辽东湾沿岸土壤中~(137)Cs背景值及分布特征研究

在辽东湾沿岸区域采集了20个土壤表层样和7个非耕作土壤剖面样(其中一个为标准剖面),通过对采集的土壤样品中的137 Cs进行测量与分析,确定该区域土壤中137 Cs的背景值,并探讨了土壤中137 Cs的分布特征。结果表明,研究区137 Cs的背景值为(1 704±40)Bq/m2;表层土壤中137 Cs的比活度范围为0.84～19.90Bq/kg,不同土地利用类型表层土壤中的137 Cs比活度有明显差异,比活度高低依次为:草地>盐碱地>耕地;非耕作土壤剖面中137 Cs的总量范围为65～1 535Bq/m2,大部分土壤剖面中137 Cs呈指数递减分布,且剖面中的137 Cs发生不同程度的流失,而受到沉积扰动作用的剖面中137 Cs分布无规律。通过探讨辽东湾沿岸区域土壤中137 Cs的背景值及137 Cs的分布特征,为利用137 Cs示踪技术定量研究该区域物质输移和辽东湾沉积物来源提供依据。     

强度耕作对137Cs、210Pbex和有机质剖面分布的影响

很少有关于直接测定强度耕作侵蚀引起土壤退化过程的报道.我们的目的是确定应用137Cs和210Pbex直接定量评价耕作侵蚀对土壤有机质(SOM)坡面运移影响的可能性.我们在黄土高原陡坡耕地上进行了50次犁耕活动,并将与其相临的另一块陡坡耕地作为对照.在对照坡地不同坡位,137Cs浓度均匀分布于上部0～30 cm土层,而210Pbex浓度在坡上部和坡中部随土层深度增加呈现线性递减,在坡下部呈指数函数递减.0～30 cm土层中土壤有机质含量显著大于30 cm深度以下土层,并在坡中部和坡下部呈现与210Pbex类似的土壤剖面分布特征.与对照坡地比较,50次犁耕活动导致坡上部、坡中部0～45 cm土层的SOM含量分别降低了38%和47%,坡下部0～100 cm土层中的SOM含量却提高了18%.坡上部土壤剖面中137Cs浓度的加权平均值从1.48 Bq/kg降低到0.29 Bq/kg, 坡中部从2.53 Bq/kg减少到0.33 Bq/kg,坡下部从1.48 Bq/kg提高到2.81 Bq/kg.210Pbex浓度的剖面加权平均值在坡上部从27.71 Bq/kg下降到6.15 Bq/kg,在坡中部和坡下部分别从35.46 Bq/kg和25.53 Bq/kg降低到1.57 Bq/kg和19.40 Bq/kg.137Cs和210Pbex的剖面分布与SOM在p<0.001水平呈显著相关,相关系数R2值在对照坡地为0.81～0.86,在犁耕实验坡地为0.86～0.91.实验结果表明,环境放射性核素137Cs和 210Pbex在黄土高原陡坡地遵照同一物理运移机理,可直接应用于定量评价耕作侵蚀与土壤质量的关系.     

紫色土草地表层土壤137Cs含量与粒度和有机质的相关性研究

紫色土草地表层土壤的137Cs比活度与样品的筛分中值粒径(d50)相关较好,而与颗分中值粒径没有明显的相关性。137Cs主要被吸附于土壤颗粒的表面,土壤团聚体表面的矿物、岩石碎屑颗粒的137Cs吸附浓度高于团聚体内部的碎屑颗粒。筛分粒度中等的样品有机质含量高,粗和细粒度的样品有机质含量均低,137Cs比活度和有机质含量无明显相关。     

基于137Cs示踪的丹江口市农用地土壤侵蚀与有机质流失分析

运用137Cs示踪技术探讨了丹江口市小流域不同土地利用方式的土壤侵蚀,并分析了137Cs含量与有机质和重金属含量之间的关系。结果表明:农用地土壤侵蚀速率从大到小依次为沟谷旱地>坡耕地>菜田>水田>草地>灌丛,耕作土的侵蚀强度多为中度和强度侵蚀,非耕作土则是微度和轻度侵蚀;不同土地利用方式对土壤有机质和重金属分布影响很大,有机质含量分布规律为草地>灌丛>菜田>水田>沟谷旱地>坡耕地;Pb与Ni含量为灌丛>草地>坡耕地>沟谷旱地>菜田>水田;Cr与Cu含量为灌丛>菜田>坡耕地>草地>沟谷旱地>水田;Zn含量为灌丛>菜田>草地>坡耕地>沟谷旱地>水田。对137Cs含量与土壤有机质、重金属含量进行回归分析的相关系数均在0.7以上,说明在景观简单的小流域,可以利用137Cs含量和数学模型预测土壤有机质和重金属的含量变化。     

宁南黄土高原土壤137Cs分布与相关影响因子研究

利用137Cs示踪方法,对宁南黄土高原阳洼流域纵断面土壤137Cs分布及相关影响因子进行了初步研究。结果表明:流域纵断面137Cs面积活度随坡面海拔和水平距离的变化,表现为一种不规则的波动振荡趋势。随海拔降低,纵断面上、中部137Cs面积活度逐步下降,有明显的土壤侵蚀发生;坡面下部137Cs面积活度最高,泥沙沉积的再分布现象明显。流域内林草地剖面土壤137Cs呈指数型分布,坡耕地、梯田137Cs在耕层内呈均一分布,其分布模式与各土地类型土壤有机质的分布状态完全一致。相关分析表明,两者在P<0.01水平达到极显著相关(r2=0.336,n=417)。土壤137Cs的损失和土壤有机质的移动具有相同的物理路径和运移机制;农耕坡地土壤137Cs面积活度随坡度增加有逐步降低的趋势;土地利用方式、坡度、耕作活动是影响纵断面土壤137Cs空间异质性的主要因素。137Cs示踪方法是研究土壤侵蚀空间分布的一种有效工具。     

强度耕作对^137Cs、^210Pbex和有机质剖面分布的影响

很少有关于直接测定强度耕作侵蚀引起土壤退化过程的报道。我们的目的是确定应用137Cs和210Pbex直接定量评价耕作侵蚀对土壤有机质(SOM)坡面运移影响的可能性。我们在黄土高原陡坡耕地上进行了50次犁耕活动,并将与其相临的另一块陡坡耕地作为对照。在对照坡地不同坡位,137Cs浓度均匀分布于上部0～30cm土层,而210Pbex浓度在坡上部和坡中部随土层深度增加呈现线性递减,在坡下部呈指数函数递减。0～30cm土层中土壤有机质含量显著大于30cm深度以下土层,并在坡中部和坡下部呈现与210Pbex类似的土壤剖面分布特征。与对照坡地比较,50次犁耕活动导致坡上部、坡中部0～45cm土层的SOM含量分别降低了38%和47%,坡下部0～100cm土层中的SOM含量却提高了18%。坡上部土壤剖面中137Cs浓度的加权平均值从1.48Bq/kg降低到0.29Bq/kg,坡中部从2.53Bq/kg减少到0.33Bq/kg,坡下部从1.48Bq/kg提高到2.81Bq/kg。210Pbex浓度的剖面加权平均值在坡上部从27.71Bq/kg下降到6.15Bq/kg,在坡中部和坡下部分别从35.46Bq/kg和25.53Bq/kg降低到1.57Bq/kg和19.40Bq/kg。137Cs和210Pbex的剖面分布与SOM在p<0.001水平呈显著相关,相关系数R2值在对照坡地为0.81～0.86,在犁耕实验坡地为0.86～0.91。实验结果表明,环境放射性核素137Cs和210Pbex在黄     

基于137Cs的土壤沉积速率的定量模型

在假设137Cs在耕层中得到充分混合而变得均一的基础上,根据质量平衡原理建立了一个根据农业耕作土壤剖面中137Cs的沉积量和土壤沉积量之间关系的定量模型.在建立模型的过程中,充分考虑了137Cs的衰变常数,年沉降分量,耕层厚度和采样年份等因素.模型的模拟结果表明,137Cs的沉积量与年平均土壤沉积量之间的关系是一种复杂的曲线关系.     

宁南黄土高原土壤^137Cs分布与相关影响因子研究

利用^137Cs示踪方法,对宁南黄土高原阳洼流域纵断面土壤^137Cs分布及相关影响因子进行了初步研究。结果表明：流域纵断面^137Cs面积活度随坡面海拔和水平距离的变化,表现为一种不规则的波动振荡趋势。随海拔降低,纵断面上、中部^137Cs面积活度逐步下降,有明显的土壤侵蚀发生;坡面下部^137Cs面积活度最高,泥沙沉积的再分布现象明显。流域内林草地剖面土壤^137Cs呈指数型分布,坡耕地、梯田^137Cs在耕层内呈均一分布,其分布模式与各土地类型土壤有机质的分布状态完全一致。相关分析表明,两者在P〈0．01水平达到极显著相关（r^2=0．336,n=417）。土壤^137Css的损失和土壤有机质的移动具有相同的物理路径和运移机制;农耕坡地土壤^137Cs面积活度随坡度增加有逐步降低的趋势;土地利用方式、坡度、耕作活动是影响纵断面土壤^137Cs空间异质性的主要因素。^137Cs示踪方法是研究土壤侵蚀空间分布的一种有效工具。     

基于土壤~(137)Cs监测的土壤侵蚀与有机质流失——以密云水库为例

本文运用137Cs核素示踪技术,研究北京重要的水源供应地密云水库周边地区及白河上游地区土壤侵蚀状况与有机质流失状况及其相互之间的量变关系。试验结果表明:0～20cm土层中山坡上137Cs含量低于坡中、坡下,但若山顶具有缓坡或山角下具有陡坡则137Cs含量变化规律相反。根据水利部标准与土壤137Cs监测结果,密云水库周边大部分地区基本属于轻度侵蚀和中度侵蚀,部分地区侵蚀情况严重,达到了剧烈侵蚀的程度。不同土地利用方式对土壤有机质分布有很大影响,有机质含量分布为灌丛>林地>果园>农田;上游地区有机质含量高于水库周边地区土壤,表明人为活动加剧了土壤侵蚀和有机质的流失。对于景观单一,地域较小的采样区进行三次曲线数学模拟,其相关系数高达0.9左右,表明在监测土壤137Cs、210Pb含量变化的同时,可以利用小区域数学模型直接预报预测土壤有机质含量的变化。     

赣南红壤丘陵区137Cs示踪土壤侵蚀对土壤养分元素的影响

赣南红壤丘陵区是我国土壤侵蚀与土地退化比较严重的地区,以南丰县为例,应用137 Cs示踪技术探讨不同土地利用方式下土壤侵蚀与养分元素的关系。结果表明:(1)湿地松林、桔园、水田3种土地利用方式作用下土壤中137 Cs与养分元素分布差异显著,在垂直剖面上,湿地松林137 Cs含量呈指数递减分布,水田与桔园137 Cs含量因人为干扰在耕层内均匀分布;有机质与137 Cs有相似的分布特征;全氮、碱解氮、速效磷、速效钾含量均呈现一定表聚性。(2)位于坡地的2种土地利用方式中,湿地松林137 Cs、全氮、碱解氮、速效磷、速效钾、有机质含量均表现为下坡>上坡>中坡;桔园137 Cs活度表现为中坡>下坡>上坡,全氮、碱解氮、速效磷表现为下坡>中坡>上坡,而速效钾、有机质最大值均出现在上坡。(3)相关性分析表明,土壤137 Cs与有机质、全氮、碱解氮显著正相关,表明小流域有机质、氮元素可能与137 Cs有相同的物理运移方式,pH与137 Cs显著负相关,速效磷、速效钾则与137 Cs不相关。(4)3种土地利用方式中位于小流域谷地的水田137 Cs、有机质、全氮、碱解氮含量最高,坡地上桔园坡面137 Cs与土壤养分元素含量均高于湿地松林地,表明一定程度的坡改梯桔园种植模式能有效缓解土壤侵蚀与养分流失,改善区域生态环境。     

The extent and significance of bioturbation on 137Cs distributions in upland soils

Differences between measured ¹³⁷Cs activity–depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed ¹³⁷Cs in mineral and organic upland soils in southern Scotland. Bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age (non-native tree pollen and spheroidal carbonaceous particles, SCPs). The causes and mechanisms of bioturbation were further investigated by soil micromorphology. Well-drained mineral soils with active populations of earthworms are the most bioturbated, showing near-complete homogenisation to depths of about 20 cm. Enchytraeids also seem to remobilise ¹³⁷Cs by the digestion of organic matter and may be the main cause of ¹³⁷Cs redistribution in organic-rich upland soils. Relative rates of mixing are evaluated by comparing ¹³⁷Cs depth profiles.     

利用137Cs估算土壤侵蚀速率的定量模型

A quantitative model was developed to relate the amount of ^137Cs loss from the soil profile to the rate of soil erosion,According th mass balance model,the depth distribution pattern of ^137Cs in the soil profile ,the radioactive decay of ^137Cs,sampling year and the difference of ^137Cs fallout amount among years were taken into consideration.By introducing typical depth distribution functions of ^137Cs into the model ,detailed equations for the model were got for different soil,The model shows that the rate of soil erosion is mainly controlled by the depth distrbution pattern of ^137Cs ,the year of sampling,and the percentage reduction in total ^137Cs,The relationship between the rate of soil loss and ^137Cs depletion i neither linear nor logarithmic,The depth distribution pattern of ^137Cs is a major factor for estimating the rate of soil loss,Soil erosion rate is directly related with the fraction of ^137Cs content near the soil surface. The influences of the radioactive decay of ^137Cs,sampling year and ^137Cs input fraction are not large compared with others.     

Vertical distribution and bioavailability of 137Cs in organic and mineral soils

The vertical distribution and bioavailability of ¹³⁷Cs in Histosols and mineral soils with different physicochemical properties from the southeast of Bavaria (Germany) more than ten years after the Chernobyl accident were the focus of this study. The vertical distribution of ¹³⁷Cs was low in the investigated soils. About 85–98 % of the total ¹³⁷Cs was located in the upper 10 cm of the mineral soils. Slightly higher ¹³⁷Cs percentages were observed in deeper soil layers of the peat soils. Although the organic matter is assumed to enhance ¹³⁷Cs mobility in soils, ¹³⁷Cs was also located in the upper 10 cm of the peat soils (73–85 %). The highest ¹³⁷Cs‐activities were found in the humus layers of forest soils, where 45–93 % of the total ¹³⁷Cs soil inventories were observed. To determine the bioavailability of radiocesium, the soil‐to‐plant transfer of ¹³⁷Cs and additionally added ¹³⁴Cs was investigated under controlled conditions. The results revealed that the ^134+137Cs soil‐to‐plant transfer factors as well as the percentages of NH₄‐exchangeable ^134+137Cs were much higher for the peat soils and humus layers than for the mineral soils. Nevertheless, the migration of ¹³⁷Cs from the humus layers to the underlying soils was low. Considering the high bioavailability and low migration of radiocesium in the humus layers, it is suggested that radiocesium is involved in a shortcut element cycle in the system humus layer‐plant uptake‐litter. Furthermore, the organic matter has to be taken into account for radiocesium immobilization.     

Distribution of 137Cs and 60Co in plough layer of farmland: Evidenced from a lysimeter experiment using undisturbed soil columns

Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant(NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment(800 d), >96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils;very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth(25 cm) in both soils. Three phases on the vertical migration rate(v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement(0–355 d, v = 219 ± 17 mm year-1), followed by a steady movement(355–577 d, v = 150 ± 24 mm year-1) and a very slow movement(577–800 d, v = 107 ± 7 mm year-1). In contrast, its migration rate in the brown soil(v = 133 ± 17 mm year-1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon(SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer(0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface(20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades.Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.     

利用137Cs示踪农业耕作土壤侵蚀速率的定量模型

建立了一个根据农业耕作土壤剖面中^137Cs的损失量与土壤侵蚀量之间关系的定量模型,在假设^137Cs在耕层中得到充分的混合而变得均一的基础上,根据质量平衡模型推导而成,模型显示^137Cs的衰变常数,年沉降分量,耕层厚和采样年份对年平均土壤侵蚀速率都有重大影响,模型结果还说明,^137Cs的损失量与年平均土壤侵蚀量之间的关系既非线性关系亦非指数关系,而是一种复杂的曲线关系。     

农耕地土壤137Cs与210Pbex深度分布过程对比研究

探讨了137Cs与210Pb_ex在农耕地土壤深度分布过程的差异。基于137Cs与210Pb_ex的不同沉降过程,考虑到核素由犁耕层向犁底层的扩散,对农耕地土壤137Cs、210Pb_ex的深度分布过程进行了理论推导,并以杨凌符家庄麦田剖面的实测数据予以验证,同时讨论了实测符家庄麦田剖面137Cs、210Pb_ex深度分布的规律特征及其原因,以此阐明了137Cs与210Pb_ex在农耕地土壤深度分布过程的差异。137Cs源于大气核试爆,没有持续沉降补充,犁耕层和犁底层土壤137Cs深度分布一直处于随时间变化的非稳定态;而210Pb_ex是天然核素,存在大气沉降的持续补充,犁耕层和犁底层土壤210Pb_ex深度分布最终呈稳定态。农耕地土壤137Cs、210Pb_ex深度分布的实测值曲线与理论值曲线的差异,尤其210Pb_ex,可能与耕作深度的变化历史或土地利用(覆被)变化有关。