多核素联合示踪技术在土壤侵蚀研究中的应用进展

应用多核素联合示踪技术研究土壤侵蚀已成为水土保持、土壤等学科的国际前沿研究热点之一。在介绍核素137Cs、210Pb、7Be示踪土壤侵蚀原理的基础上,重点阐述了多核素联合示踪技术和稀土元素(REE)示踪技术在土壤侵蚀研究中的应用,并对今后的应用研究方向进行了分析与展望。     

近十年来核素示踪技术在土壤侵蚀研究中的应用进展

随着核素示踪技术在土壤侵蚀研究中应用的深入,土壤侵蚀研究进入了一个快速发展阶段。本文阐述了近十年来137Cs2、10Pbex7、Be、复合示踪及REE-INAA示踪等几种主要核素示踪技术在土壤侵蚀速率、泥沙沉积速率、泥沙来源和坡面侵蚀过程等研究中的应用新进展,并对今后的研究方向和发展趋势进行了分析。     

核素示踪技术在土壤侵蚀研究中的应用进展

介绍了单核素 (137Cs、2 10 Pb和7Be)、复合核素 (7Be、2 10 Pb、2 2 6 Ra和137Cs)及稳定性稀土元素 (REE)示踪技术在土壤侵蚀速率、泥沙沉积速率、侵蚀产沙时空分布和侵蚀类型转变等研究中的应用现状 ,并对各方法做了简要评价。     

核素示踪在土壤侵蚀研究中的应用

利用示踪技术研究土壤侵蚀在国外已有30多年的历史,因其具有分析精度和量化程度高,能对土壤侵蚀时空变化进行定量监测的优势而受到重视。分别介绍了单核素示踪（¹³⁷Cs）,多核素复合示踪（⁷Be, ²¹⁰Pb, ²²⁶Ra, ²³⁰Th, ¹³⁷Cs）在土壤侵蚀和泥沙来源研究领域中的进展情况,并详细阐述利用稳定性稀土元素（REE）示踪在研究泥沙来源,侵蚀产沙时空分布方面也是一种有效的方法,最后对各种方法做了简要评价。     

赤水市水土保持生态修复工程生态效益评价研究

以赤水市水土保持生态修复工程为依托,对水土保持生态修复效益评价方法进行了探索,建立了开展水土保持生态修复工程生态效益调查、评价的基本技术与方法。评价中坚持了客观性和系统性原则,以植被覆盖度,生物多样性,群落生物量,土壤有机质,N,P,K含量,表土侵蚀和泥沙含量变化为评价指标,通过野外定位监测获取水土流失、植被覆盖度、生物量等数据,然后采用定量方法评价工程实施产生的生态效益。结果显示,赤水市水土保持生态修复工程的实施,取得了巨大的生态效益,植被覆盖度、生物多样性、生物量、土壤肥力等都有所增加,而土壤侵蚀、泥沙含量等则大幅减少。     

~7Be含量平衡方法在土壤侵蚀估算中的应用

利用核素示踪技术为研究土壤侵蚀开辟了新的途径,特别是7Be半衰期较短、仅分布于地表几厘米范围内、和土壤颗粒紧密结合等特点,使得其具备了评估短期内地表利用状况改变、水土保持措施等人为活动对地表土壤迁移的影响程度的潜能。介绍了7Be含量平衡方法在短期内土壤侵蚀估算中的应用,指出了该方法的一些不足,并展望了其应用前景。     

7Be示踪技术在土壤侵蚀研究中的应用

摘要：利用放射性核素示踪研究土壤侵蚀已成为国际社会普遍关注的热点问题。^7Be作为一种自然产生的，短寿命的(半衰期53．3d)放射性核素，具有特殊的示踪价值。介绍了^7Be的来源、散落特征及其在土壤颗粒中的存在形态，阐述了^7Be示踪技术现有的土壤侵蚀速率定量估算模型，提出了我国开展^7Be示踪土壤侵蚀过程研究的建议。     

土壤侵蚀模型在水土保持实践中的应用

土壤侵蚀模型是土壤侵蚀理论研究的成果,也是指导水土保持实践的重要工具。本文回顾了美国经验模型USLE、中国经验模型CSLE、美国机理模型WEPP和几个代表性应用模型的发展历程,介绍了土壤侵蚀模型的应用案例,提出几方面启示:土壤侵蚀模型已经成功地应用于区域土壤侵蚀调查与水土保持措施效益评价,还会继续在水土保持措施设计与规划、径流泥沙输移与面源污染、大暴雨事件和重大工程的水土保持效益等生态与环境监测与评估方面发挥更大作用;长期高质量监测与试验是土壤侵蚀模型建立的基础;顶层设计并以管理用户需求为导向建立模型,是实现模型应用的前提;多学科交叉合作和长期坚持,不断与新技术和研究成果融合更新模型,是保持模型有长期生命力的条件。     

流速测量方法研究现状与分析

在土壤侵蚀的发生发展过程中,径流流速和径流量是土壤侵蚀水动力学的重要参数,对评价水土保持措施效益至关重要。但是受径流发生的随机性、泥沙颗粒大小组成和泥沙含量的不确定性,以及野外条件的复杂性等影响,目前还没有具有普适性的径流流速测量技术和方法。从流速测量实际工作出发,对目前常用的流速测量方法的基本原理、适用性和局限性进行了综述,以便有效发挥现有技术优势并选用正确的流速测量仪器设备。此外,针对目前流速测量方法存在的问题,以及径流发生的随机性和过程的复杂性,提出了径流流速实时、自动测量的新方向,期望能为水土保持科学研究和生产实践提供参考。     

区域土壤侵蚀遥感与核素示踪联合评价技术

土壤侵蚀遥感调查具有宏观、快速、信息量大等优点,但是实际应用中有3大制约因素：1）廉价高分辨率影像的获取;2）科学准确的判读和解译方法;3）成熟的土壤侵蚀评价模型或系统的观测数据。我国普遍缺乏土壤侵蚀评价模型和长期观测数据,技术问题比较突出。土壤侵蚀遥感调查中,采用经验分级指标法得出土壤侵蚀现状或强度,影响了土壤侵蚀评价的精度、准确性和应用范围。利用土壤侵蚀核素示踪技术测算不同土地利用单元的土壤侵蚀量,能够突破了遥感土壤侵蚀调查依赖模型和观测数据的限制,实现土壤侵蚀评价的宏观与微观、点与面、估算与实测的结合,为区域土壤侵蚀快速评价提供一条高效途径。     

作为颗粒运移的示踪剂的土壤7Be, 137Cs, 226Ra和228Ra的地球化学种类

A brunisolic soil collected from an erosive forest land(HF-1-1) and a yellow soil from and accumulative shallow basin(HF-6-1) in the watershed of Lake Hongfeng (HF) were used for activity measurements of ^7Be,^137Cs,^226Ra and ^228Ra in different geochemical speciation.More than 85% of ^7Be,^137Cs,^226Ra and 228Ra in the soils were bound to organic Fe-Mn oxy-hydroxide and residual fractions.They could move with soil particlesw and be used as tracers for the erosion and /or accumulation of soil particles.^7Be gohemical specition in the soils agreed with its trace for seasonal particle transport.^137Cs geohemial speciaiton was suitable for tracing soil particle accumulation and for sediment aating.^226Ra and ^228Ra were ombined in crystalline skeleton of clay minerals and mainly remained as residues in the soils and little was bound to the soluble,exchangeable and carbonate fractions.The differentiation of ^226 Ra/^228Ra activity ratios in different geoheical fractions in the soils could be used as a parameter to trace accumulation and /or erosion of soil particles.     

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.     

用137Cs和210Pbex进行中国东北地区土壤侵蚀的评估

Evaluation of soil erosion in agricultural fields is valuable to develop conservation practices for reducing agricultural nonpoint source pollution.Soil erosion rates were quantified using the fallout radionuclide tracer technique in Mojiagou Basin located on the outskirts of Changchun in Northeast China.The calculated soil erosion rates in the study area were 1.99 and 1.85 mm year-1 using 137Cs and excess 210Pb(210Pbex)measurements,respectively.Both fallout radionuclides showed a similar tendency at downslope sites.All measured sites have experienced net erosion during the past 50 to 100 years.137Cs and 210Pbex measurements were useful to quantify soil erosion rates on field and small basin scales.At this rate of erosion,the current fertile topsoil layer would be entirely removed within 70 years.     

径流及泥沙中7Be含量分布与影响因素研究

通过分析次降雨下,来自坡耕地、荒草地、灌木林地径流小区径流、泥沙中7Be含量,发现径流中7Be浓度较小,均值为0.92 Bq/L,但次降雨过程由于受径流量的影响,随径流流失的7Be量较大。坡耕地小区随径流流失7Be占整个小区7Be流失量的11%~33%,对示踪结果影响较大。与地表土壤相比较,侵蚀泥沙中7Be含量较大,尤其是荒草地和灌木林地小区。坡耕地小区侵蚀泥沙颗粒分选性对泥沙中7Be含量影响不明显,它主要受侵蚀类型的影响,面蚀对侵蚀泥沙中7Be含量贡献最大。     

川中丘陵区人工刨地耕作方式下紫色土坡耕地侵蚀速率的137Cs和210Pbex双核素示踪法研究

Purple soils are widely distributed in the Sichuan Hilly Basin and are highly susceptible to erosion, especially on the cultivated slopes. Quantitative assessment of the erosion rates is, however, difficult due to small size of the plots of the manually-tilled land, the complex land use, and steep hillslopes. 137Cs and 210Pbex (excess 210Pb) tracing techniques were used to investigate the spatial pattern of soil erosion rates associated with slope-land under hoe tillage in Neijiang of the Sichuan Hilly Basin. The 137Cs and 210Pbex inventories at the top of the cultivated slope were extremely low, and the highest inventories were found at the bottom of the cultivated slope. By combining the erosion rates estimates provided by both 137Cs and 210Pbex measurements, the weighted mean net soil loss from the study slope was estimated to be 3100 t km-2 year-1, which was significantly less than 6930 t km-2 year-1 reported for runoff plots on a 10°cultivated slope at the Suining Station of soil Erosion. The spatial pattern of soil erosion rates on the steep agricultural land showed that hoe tillage played an important role in soil redistribution along the slope. Also, traditional farming practices had a significant role in reducing soil loss, leading to a lower net erosion rate for the field.     

宁镇地区137Cs与210Pbex 坡面分布特征的地统计学分析

为更加深入地揭示核素示踪土壤侵蚀的内在机理,在Arcgis Geostatistics模块的支持下,运用地统计学方法研究了宁镇地区137Cs与210Pbex的空间异质性及其坡面分布特征。研究结果表明:(1)核素所特有的理化性质决定了137Cs与210Pbex的空间异质性及其坡面分布格局的与众不同。137Cs与210Pbex较大的块金值说明了土壤侵蚀及耕作活动等随机性因素对其空间分布的决定性影响,这正是它们能够示踪土壤侵蚀的原因所在。(2)137Cs属中等程度的空间自相关,其坡面分布格局能够较好地反映出地形这一结构性因素在其中所施加的影响,示踪土壤侵蚀的结果也应更为全面、合理,并具有宏观性。210Pbex的空间相关性很弱,说明其对随机性因素的影响有着更为敏感的响应,在揭示坡面侵蚀的细部特征方面应能做得更好。(3)137Cs与210Pbex坡面分布格局存在较大的差异,这一方面说明两者在初始沉降布局、部分理化性质,以及对各种变异影响因素的响应等诸多方面还存在着不小的差异;另一方面也在提示,两者示踪土壤侵蚀进程的结果很难通过数学模型的调整而达成一致。     

基于137Cs的青藏高原高寒草甸土壤侵蚀及碳流失估算

[目的] 定量分析青藏高原高寒草甸土壤侵蚀状况及其伴随的碳流失,为全面评估土壤侵蚀影响,实施有效水土保持措施提供参考。[方法] 结合¹³⁷Cs示踪技术与前人研究,对青藏高原高寒草甸土壤的整体侵蚀水平及其土壤有机碳流失进行了估算。[结果] 未受人为扰动的高寒草甸土壤自上而下表现出3个层次(A,B和C层)的理化性质特征,其¹³⁷Cs分布遵循显著指数递减模式。目前,高原草甸土壤年均侵蚀模数约为77~230 t/km²,推测其每年直接导致的土壤有机碳损失量平均不低于4.86 t/km²。[结论] 青藏高原高寒草甸土壤侵蚀水平整体较弱,但因土壤侵蚀流失的有机碳不容忽视。在未来气候变化背景下,升温导致的土壤湿度下降对植被生长的限制,以及人类活动的影响,较大可能成为诱使青藏高原草甸土壤退化和有机碳流失的潜在因素。     

固态13C和15N核磁共振法研究15N标记土壤的腐殖质组分

Five humic fractions were obtained from a uniformly ^15N-labelled soil by extraction with 0.1 mol L^-1 Na4P2O7,0.1mol L^-1 NaOH ,and HF/HCl-0.1 mol L^-1 NaOH,consecutively,and analyzed by ^13C and ^15N CPMAS NMR (cross polarization and magic angle spinning nuclear magnetic resonace).Compared with those of native soils humic fractions studied as a whole contained more alkyls ,methoxyls and O-alkyls,being 27%-36%,17%-21%and 36%-40%,respectively,but fewer aromatics and carboxyls(bein 14%-20% and 13%-90%,respectively),Among those humic fractions ,the humic acid(HA)and fulvic acid(FA) extracted by 0.1 mol L^-1 Na4P2O7 contained slightly more carboxyls than corresponding humic fractions extracted by 0.1 mol L^-1 NaOH ,and the HA extacted by 0.1 mol L^-1 NaOH after treatment with HF/HCl contained the least aromatics and carboxyls.The distribution of nitrogen functional groups of soil humic fractions studied was quite similar to each other and also quite similar to that of humic fraction from native soils.More than 75% of total N in each fraction was in amide from,with 9%-13% present as aromatic and /or aliphatic amines and the remainder as heerocyclic N.     

稻秆还田及土壤预淹对施入土壤的(15NH4)2SO4-N的去向及水稻生长的影响

A pot experiment was conducted to investigate the effects of straw incorporation and soil pre-flooding on the fate of (15NH4)2SO4-N and the growth of rice.Excessive application of rice straw when incorporated with(^15 NH4)2 SO4 at the C/N ratio of 40 reduced the loss of (^15NH4)2SO4-N and retarded the growth and development of rice significantly,while no adverse effects were observed on dry weight of panicle and the total recovery of (15NH4)2 SO4-N when rice straw was incorporated with(15NH4)2SO4 at a C/N ratio less than 25.There were no significant effects of duration of soil pre-flooding within 6 weeks on (^15NH4)2 SO4-N uptake by rice and on rice growth,but,less loss of (^15NH4)2SO4-N was observed in the soil with a longer period of pre-flooding.     

7Be在坡面土壤侵蚀中应用的研究进展

7Be是自然界产生的一种放射性核素,半衰期为53.3d,通过干湿沉降到达地表,被土壤颗粒强烈吸附,随土粒的迁移而发生再分布,因此可作为土壤侵蚀的示踪剂。本文就将7Be目前在土壤侵蚀研究中的应用现状做了介绍,并对今后利用7Be示踪土壤侵蚀提出了建议。