横、顺坡垄作对黑土坡面侵蚀-沉积周期规律的影响

我国东北黑土区的水土流失和土地退化正严重制约着东北地区农业经济发展,威胁国家粮食生产安全。掌握不同垄作方向耕作措施下的东北黑土区土壤侵蚀规律,对合理布设水保措施、控制水土流失等具有重要意义。采用¹³⁷Cs示踪技术并结合小波分析方法,对不同垄作方向坡耕地土壤侵蚀-沉积速率的空间变化规律开展研究。结果表明：(1)横、顺坡垄作坡面¹³⁷Cs平均浓度分别为1 802 Bq·m^-2和1 770 Bq·m^-2,均小于当地背景值2 417 Bq·m^-2,说明在两种垄作方向下均发生了不同程度的土壤侵蚀。(2)横坡垄作的坡面平均侵蚀速率(1 341 t·km^-2·a^-1)小于顺坡垄作(1 477 t·km^-2·a^-1),表明在长期平均条件下前者的水土保持作用优于后者。尽管研究区土壤侵蚀属于轻度侵蚀,但其侵蚀速率远大于黑土区的土壤容许流失量(200 t·km^-2·a^-1     

西汉水流域典型林草地侵蚀特征分析

为了说明西汉水流域典型林草地的侵蚀特征,为农业工程和流域治理提供依据,采用137Cs土壤侵蚀核素示踪技术,按野外采样、核素检测、模型计算三步开展研究。结果表明,6个本底区域的137Cs面积活度为1 600～2 402 Bq/m2,平均值为2 022 Bq/m2;本底区域和未扰动的林草地,剖面核素活度随深度呈指数递减分布;采样荒草地为轻度侵蚀,林地为沉积或无明显流失,退耕还林用地为中度侵蚀;侵蚀强度：林草地＜荒草地＜退耕还林用地;对于同坡面的不同坡位,侵蚀强度：坡面上部＞中部＞下部;植被发育程度影响侵蚀量的大小,对于同一土地利用类型,通常植被覆盖度越高,侵蚀速率越小,反之侵蚀速率越大。     

基于GIS与137Cs技术的土壤侵蚀微观研究

坡地侵蚀的研究是进行流域侵蚀研究的基础，影响坡地土壤侵蚀的因素很多，但最主要的是地形因子。通过^137Cs技术和GIS技术，以黄土高塬沟壑区的多个自然汇流坡面为研究对象，从微观角度探讨了在自然坡面条件下不同地形因子对坡面土壤侵蚀的影响，根据土壤侵蚀在坡面上的垂直分异规律．对不同部位土壤侵蚀量的差异及不同地形因子对土壤侵蚀的影响大小进行了初步探索性研究。结果表明：在微观尺度内，坡度、坡长等常规因子对土壤侵蚀的影响并不像径流小区测定的那样明显，似乎已经退居到次要位置。借助GIS对土壤侵蚀进行微观研究，可以发现一些用常规方法很难发现的规律，有助于我们更加深刻地认识土壤侵蚀的变化规律。     

粤北石漠化地区土壤侵蚀的137Cs法研究

据2005年10月的野外调查及对TM卫星影像解译分析结果,研究了粤北不同程度的石漠化地区、不同利用类型土地的¹³⁷Cs区域分布以及土壤侵蚀速率特征。结果表明:粤北石漠化地区土壤¹³⁷Cs活度的平均值为(6.54±0.57) Bq·kg^-1,土壤中¹³⁷Cs水平随石漠化程度增加有先降低然后升高的趋势,表明在重度石漠化阶段,过高的基岩裸露率导致其周围土壤对¹³⁷Cs的集中吸附,¹³⁷Cs在某些沉积小环境内逐渐富集。研究区¹³⁷Cs背景值为(1 433.60±131.40) Bq·m^-2,低于北半球的平均值,¹³⁷Cs剖面分布基本符合指数分布,最高值出现在2~4 cm深度范围内。在轻度、中度石漠化地区,非耕作土壤侵蚀速率的平均值分别为1 369.0、1 833.5 t·km^-2·a^-1;耕作土壤侵蚀速率远高于非耕作土壤,坡度对土壤侵蚀影响非常明显。     

Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco

In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the ¹³⁷Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m^− 2). All the sampling sites were eroded and ¹³⁷Cs inventories varied widely (between 245 and 3670 Bq m^− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha^− 1 yr^− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha^− 1 yr^− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha^− 1 yr^− 1 and reaching a maximum of 48.8 t ha^− 1 yr^− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha^− 1 yr^− 1) to 25° (40. 8 t ha^− 1 yr^− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha^− 1 yr^− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha^− 1 yr^− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.     

Estimation of Deposition Velocities for 85Sr, 131I, 137Cs on Spinach,Radish and Beans Leaves in a Tropical Region Under Simulated Fallout Conditions

Poly dispersive aerosols of SrCl₂, NaI, CsCl having a size distribution of 2.33 m (Activity Median Aerodynamic Diameter, [AMAD]) with a geometric standard deviation of 1.83 m are used for the determination of deposition velocity for ⁸⁵Sr, ¹³¹I and ¹³⁷Cs aerosols on tropical spinach (Spinicia olericia), radish (Raphanous sative) and beans (Phasolous valugeries) plant leaves. The experiments were carried out in a specially designed exposure chamber to simulate deposition under accidental releases of radioactivity in tropical environment. The rates of particles deposition are expressed as a function of plant surface area and of plant dry weight. The deposition velocities obtained are in the range of 10^–6 to 10^–7 m/s. These values differ significantly from those in temperate regions. The lower values for deposition velocities (v _g) for the tropical environment is attributed due to high humidity. Therefore, the deposition of suspended aerosols on leaf surfaces caused by impaction and Brownian diffusion becomes slower in tropical environment and resulted into lower value of deposition velocities.     

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     

用^137Cs法探讨苏南坡地的土壤侵蚀

与黄土和红壤地区相比 ,学术界对苏南丘陵区土壤侵蚀的关注要少得多 ,也许是这里的土壤侵蚀的绝对数量不大 ,然而 ,苏南地区的土壤侵蚀引起的生态影响却不容忽视 ,如因土壤侵蚀造成的养分流失对水体的影响及土层减薄都远超过黄土区。为了探讨苏南土壤侵蚀的生态影响 ,首先是要了解土壤侵蚀的状况 ,在这方面 13 7Cs示踪法是一种非常有用的工具 ,可是要使用此法 ,必须要解决两个问题 ,一是确定研究区的背景值 ,二是建立估算土壤侵蚀的模型。经过较长时间的研究 ,确定苏南地区的 13 7Cs背景值为 2 2 0 0 Bq/m2 ;并根据基本物理含义 ,建立了耕地与非耕地的土壤侵蚀模型 ,用这 2个模型并借用其他学者提供的土壤沉积模型 ,对宜兴竹园及茶园两个坡地的土壤侵蚀与沉积作了估算。在此基础上 ,又尝试着简单探讨了土壤侵蚀引起的土层及养分流失的生态影响     

A preliminary assessment of the potential for using Pbex measurement to estimate soil redistribution rates on cultivated slopes in the Sichuan Hilly Basin of China

In order to assess its potential for estimating soil redistribution rates, the naturally occurring fallout radionuclide ²¹⁰Pb_ex has been used in parallel with ¹³⁷Cs, derived from the atmospheric testing of nuclear weapon testing in the 1950s to 1970s, to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Jiajia Village, Jianyang County, in the Sichuan Hilly Basin of China. The local ²¹⁰Pb_ex reference inventory of 12,860 Bq m^− 2 is higher than those reported for many other areas of the world and may reflect the influence of cloudy weather in preventing ²¹⁰Pb released to the atmosphere across the local region moving up into the upper troposphere, where is would be more widely dispersed. The mean ²¹⁰Pb_ex and ¹³⁷Cs inventories measured in cores collected from the upper part of the field with an average slope of 10° were 8028 Bq m^− 2 and 993 Bq m^− 2, respectively, and the equivalent values for the lower part of the field, where the slopes are steeper (20°) were 11,388 Bq m^− 2 and 1299 Bq m^− 2. The pattern of post-fallout ²¹⁰Pb_ex and ¹³⁷Cs redistribution on the sloping field reflects not only the effects of water erosion and redistribution by tillage, but also the local traditional practice of “Tiaoshamiantu”, whereby sediment trapped in the ditches is returned to the fields by the farmer. The estimates of annual rates of soil loss provided by the ²¹⁰Pb_ex measurement are closely comparable with those derived from the ¹³⁷Cs measurements and are consistent with existing knowledge for the study area. The results obtained from this study confirm the potential for using ²¹⁰Pb_ex measurement to estimate soil erosion rates over medium-term timescale of 50–100 years. By combining the estimates of erosion rates provided by the ²¹⁰Pb_ex and ¹³⁷Cs measurements, the weighted mean net soil loss was estimated to be 48.7 t ha^− 1 year^− 1 from the upper subfield and 16.9 t ha^− 1 year^− 1 from the lower subfield. These rates are considerably lower than the erosion rates obtained from runoff plot measurements in the local area. It is suggested that the traditional erosion control practices and the practice of “Tiaoshamiantu” have a significant effect in reducing soil loss and conserving valuable cultivated soil on sloping fields in the Sichuan Hilly Basin.     

岩溶区坡面土壤侵蚀特征研究

以重庆南川岩溶区为例,用137C s法研究了岩溶区坡面土壤侵蚀特征。结果表明,坡面上部侵蚀速率较小,平均侵蚀速率为400.8 t/(km2.a),最大侵蚀速率为1 138.4 t/(km2.a);坡面中部侵蚀加剧,平均侵蚀速率2 264.8 t/(km2.a),最大侵蚀速率可达3 760 t/(km2.a);坡面下部侵蚀减弱甚至堆积。土壤表层有机质、表层粘粒及水稳性团聚体含量在坡面上的变化与土壤侵蚀速率具有负相关趋势。