75 resultados para 210Pb ex, 7Be, 137Cs, Soil, Areal Activity Density

em Chinese Academy of Sciences Institutional Repositories Grid Portal


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滇西和黔中28个表土剖面分层土样7Be、137Cs比活度对比分析可见:滇西地区表土层顶部7Be/137Cs为100~1000,而黔中地区仅10~100;两地区表土层中7Be的表观比活度和最大渗透深度总体相近;137Cs在黔中表土层中的比活度总体较滇西地区略高。而黔中表土中7Be累计值的偏低现象,映射了该地区强烈的水土流失。为解释滇西和黔中地区之间表土层顶部7Be/137Cs的地区差异,需进一步讨论两核素的湖泊沉积物蓄积特征。

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沉积物柱芯分别采自滇西地区的洱海和黔中地区的红枫(及百花)湖,散落核素^7Be和^137Cs在沉积物中的蓄积特征对比分析表明,^7Be在洱海及红枫湖沉积物中的累计值分别为(237±73)Bq/m^2和(783±44)Bq/m^2;按校正到沉降年代的数值,1986年以前^137Cs的累计值分别为(519±26)Bq/m^2及(3704±56)Bq/m^2。由模式计算获知,(1)^7Be和^137Cs在红枫湖沉积物中的蓄积以侵蚀影响为主;在洱海的蓄积受直接散落控制。(2)在洱海和红枫湖地区^7Be大气散落累计值分别为(0.07±0.02)Bq/cm^2及(0.08±0.01)Bq/cm^2;1986年以前^137Cs大气散落累计值分别为(0.11±0.01)Bq/cm^2及(0.37±0.01)Bq/cm^2,显示出滇西与黔中地区之间^137Cs散落的地区差异。这一现象可能反映出青藏高原对滇西地区存在着全球性大气扩散污染物散落的屏蔽效应。

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The relationships of eight moss species of Dicranum in 31 sites in main ecological systems in the Changbai Mountain with environmental factors were studied by canonical correspondence analysis (CCA). The results showed that altitude, soil sand percentage, water percentage, acidity and canopy density were important environmental factors influencing the distribution of the species of Dicranum . The relationships between Dicranum elongatum Schleich. ex Schwaegr ., D.groenlandicum Brid. and altitude,between D.japonicum Mitt., D.scoparium Hedw. and canopy density,between D.polysetum Sw., D. undulatum Schrad. ex Brid. and soil acidity and water percentage,were positively correlative. The niche overlaps among the eight species of Dicranum were calculated. The minimal spanning tree of the eight species on the two-dimensional scatter plot were also drawn based on their niche overlaps, which clearly revealed the ecological similarities of eight species.

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A probabilistic soil moisture dynamic model is used to estimate the soil moisture probability distribution and plant water stress of irrigated cropland in the North China Plain. Soil moisture and meteorological data during the period of 1998 to 2003 were obtained from an irrigated cropland ecosystem with winter wheat and maize in the North China Plain to test the probabilistic soil moisture dynamic model. Results showed that the model was able to capture the soil moisture dynamics and estimate long-term water balance reasonably well when little soil water deficit existed. The prediction of mean plant water stress during winter wheat and maize growing season quantified the suitability of the wheat-maize rotation to the soil and climate environmental conditions in North China Plain under the impact of irrigation. Under the impact of precipitation fluctuations, there is no significant bimodality of the average soil moisture probability density function.

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Terrestrial carbon pool mainly consists of three parts: the active carbon pool of the vegetation,soil carbon pools and the lithosphere carbon pool of less activity. Under natural conditions,vegetation carbon pools,soil carbon exchange with atmospheric carbon pool directly,the lithosphere participate in the global carbon cycle by weathering Our research have coverd the soil organic carbon density,plant biomass (carbon density),plant net primary productivity of past 40 ka,and the magnetic susceptibility,grain size,weathering of silicate carbon consumption of past 140 ka. This study has achieved a number of conclusions as shown below. 1 Silicate weathering CO2 consumption in the long-term fluctuations with a similar deep-sea δ18O record,demonstate that it not only can be used as one of the instructions of terrestrial carbon pool,even can be used as indicators of global environmental change; silicate weathering CO2 consumption and susceptibility shown a clear relationship between lag or lead at different times,it maybe lies on how the climate change. 2 Soil carbon pools in line with the global climate on long-term,but the relationship between soil carbon density and climate change was not obvious in short-term change,generally lags behind the changes in other climatic proxies. 3 Carbon density of vegetation and other proxy indicators of climate have good consistency. In the study period,perform the cycle of glacial and interglacial completely,but because of the ancient vegetation of accurate information is difficult to obtain,it did not reflect rapid response to climate change. 4 Cooling events is conducive to soil organic carbon accumulation but not conducive to weathering and vegetation growth. High temperature environment is not conducive to the accumulation of soil organic carbon. 5 In the deglacial time from the last glacial maximum to the Holocene,weathering carbon consumption seems earlier than vegetation and soil organic carbon in the fluctuant increase.Does it imply that the effects of silicate weathering is an important factor to the global carbon cycle and global climate change? It is worth further research.

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云贵高原是青藏隆起在南亚大陆形成的一个海拔梯度大、地势格局复杂的特异环境单元。该地域兼受东南季风与西南季风的交汇影响,是全球变化的敏感区之一。青藏隆起对云贵高原现代环境影响主要表现在:1)全球性大气扩散污染物的屏蔽效应和局地性大气扩散污染物的滞留效应;2)区域化学风化的增强效应和物理侵蚀的梯级效应;3)地表环境地球化学过程的低纬度-高海拔效应。核素示踪模式分析表明:滇西与黔中地区之间^137Cs自大气散落差异明显[1986年以前,洱海和红枫湖沉积物中^137Cs散落的累计值分别为(0.11±0.01)Bq/cm^2及(0.37±0.01)Bq/cm^2],而^7Be的散落相近。这说明青藏隆起对滇西地区存在全球性扩散大气污染物散落的屏敝效应。

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为了确定合理环保的耕作制度,2007~2008安塞田间定位试验黄土丘陵旱作农区大豆(Glycine maxL)、玉米(Zea maysL)、红小豆(Semen Phaseoli)、马铃薯(Solanum tuberosumLinn.)在翻耕化肥(CF)、翻耕有机肥(CM)、翻耕无肥(CN)、免耕化肥(NF)、免耕有机肥(NM)、免耕无肥(NN)等水平下的农田土壤脲酶、蔗糖酶活性。结果表明:在作物花期,大豆、玉米土壤脲酶活性较高,蔗糖酶活性较低,而红小豆、马铃薯则与之相反,差异极显著。到作物收获后,玉米土壤脲酶、蔗糖酶活性增高,增幅在83%以上,而马铃薯、红小豆、大豆三种作物土壤脲酶活性降低,降幅在10%以上,蔗糖酶活性增强,增幅在40%以上。从花期到收获后,免耕降低了土壤脲酶活性,提高了土壤蔗糖酶活性,在黄土丘陵沟壑旱作农区两种土壤酶活性表现较优的作物为大豆、玉米,较优的处理为NM玉米、NF大豆,其田间环保效应为:作物生长期间两种酶活性比较高,收获后两种酶活性则降低,有利于提高作物生长期土壤肥效利用率,减少作物收获后温室气体的排放。

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对黄土丘陵沟壑地区不同土地利用模式土壤酶活性和土壤微生物进行了测定,研究了土壤酶活性、微生物与土壤主要肥力指标对黄土丘陵沟壑地区不同土地利用模式下土壤肥力质量的关系。结果表明,不同土地利用模式0~20 cm土壤酶活性之间差异明显,而20~40 cm不同土地利用模式之间土壤酶活性差异较小,研究区域不同土地利用模式土壤微生物数量差距较大。本研究利用因子分析法来分析不同土地利用方式土壤酶活性、土壤微生物数量和土壤主要肥力指标,并根据各因子之间综合得分得出:日光温室的土壤肥力效益最好,然后依次为农田、拱棚、经济作物、果园。

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试验研究了在延安日光温室不同前茬作物条件下,黄瓜随着生长季节的变化其产量和品质及土壤呼吸和酶活性的动态变化。结果表明,前茬为豇豆的黄瓜产量和土壤碱性磷酸酶活性较高,前茬为番茄的黄瓜可溶性糖含量和土壤呼吸强度较高,前茬为四季豆的黄瓜维生素C含量较高,前茬为翻青玉米的黄瓜硝酸盐含量和土壤脲酶活性较高,前茬为翻青黑豆的土壤蔗糖酶活性较高。从提高黄瓜产量的角度出发,豇豆-黄瓜是最佳模式,而从改善黄瓜品质的角度出发,番茄-黄瓜和四季豆-黄瓜是最优模式

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对半干旱区黄土高原草地在封育和放牧条件下土壤种子库种子密度、种子库组成、种子库物种多样性及均匀性进行了比较研究,并得出主要结论:1)封育提高土壤种子库的植物种类和密度,使优良禾草和多年生植物增加。2)种子库的垂直分布规律是随着土层的加深,种子在数量上递减的速度较快。3)坡向和坡位对土壤种子库有较大影响,种子库密度变化趋势是阴坡>阳坡;坡下部>坡中部>坡上部。4)从丰富度、Shannon-Wiener多样性和均匀性3个方面比较分析封育和放牧样地土壤种子库多样性,得出封育样地Margalef丰富度指数和Shannon-Wiener指数都高于放牧地,Pielou均匀性指数低于放牧地。

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东北黑土是我国重要的商品粮生产基地,在保证我国的粮食安全中起着重要作用。鉴于东北黑土所具有的重要战略地位及其面临的严峻形势,如何通过化肥合理配施培肥黑土已经成为一个亟待解决的关键问题。 本文以东北黑土为供试土壤,设置CK、C、N、P、NP、CN、CP、CNP,8个养分组合,进行室内恒温模拟培养。通过对黑土呼吸强度的监测,研究黑土微生物活力对不同养分响应的规律;同时采用磷脂脂肪酸(Phospholipid Fatty Acids, PLFAs)和中性脂肪酸(Neutral Lipid Fatty Acids, NLFAs)为标识物,研究黑土微生物群落结构以及生理生态特性在不同养分条件下的动态变化,揭示黑土微生物活力与群落组成对不同养分响应的规律。 研究结果表明:黑土微生物活力首先受到可利用C源的限制,单加葡萄糖能够使土壤呼吸释放的CO2-C累积量达到对照的10倍以上,使黑土微生物活力显著提高;而在碳限制的状况被缓解后,氮便成为黑土微生物生长的主要限制因素,可利用碳底物充足的条件下,N的加入能够显著提高土壤呼吸强度,使释放出的CO2-C累积量达到对照处理的13倍以上,CN交互作用非常显著;在碳氮养分都充足的条件下,P的施入能更好地刺激微生物生长,提高黑土微生物活力,CNP处理,黑土微生物活力在培养的第3 d即达到峰值。CN和CNP组合能够迅速刺激真菌、细菌生长,使PLFA和NLFA含量、真菌/细菌比值均增加;并且CNP组合优于CN组合。单独加入C和CP组合,不能在短时间内使真菌、细菌的PLFA和NLFA含量显著增加,真菌/细菌比值也处于较低的水平。G+/G-比值在CN条件下,达到最大之后逐渐趋于平稳;而在单加C、CP和CNP条件下,G+/G-比值均在培养时间内达到两次峰值,显示出不同的养分条件下,微生物群落结构发生着内在的动态变化。

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土壤微生物参与陆地生态系统物质循环和能量流动,在土壤生态过程中起着重要作用。在森林生态系统管理过程中,森林树种组成的变化能影响土壤微生物数量和活性,这种影响的一个主要途径是通过森林凋落物的改变。我国南方杉木人工林取代地带性天然次生阔叶林后,林地土壤质量退化,随着杉木人工纯林的连栽,土壤质量进一步退化。树种单一化可能是引起土壤质量退化的一个重要原因,然而目前对其机理的认识十分有限。因此,本文比较研究了不同杉木人工林分布区(南带、中心产区、北带)杉木人工林和天然次生阔叶林土壤有机碳等土壤化学性状、土壤微生物数量以及土壤微生物活性特征。并且对位于中心产区的杉木人工林和天然次生常绿阔叶林土壤速效N、P、K养分及土壤酶活性的动态特征进行了研究,样地设在中国科学院会同森林生态实验站实验林场。同时,通过田间模拟试验,深入研究了不同杉阔叶凋落物(50%杉木+5O%恺木、50%杉木+500k枫香、330&杉木+33%恺木+33%枫香)以及单一杉木叶凋落物对土壤化学性状、土壤微生物生物量碳(MBC)、土壤微生物活性等指标的影响。研究结果表明:(1)广西柳州、湖南会同、河南信阳三个地区杉木人工林与天然次生阔叶林相比,林地表层土壤总有机碳量下降分别达58.24%、36.55%、31.51%,土壤全N、全P含量亦有不同程度下降,林地表层土壤C/N、C/P比也呈降低趋势;三个地区的杉木人工林与天然次生林相比,土壤细菌数量分别降低了59.03%、88.25%、76.85%,真菌数量分别下降72.17%、43.15%、28.33%;杉木人工林土壤脉酶、蔗糖酶、脱氢酶、过氧化氢酶、土壤呼吸强度均低于天然次生林土壤,而土壤多酚氧化酶活性反而增加。(2)各季节天然次生阔叶林土壤氨态氮、硝态氮、有效P、有效K含量均高于杉木人工林;杉木人工林土壤酶活性具有明显季节动态特征,而天然次生阔叶林土壤酶活性季节性变化较小,但是天然次生阔叶林土壤酶活性普遍高于杉木人工林土壤酶活性。(3)凋落物模拟试验结果表明混合凋落物能在一定程度上改善土壤微生物生物量碳、代谢嫡(成0a)、微生物嫡(Cmic/C01^9)、土壤脉酶、蔗糖酶、脱氢酶、多酚氧化酶活性等土壤质量的微生物学指标,尤其是杉木恺木这一组混合凋落物对土壤质量的改善似乎更有效。2004年4月份取样分析结果,SQF、SQ、SF处理土壤微生物生物量碳是咫处理土壤微生物生物量碳的1.64倍、1.64倍、1.28倍,10月份取样分析结果,SQF、SQ、SF处理土壤微生物生物量碳是PS处理的1.25倍、1.37倍、1.46倍;土壤代谢熵(qCO2)值在不同处理间表现出明显的差异(P<0.05),两次取样比较结果均是PS处理qCO2值最高,其次为SF、SQF,最小为SQ;然而,不同处理凋落物对土壤总有机碳(TOC)等土壤化学性状影响差异不大。杉木人工林取代天然次生阔叶林后,由于森林生态系统生物多样性减少,林地凋落物质量变差,这可能是导致杉木人工林土壤质量退化的一个重要原因。增加人工林生态系统植物多样性,通过营造混交林(然而需要考虑混交树种的选择),改善林地凋落物质量,这一林地经营管理模式能在一定程度上减缓森林土壤质量退化。