 mg/kg in NF, which was significantly higher in the soil of NF than any soil of the other four land use types. The SOC and MBC contents were higher in SP soil than in CL, GF, and YF soils, yielding a significant difference between SP and CL. The value of basal respiration was also higher in NF than in SP, CL, GF, and YF. Simultaneously, higher values of the metabolic quotient were detected in CL, GF, and YF soils, indicat- ing low substrate utilization of the soil microbial community compared with that in NF and SP soil. The values of cumulative mineral- ized carbon and potentially mineralized carbon （Co） in NF were significantly higher than those in CL and GF, while no significant dif- ference was observed between NF and SP. In addition, YF had higher values of Co and C mineralization rate compared with GF. The results indicate that conversion from NF into agricultural land （CL and GF） uses and plantation may lead to a reduction in soil nutrients （SOC and MBC） and substrate utilization efficiency of the microbial community. By contrast, soils below SP were more conducive to the preservation of soil organic matter, which was reflected in the comparison of microbial indicators among CL, GF, and YF land uses. This study can provide data for evaluating soils nutrients under different land use types, and serve as references for the rational land use of natural forest in the study area.     

Valuation of lake and marsh wetlands ecosystem services in China

Wetlands are highly productive natural ecosystems, providing valuable goods and services. There is growing interest in transferring ecosystem service value from the existing wetlands studied to other wetlands ecosystems at a large geographic scale. The benefit transfer method uses the known values from wetlands to predict the value of other wetland sites. This methodology requires only limited time and resources. The present study calculated the value of the ecological services provided by lake and marsh wetlands in China in terms of biodiversity indices, water quality indices and economic indices. Basic data on wetlands were obtained through remote sensing images. The results show that: 1) The total ecosystem service value of the lake and marsh wetlands in 2008 was calculated to be 8.1841 × 1010 United States Dollars(USD), with the marsh and lake wetlands contributing 5.6329 × 1010 and 2.5512 × 1010 USD, respectively. Values of marsh ecosystem service were concentrated in Heilongjiang Province(2.5516 × 1010 USD), Qinghai Province(1.2014 × 1010 USD), and Inner Mongolia Autonomous Region(1.1884 × 1010 USD). The value of the lakes were concentrated in Tibet Autonomous Region(6.223 × 109 USD), Heilongjiang(5.810 × 109 USD), and Qinghai(5.500 × 109 USD). 2) Waste treatment and climate regulation services contributed to 26.29% and 24.74% respectively, of the total ecosystem service value of the marsh wetlands. Hydrological regulation and waste treatment contributed to 41.39% and 32.75%, respectively, of the total ecosystem service value of the lake wetlands. 3) The total ecological service value of the lake and marsh wetlands was 54.64% of the total service value of natural grassland ecosystems and 30.34% of the total service value of forests ecosystems in China.     

孤立金属尖端的电晕触发阈值

为了得到金属尖端在发生电晕放电时尖端处的电场强度,该文首先采用实验室实验得到不同高度、不同形状、不同材质的金属尖端发生电晕放电时的环境电场阈值;再采用有限元法计算二维泊松方程,得到尖端处电晕触发阈值,由此得出以下结论:环境电场阈值随金属尖端高度的增大基本呈线性减小趋势,随着尖端越来越尖,环境电场阈值呈先减小后增大的变化趋势;高度、形状对金属物尖端处电晕触发阈值无影响,尖端处电晕阈值为定值;给出尖端处电晕触发阈值为158.75 kV·m-1与空间分辨率的拟合公式,可为今后电晕放电数值模拟中判断电晕放电的起始时刻提供参考。     

山东大地构造相研究方法划分方案与基本特征

在系统收集山东已完成的1∶5万、1∶20万和1∶25万区域地质资料基础上,通过编制山东省1∶25万实际材料图和建造构造图、1∶50万大地构造相五要素工作底图和1∶50万大地构造相图,全面介绍了大地构造相的定义、研究内容、指导思想、基本原则与编图程序。采用大地构造相编图作为大陆动力学研究的主要方法,是揭示不同陆块之间相互作用、形成过程和演化历史、研究山东大陆块体离散、会聚、碰撞、造山的大陆动力学过程的主要载体和具体表达形式。进而对山东大地构造相进行了划分,共划出华北陆块区、秦祁昆造山系和中国东部陆缘弧盆系相系3大相系,鲁西陆块、渤海陆块、大别苏鲁结合带、威海弧盆系、胶辽岩浆弧和华北裂谷盆地6个大相以及20个相和59个亚相,明确了其鉴别标志。对陆块区、造山系和陆缘弧盆系相系以及大相、相的基本特征进行了描述;简要总结了大地构造相与成矿尤其是金矿的关系,探讨了不同矿床与大地构造相的成因联系。     

柴北缘牦牛山地区牦牛山组沉积相组合特征

柴达木盆地北缘牦牛山地区出露的牦牛山组是一套由冲积扇和扇三角洲相共同构成的陆相沉积组合,冲积扇相砾岩-粗砂岩组合主要分布于研究区SE侧,扇三角洲相砂岩-泥岩组合主要分布于研究区NW侧。古水流分析表明牦牛山组沉积物主要来自其SE侧古隆起,但后期扇三角洲相包含少量来自NW和NE向的沉积物。该套沉积组合序列特征与区域上分布在牦牛山西侧同时期形成的湖泊相、滨浅海相沉积共同表明,柴达木盆地北缘在晚志留-早泥盆世时期存在一NW向倾斜的古斜坡,且晚期北侧发生抬升。砾岩和砂岩碎屑组成与区域岩石组合类型对比表明,牦牛山组沉积碎屑物主要来自于滩间山群。沉积组合序列特征、碎屑组成和区域构造背景综合研究表明,牦牛山组可能为柴达木板块向北俯冲过程中形成的局部断陷盆地的充填物。     

短期增温和降水减少对沙质草地土壤微生物量碳氮和酶活性的影响

通过模拟气候变化,探究短期增温和降水减少对沙质草地土壤微生物量碳氮及酶活性的影响,揭示沙质草地土壤微生物量碳氮和酶活性对短期气候变化的响应规律。结果表明：（1）短期增温和降水减少对土壤微生物量碳氮和酶活性均产生显著影响。（2）在自然温度下,与自然降水相比,降水减少40%时土壤微生物量碳（MBC）和微生物氮（MBN）含量最高,增幅分别为87.9%和98.8%;降水减少60%时土壤碱性蛋白酶（S-ALPT）活性最低,降幅达32.8%。（3）在增温条件下,与自然降水相比,降水减少40%时土壤MBC和MBN含量最低,降幅分别为25.67%和48.16%,土壤脲酶（S-UE）活性最高,增幅20.42%。（4）土壤pH与3种土壤酶活性正相关,与土壤微生物量碳氮负相关。土壤微生物量碳氮与土壤纤维素酶（S-CL）活性负相关,与S-UE、S-ALPT活性正相关。     

1958—2019年云南省拐卖未成年人犯罪的时空格局及影响因素

拐卖犯罪的时间跨度长、社会危害性高,会对受害者造成一生的记忆创伤。未成年人作为弱势群体,极易受到拐卖犯罪的侵害。早前拐卖的相关研究主要集中在法学和社会学领域,基于地理学视角的研究起步较晚,且缺少针对犯罪高发区云南省的研究。为此,文章基于公益平台“宝贝回家”网站的数据资料,运用数理统计、空间分析等方法,从未成年受害群体视角探究云南省拐卖犯罪的时空格局及影响因素。研究发现：1）来自乡村的被拐未成年人占总体的77%,从乡村拐入乡村的拐卖数量最多;同时,被拐未成年人整体趋于低龄化,呈现较强的低龄男童偏好以及大龄女童偏好。2）1958—2019年云南省拐卖未成年人数量在时间上呈现“倒V型”波动特征,高发期为1994—2005年,其时间演变受特殊历史事件、国家政策和打拐活动等的影响。3）空间上,云南省东部犯罪总量较高,扩散速率较快,其中曲靖、昆明、昭通为热点区域;县域尺度上,官渡区、昭阳区、盘龙区、西山区、五华区、镇雄县、宣威市的被拐未成年人数量占总数的49.5%;同时,过半案件发生在居住场所附近,封闭式公共场所附近案件发生量最少。4）影响因素上,自然因子对拐卖犯罪的影响力度最小,人口因子对犯罪快速增长期影响显著,社会和经济因子对犯罪高发期和低发期的作用显著。