137Cs示踪技术研究坡耕地黑土侵蚀和沉积特征

准确地测定研究区137Cs背景值,建立137Cs流失量与土壤再分布速率之间的定量模型是137Cs示踪技术的关键。通过野外选择参照样地和利用热核爆炸源137Cs背景值模型来确定研究区137Cs的背景值,在此基础上用体现耕作迁移的质量平衡模型估算黑土坡耕地不同地貌部位的土壤再分布速率,并对主要参数进行敏感性分析。结果表明(1)研究区实测的137Cs背景值为2376.81±108.46Bq/m2,模型预测值为2318.4Bq/m2,模型预测远离西北核试验基地的地区较为准确。(2)研究区中坡位(坡肩和坡背)137Cs含量最低,侵蚀最为强烈,平均侵蚀速率为33.56t/(hm2·a)和21.67t/(hm2·a);坡麓和坡足则明显表现沉积,平均沉积速率为-4.93t/(hm2·a)和-24.61t/(hm2·a)。(3)模型预测的侵蚀速率与耕层质量深度(d)、张驰深度(H)正相关,而与137Cs年沉降易被迁移的比例(γ)和颗粒校正因子(P)反相关。并且,模型对参数d、p的敏感性分别高于参数H和γ。     

坡耕地紫色土养分空间变异对土壤侵蚀的响应

坡耕地土壤侵蚀导致土壤质量降低,并因此造成对作物产量的不利影响。利用土壤侵蚀测定的^137Cs示踪技术,结合土壤理化分析,研究了川中丘陵区紫色土坡耕地土壤侵蚀所引起的土壤再分配对养分空间变异性的影响。结果表明,川中丘陵区坡耕地土壤侵蚀是水蚀和耕作侵蚀共同作用的结果,强烈的耕作导致坡上部发生最为严重的土壤侵蚀。土壤侵蚀对土壤特性的空间变异性产生深刻影响,坡上部土壤有机质和养分贫瘠,而在坡下部相对富集;土壤有机质、全N、碱解N、有效P、K以及土壤粘粒含量在不同坡位之间出现显著差异。反映净余土壤再分配速率的^137Cs面积浓度与这些土壤理化特性均有密切的相关性。因此,^137Cs面积浓度可以作为表征侵蚀坡地土壤综合质量的指标。     

137Cs和210Pbex示踪黑土区坡耕地土壤侵蚀对有机碳的影响

通过在野外28.5 hm2的坡耕地上采集土壤样品,定量评价了利用137Cs和210Pbex研究土壤有机碳(SOC)动态的潜力,以探讨东北黑土区土壤侵蚀对土壤有机碳的影响.结果表明:农耕地土壤137Cs、210Pbex和SOC在平面和垂直深度上均具有相似的分布特征.在平面上,尽管受土壤侵蚀沉积的影响,137Cs、210Pbex面积活度及SOC储量变异很大,但它们具有相同的变化趋势.在垂直断面上,侵蚀区137Cs、210Pbex和SOC在0～25 cm耕层内分布均匀,25 cm以下放射性活度减小,SOC含量也相应下降;沉积区0～100 cm深度上137Cs和210Pbex呈现先增加后减小的分布规律,SOC也具有类似的变化特征.农耕地SOC与137Cs、210Pbex呈显著线性相关,表明它们在黑土区农耕地上具有相似的物理运移特征,137Cs和210Pbex可直接用来定量评价黑土侵蚀下SOC的时空分布特点.     

桂西北喀斯特坡地土壤137Cs的剖面分布特征及其指示意义

分析了137Cs及土壤有机碳(SOC)在桂西北典型峰丛坡地及岩溶裂隙中的剖面分布特征,探讨了137Cs方法在喀斯特坡地的适用性及其指示的坡面土壤侵蚀特征.结果表明:所有剖面137Cs与SOC均显著相关,两者可能有相同的流失途径;次生林坡地137Cs主体分布深度在24 cm以内,中上及中坡剖面随深度呈指数递减分布,地表无侵蚀或侵蚀轻微,坡脚剖面呈较严重侵蚀形态;坡耕地剖面137Cs在耕层内均匀分布,中上坡及中坡主体分布深度在15 cm左右,面积活度远低于背景值,土壤侵蚀剧烈,坡脚分布深度至45 cm,呈堆积形态;次生林坡脚剖面、耕地中上坡剖面及所有裂隙剖面,137Cs在主体分布深度以下有断续极微量的分布,指示了喀斯特坡地土壤颗粒有随降雨沿地表负地形向地下流失的趋势,但流失量轻微.     

黄土丘陵小流域土地利用变化的土壤侵蚀效应: 基于137Cs示踪的定量评价

基于¹³⁷Cs示踪技术,结合土地利用变化数据,对黄土丘陵沟壑区羊圈沟小流域土壤侵蚀强度的演变过程进行了研究.结果表明：从20世纪80年代以来,该流域土地利用强度逐渐减弱;1980—2006年间,研究区坡耕地面积急剧下降,从94.9 hm²下降到0.2 hm²,乔木林地面积由0增加到51.1 hm²,灌木林地面积由0增加到19.2 hm²,果园林地面积由0增加到18.0 hm²,荒草地面积趋于稳定,由76.9 hm²增加到80.1 hm².研究期间,不同土地利用类型的土壤侵蚀强度依次为:坡耕地>灌木林地>果园林地>荒草地>乔木林地;1980、1984、1996和2006年流域土壤侵蚀强度分别为6408.9、5362.4、4903.9和3641.4 t·km^-2·a^-1,侵蚀程度由强度变为中度.土壤侵蚀强度降低的主要原因是该区的水保措施和植被恢复措施.     

向日葵(Helianthus annuus L.)对133Cs、88Sr的吸收和分布

通过盆栽试验研究了向日葵(Helianthus annuus L.)对土壤中不同处理浓度¹³³Cs和⁸⁸Sr的吸收,以及¹³³Cs和⁸⁸Sr在向日葵不同部位的分布。结果表明：随着处理浓度的增加,植物中¹³³Cs或⁸⁸Sr的含量增加。同一处理浓度下,⁸⁸Sr含量约比¹³³Cs含量高一个数量级。¹³³Cs和⁸⁸Sr在植物不同部位分布不同。根部中¹³³Cs含量高于植物的其他部位（茎、叶、花）。不同于¹³³Cs在植物中的分布,⁸⁸Sr除在根中的分布外,主要转运到了叶片。¹³³Cs和⁸⁸Sr在向日葵体内的分布与目前对放射性¹³⁷Cs和⁹⁰Sr的研究结果相似,所以¹³³Cs和⁸⁸Sr可分别预测¹³⁷Cs和⁹⁰Sr的运转。向日葵是治理大面积低放核素污染土壤的较佳植物种类。     

137Cs技术量化卧龙自然保护区不同生态系统水土保持能力

不同自然植被的水土保持能力可作为制定水土保持目标的重要参考. 通过应用137Cs技术测算卧龙自然保护区不同自然生态系统过去40年的土壤再分配情况, 以此量化可代表不同气候类型的自然植被的水土保持能力. 卧龙保护区地处四川盆地向青藏高原的过渡地带, 植被类型丰富. 研究选取了可以代表适温针阔叶混交林、耐寒落叶针叶林、耐寒灌丛、耐寒常绿针叶林、高山草甸的五个自然生态系统, 每个系统剖面的土壤净侵蚀速率依次是0.17, 0.16, 0.13, 0.11和0.06 kg/(m²·a), 它们的水土保持能力则正好与此顺序相反. 由于降雨量随海拔升高而增加, 使得不同生态系统的¹³⁷CsCs背景值随海拔不同而在1658.2~3707.2 Bq/m²之间变化. 在相似的气候带内制定水土保持策略时, 这些植被的水土保持效果都是必须要参考的.     

典型黑土区侵蚀-沉积对土壤微生物数量空间分布的影响

研究土壤微生物群落对土壤侵蚀-沉积的响应可为农业生态系统功能提升提供重要指导.选择黑龙江省典型薄层黑土区宾县宾州河流域为研究区,分析土壤微生物数量的空间分布特征,并结合137Cs示踪方法估算土壤侵蚀模数,进一步分析坡面和流域尺度土壤侵蚀-沉积对土壤微生物数量的影响.结果表明:季节变化对土壤微生物数量的影响非常明显,夏季...     

桂西北喀斯特坡地土壤137Cs的剖面分布特征及其指示意义

分析了¹³⁷Cs及土壤有机碳（SOC）在桂西北典型峰丛坡地及岩溶裂隙中的剖面分布特征,探讨了¹³⁷Cs方法在喀斯特坡地的适用性及其指示的坡面土壤侵蚀特征.结果表明：所有剖面¹³⁷Cs与SOC均显著相关,两者可能有相同的流失途径;次生林坡地¹³⁷Cs主体分布深度在24 cm以内,中上及中坡剖面随深度呈指数递减分布,地表无侵蚀或侵蚀轻微,坡脚剖面呈较严重侵蚀形态;坡耕地剖面¹³⁷Cs在耕层内均匀分布,中上坡及中坡主体分布深度在15 cm左右,面积活度远低于背景值,土壤侵蚀剧烈,坡脚分布深度至45 cm,呈堆积形态;次生林坡脚剖面、耕地中上坡剖面及所有裂隙剖面,¹³⁷Cs在主体分布深度以下有断续极微量的分布,指示了喀斯特坡地土壤颗粒有随降雨沿地表负地形向地下流失的趋势,但流失量轻微.     

基于RUSLE水蚀模数演算与人工神经网络评价

以黄土高原北部的横山县为例,利用ETM+遥感数据和RUSLE水土流失模型实现了基于“3S”技术的黄土丘陵区水土流失定量反演,并在神经网络技术支持下对定量反演结果进行评价.结果表明,横山县平均水蚀模数为10323 t·hm^-2·yr^-1,年水蚀量为4.38×10⁷ t,总体为中强度水蚀.水蚀程度在空间上呈自西、北向东、南逐渐增强的态势.水蚀随地形部位分异也较为显著,即川坝地、墚峁顶、风沙区地形平坦,以溅蚀为主,有微弱水蚀甚至无水蚀现象;墚峁坡上,坡度平缓,以面蚀为主,为轻度侵蚀;墚峁坡中下部,坡度增大,以线蚀为主,为中度侵蚀;沟缘线以下,坡面陡立,以冲蚀为主,为重度侵蚀.本文研究技术和方法切实可行,具有推广价值,研究结果对流域治理和水土保持具有指导意义.     

137Cs和210Pbex示踪黑土区坡耕地

通过在野外28.5 hm²的坡耕地上采集土壤样品,定量评价了利用¹³⁷Cs和²¹⁰Pb_ex研究土壤有机碳(SOC)动态的潜力,以探讨东北黑土区土壤侵蚀对土壤有机碳的影响.结果表明:农耕地土壤¹³⁷Cs、²¹⁰Pb_ex和SOC在平面和垂直深度上均具有相似的分布特征.在平面上,尽管受土壤侵蚀沉积的影响,¹³⁷Cs、²¹⁰Pb_ex面积活度及SOC储量变异很大,但它们具有相同的变化趋势.在垂直断面上,侵蚀区¹³⁷Cs、²¹⁰Pb_ex和SOC在0～25 cm耕层内分布均匀,25 cm以下放射性活度减小,SOC含量也相应下降;沉积区0～100 cm深度上¹³⁷Cs和²¹⁰Pb_ex呈现先增加后减小的分布规律,SOC也具有类似的变化特征.农耕地SOC与¹³⁷Cs、²¹⁰Pb_ex呈显著线性相关,表明它们在黑土区农耕地上具有相似的物理运移特征,¹³⁷Cs和²¹⁰Pb_ex可直接用来定量评价黑土侵蚀下SOC的时空分布特点.     

Response of changes in soil nutrients to soil erosion on a purple soil of cultivated sloping land

Severe soil erosion of cultivated sloping land in hilly areas of Sichuan, China, has resulted in deterioration of soil quality, and therefore has an adverse impact on crop production. A hillslope of 110 m in length was selected with a slope steepness of 10.12% where the soils were classified as Regosols. Soil samples for determining ¹³⁷Cs, soil organic matter (SOM), total N, P, K, available N, P, K and particle size fraction were collected at 10 m intervals along a transect of the hillslope. Loss of soil nutrients owing to soil erosion was studied by using ¹³⁷Cs technique, and the relationships between ¹³⁷Cs-derived soil redistribution rates and soil nutrients were established over the cultivated sloping land in hilly areas of Sichuan, China (30o26′N, 104o28′E). The values of SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm were smaller at upper and middle slope positions where ¹³⁷Cs inventories were lower (i.e., soil erosion rates were higher) than at downslope positions where ¹³⁷Cs inventories were higher (i.e., soil erosion rates were lower). The lowest ¹³⁷Cs inventories were found at the hilltop, showing that besides erosion owing to water flow, tillage also contributed to soil losses, and intensive tillage was mostly responsible for severe erosion at upper slope positions. There were significant differences in SOM, total N, available N, P, K and the soil particle fractions of size < 0.002 mm between different slope segments, and these properties were significantly correlated with slope length. These soil properties were also significantly correlated with ¹³⁷Cs inventories, indicating that both ¹³⁷Cs and nutrient concentrations varied with topographical changes. The variation in soil properties was strongly influenced by erosion-induced soil redistribution, and therefore ¹³⁷Cs inventories mirroring soil redistribution rates would be considered as an integrated indicator of soil quality.     

Stocks and dynamics of SOC in relation to soil redistribution by water and tillage erosion

Soil organic carbon (SOC) displaced by soil erosion is the subject of much current research and the fundamental question, whether accelerated soil erosion is a source or sink of atmospheric CO₂, remains unresolved. A toposequence of terraced fields as well as a long slope was selected from hilly areas of the Sichuan Basin, China to determine effects of soil redistribution rates and processes on SOC stocks and dynamics. Soil samples for the determination of caesium‐137 (¹³⁷Cs), SOC, total N and soil particle size fractions were collected at 5 m intervals along a transect down the two toposequences. ¹³⁷Cs data showed that along the long slope transect soil erosion occurred in upper and middle slope positions and soil deposition appeared in the lower part of the slope. Along the terraced transect, soil was lost over the upper parts of the slopes and deposition occurred towards the downslope boundary on each terrace, resulting in very abrupt changes in soil redistribution over short distances either side of terrace boundaries that run parallel with the contour on the steep slopes. These data reflect a difference in erosion process; along the long slope transect, water erosion is the dominant process, while in the terraced landscape soil distribution is mainly the result of tillage erosion. SOC inventories (mass per unit area) show a similar pattern to the ¹³⁷Cs inventory, with relatively low SOC content in the erosional sites and high SOC content in depositional areas. However, in the terraced field landscape C/N ratios were highest in the depositional areas, while along the long slope transect, C/N ratios were highest in the erosional areas. When the samples are subdivided based on ¹³⁷Cs‐derived erosion and deposition data, it is found that the erosional areas have similar C/N ratios for both toposequences, while the C/N ratios in depositional areas are significantly different from each other. These differences are attributed to the difference in soil erosion processes; tillage erosion is mainly responsible for high‐SOC inventories at depositional positions on terraced fields, whereas water erosion plays a primary role in SOC storage at depositional positions on the long slope. These data support the theory that water erosion may cause a loss of SOC due to selective removal of the most labile fraction of SOC, while on the other hand tillage erosion only transports the soil over short distances with less effect on the total SOC stock.     

Using 137Cs technique to quantify soil conservation capacities of different ecosystems in Wolong Natural Reserve, southwestern China

Reliable information about soil conservation capacities of different natural ecosystems is an important reference for the design of targeted erosion and sediment control strategies. The objective of this paper is to quantify the soil conservation capacities of different natural ecosystems that can represent different climatic zones. The 137Cs technique has been used to estimate soil redistribution rates in different natural ecosystems over the past 40 years in Wolong Nature Reserve. The reserve, transiting from the Chengdu plain to the Qinghai-Tibet plateau, maintains rich ecosystems from subtropical to frigid.The net soil erosion rates of 5 selected ecosystems that represent a warm coniferous-broadleaf-mixed forest, a cold-resistant deciduous taiga forest, a cold-resistant shrub, an evergreen cold-resistant taiga servation capacities are reversed in order. The reference inventories for 137Cs in different ecosystems velop effective erosion and sediment strategies in areas with similar climates should consider natural ecosystem types.     

黑土坡耕地有机碳及其组分累积-损耗格局对耕作侵蚀与水蚀的响应

耕作与水蚀是黑土区坡耕地碳库退化的主导因素,为进一步探究土壤有机碳(SOC)及其组分对不同侵蚀驱动力(耕作、水力)的响应格局,基于该区耕作侵蚀与水蚀模型,在定量表达耕作侵蚀-沉积量与水蚀量的基础上,利用地统计学的方法,分析了东北黑土区典型漫岗地形坡面尺度SOC及其3种组分的空间分布特征.结果表明: 耕作侵蚀与沉积速率分别表现为坡上>坡下>坡中>坡脚和坡脚>坡下>坡中>坡上;水蚀速率表现为坡下>坡脚>坡中>坡上;坡下陡坡位置耕作侵蚀与水蚀协同引起严重的土壤流失.虽然耕作侵蚀速率(0.02～7.02 t·hm^-2·a^-1)远小于水蚀速率(5.96～101.17 t·hm^-2·a^-1),但耕作侵蚀在全坡面范围均可对SOC产生不同程度的影响,而水蚀则主要在坡下径流汇集区显著影响SOC的累积-损耗.受水蚀与耕作侵蚀-沉积作用影响,SOC、颗粒有机碳、水溶性有机碳在侵蚀点含量低于沉积点,而微生物生物量碳变化趋势相反;耕作侵蚀通过影响颗粒有机碳参与SOC的积累-损耗过程.     

Using 137Cs technique to quantify soil conservation capacities of different ecosystems in Wolong Natural Reserve, southwestern China

Reliable information about soil conservation capacities of different natural ecosystems is an important reference for the design of targeted erosion and sediment control strategies. The objective of this paper is to quantify the soil conservation capacities of different natural ecosystems that can represent different climatic zones. The ¹³⁷Cs technique has been used to estimate soil redistribution rates in different natural ecosystems over the past 40 years in Wolong Nature Reserve. The reserve, transiting from the Chengdu plain to the Qinghai-Tibet plateau, maintains rich ecosystems from subtropical to frigid. The net soil erosion rates of 5 selected ecosystems that represent a warm coniferous-broadleaf-mixed forest, a cold-resistant deciduous taiga forest, a cold-resistant shrub, an evergreen cold-resistant taiga forest, and an alpine meadow are 0.17, 0.16, 0.13, 0.11 and 0.06 kg·m⁻²·a⁻¹, respectively. Their soil conservation capacities are reversed in order. The reference inventories for ¹³⁷Cs in different ecosystems range from 1658 to 3707 Bq·m⁻² with the altitude. Results of this study indicate that any attempt to develop effective erosion and sediment strategies in areas with similar climates should consider natural ecosystem types. Supported by the National Natural Science Foundation of China (Grant No. 40321101)     

The dynamics of soil redistribution and the implications for soil organic carbon accounting in agricultural south‐eastern Australia

Anthropogenically induced change in soil redistribution plays an important role in the soil organic carbon (SOC) budget. Uncertainty of its impact is large because of the dearth of recent soil redistribution estimates concomitant with changing land use and management practices. An Australian national survey used the artificial radionuclide caesium‐137 (¹³⁷Cs) to estimate net (1950s–1990) soil redistribution. South‐eastern Australia showed a median net soil loss of 9.7 t ha^?1 yr^?1. We resurveyed the region using the same ¹³⁷Cs technique and found a median net (1990–2010) soil gain of 3.9 t ha^?1 yr^?1 with an interquartile range from ?1.6 t ha^?1 yr^?1 to +10.7 t ha^?1 yr^?1. Despite this variation, soil erosion across the region has declined as a likely consequence of the widespread adoption of soil conservation measures over the last ca 30 years. The implication of omitted soil redistribution dynamics in SOC accounting is to increase uncertainty and diminish its accuracy.     

Uncertainty in soil carbon accounting due to unrecognized soil erosion

The movement of soil organic carbon (SOC) during erosion and deposition events represents a major perturbation to the terrestrial carbon cycle. Despite the recognized impact soil redistribution can have on the carbon cycle, few major carbon accounting models currently allow for soil mass flux. Here, we modified a commonly used SOC model to include a soil redistribution term and then applied it to scenarios which explore the implications of unrecognized erosion and deposition for SOC accounting. We show that models that assume a static landscape may be calibrated incorrectly as erosion of SOC is hidden within the decay constants. This implicit inclusion of erosion then limits the predictive capacity of these models when applied to sites with different soil redistribution histories. Decay constants were found to be 15–50% slower when an erosion rate of 15 t soil ha^?1 yr^?1 was explicitly included in the SOC model calibration. Static models cannot account for SOC change resulting from agricultural management practices focused on reducing erosion rates. Without accounting for soil redistribution, a soil sampling scheme which uses a fixed depth to support model development can create large errors in actual and relative changes in SOC stocks. When modest levels of erosion were ignored, the combined uncertainty in carbon sequestration rates was 0.3–1.0 t CO₂ ha^?1 yr^?1. This range is similar to expected sequestration rates for many management options aimed at increasing SOC levels. It is evident from these analyses that explicit recognition of soil redistribution is critical to the success of a carbon monitoring or trading scheme which seeks to credit agricultural activities.