应用137Cs示踪技术估算土壤侵蚀的若干问题探讨

[目的]探讨用~(137)Cs示踪技术估算土壤侵蚀量方法(以下简称"~(137)Cs示踪方法")所存在的几个关键问题,促进该方法的标准化和系统化。[方法]对大量已发表的相关文献进行分析,根据作者的研究经验,归纳出~(137)Cs示踪方法在实践应用中所存在的核心问题。[结果]~(137)Cs示踪方法中关于~(137)Cs在空间是均匀分布的假设存在不合理性,不能直接用于定量估算单钻点取样的土壤侵蚀量。~(137)Cs活度的空间变化存在随机性的成分。敏感度和不确定性分析结果证明~(137)Cs活度的空间随机变化量是~(137)Cs示踪方法不确性的最大来源。[结论]可以用多钻点样本平均值来减少~(137)Cs随机变化量所引起的侵蚀估算误差。以统计学为基础的试验设计和采取独立样本的办法可以消除该误差。虽然~(137)Cs模型已被广泛应用,但由于缺乏长期观测资料诸多模型还处在理论研究阶段,没有得到严格的验证和评判。因为不同模型估算的侵蚀量差别甚大,模型验证和筛选对该方法的成功运用至关重要。     

Effects of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on the growth performance,digestive enzymes and selected non‐specific immune responses in sea cucumber,Apostichopus japonicus Selenka

A feeding trial was conducted to evaluate the efficacy of dietary heat‐killed Lactobacillus plantarum L‐137 (HK L‐137) on growth performance, digestive, non‐specific immune and phagocytosis of sea cucumber, Apostichopus japonicus. Sea cucumbers (initial body weight 1.35 ± 0.04 g) were fed diets supplemented with five levels of HK L‐137 (0, 0.005, 0.025, 0.05 and 0.25 g HK L‐137 kg^?1 diets) for 60 days. Results indicated sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher body weight gain and specific growth rate than other groups. Sea cucumbers fed with diets containing 0.05 and 0.25 g HK L‐137 kg^?1 diets showed significantly (P < 0.05) higher protease activity than control group. Higher amylase, lysozyme and phagocytic activities were found in 0.25 g HK L‐137 kg^?1 diet group. Higher superoxide dismutase enzyme and alkaline phosphatase activity was found in 0.05 g HK L‐137 kg^?1. While no significant differences (P > 0.05) were found in acid phosphatase activity. These results suggested that dietary supplementation of 0.05 g HK L‐137 kg^?1 diets would have benefit on growth, digestive enzymes and several non‐specific immune parameters of sea cucumber.     

黑色素细胞中过量表达miR-137对TYRP-1和TYRP-2的影响

【目的】证明miR-137通过调控MITF而间接影响小鼠黑色素细胞TYRP-1和TYRP-2的表达,从而影响黑色素的生成。【方法】通过细胞转染技术在细胞水平过量表达miR-137,对黑色素细胞中黑色素含量进行了测定,经RT-PCR以及western blot检测转染后细胞TYRP-1和TYRP-2在mRNA和蛋白水平的变化。【结果】黑色素含量明显减少,在mRNA水平,TYRP1显著降低至0.4倍,TYRP-2显著降低至0.6倍。在蛋白水平,TYRP-1显著降低至0.61倍,TYRP-2显著降低至0.73倍。【结论】过量表达miR-137会通过调控MITF而使黑色素细胞TYRP-1和TYRP-2的表达量降低,从而揭示了miR-137通过调节TYRP-1和TYRP-2的表达间接调控了黑色素的生成。     

Application of the caesium‐137 technique to soil degradation studies in the Southwestern Highlands of Ethiopia

Soil degradation is a serious problem in the central and northern Highlands of Ethiopia. It has been so for several decades as a result of over exploitation and mismanagement. Relocation of a portion of the population from these regions to the relatively less populated Southwestern Highlands has taken place for decades to try to address the problem. However, such mass resettlements have caused severe soil degradation problems in many destination areas in the Southwestern Highlands. The aim of this study was to assess the problem of soil degradation using the caesium‐137 isotope and to test its value for erosion study in the region. The adapted USLE was applied to compare results from the caesium‐137 isotope studies. Along a deforestation continuum, fields cultivated for various years were studied for erosion. From a reference grazing land plot, total caesium‐137 fallout of 2026 ± 176 Bq m⁻² with a CV of 24·6 per cent was recorded showing the presence of sufficient fallout to apply the technique. Erosion in cultivated fields was estimated against this reference using conversion models. Results from the Proportional Model |−13·9 ± 2·7|and the adapted USLE |12·3 ± 2·6| were not significantly different (p < 0·05), meaning the technique provides reliable results. A positive relationship was observed between severity of erosion and time of cultivation after forest clearing (R² = 0·78). The mean annual loss of soil from cultivated land, 14·9 ± 2·9 t ha⁻¹ y⁻¹, is already beyond the tolerable threshold and might exacerbate further clearing of forests for cultivation if the land is not properly managed. Copyright © 2011 John Wiley & Sons, Ltd.     

中国西南薄层砾石土喀斯特坡地土壤的137Cs分布特点

The fallout radionuclide cesium-137(137 Cs) has been widely employed as a tracer for assessment of soil loss from thick uniform soils;however,few studies have been conducted on thin stony soils on slopes underlain by carbonate rocks which are widely distributed in karst areas.Information derived from 137 Cs measurement of soil samples collected along a carbonate rock slope with thin stony soil where neither soil erosion nor deposition occurred was used to investigate the characteristics of 137 Cs redistribution in a karst area of Southwest China.The results indicated that the 137 Cs inventories of the surface soil on the slope studied were much lower than that of the local 137 Cs reference inventory and the 137 Cs activities were much higher than those on slopes with thick uniform soils.The spatial distribution of 137 Cs inventories was characterized by considerable variation.The high 137 Cs depletion in the stony soil of the slope studied was mainly because a considerable proportion of the fallout input of 137 Cs could be lost with runoff and the dissolution of carbonate particles in the soil promoted the loss of 137 Cs.These demonstrated that the rates of soil loss could not be estimated from the degree of depletion of the 137 Cs inventory relative to the local reference inventory for the thin stony soil of the rocky slope underlain by carbonate rocks in the study area in the way that has been widely used in areas with thick uniform soils.     

中梁山岩溶区坡耕地土壤侵蚀137Cs法研究

采用137Cs法对重庆中梁山岩溶区坡耕地进行了土壤侵蚀研究,结果表明:两个样地顶部侵蚀速率都大于10 000 t/(km2·a),是坡耕地土壤侵蚀最强烈的地方,坡耕地上部侵蚀速率为3 000-4 000 t/(km2·a)左右,而在耕地下部土壤出现堆积.样地多年平均土壤侵蚀速率分别为2 765,3 202 t/(km2·a),其均值相当云贵高原坡耕地土壤侵蚀的40.3%,三峡库区的39.9%,嘉陵江流域的54.1%,黄土高原的39.1%,土壤侵蚀绝对量不大、相对侵蚀强烈是岩溶山区的坡耕地土壤侵蚀的基本特点.     

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。     

东北黑土坡耕地土壤化学计量特征变化对侵蚀的响应

[目的] 探究土壤侵蚀对土壤养分含量及其化学计量比的影响,对于加深认识黑土区坡耕地质量退化过程及防控具有重要意义。[方法] 选择典型黑土区克山县开垦100多年的直形坡和开垦50多年的凸形坡为研究对象,根据¹³⁷Cs示踪技术估算坡耕地土壤侵蚀速率,定量分析土壤侵蚀与土壤有机碳(SOC)、全氮(TN)、全磷(TP)含量及生态化学计量比的关系。[结果] (1)利用¹³⁷Cs示踪法得到坡面整体的年平均侵蚀速率为4 428.56 t/(km²·a),直形坡和凸形坡侵蚀速率平均值分别为3 284.53,5 884.59 t/(km²·a),侵蚀总量分别为3.21×10⁵,2.94×10⁵ t/km²。(2)坡面整体碳氮比(C/N)与SOC呈极显著正相关(p<0.01),碳磷比(C/P)与SOC呈极显著正相关(p＜0.01),氮磷比(N/P)与TP呈极显著负相关(p＜0.01)。直形坡SOC、TN、C/N、C/P和N/P均极显著小于凸形坡养分含量和化学计量比值(p＜0.01),TP含量大于凸形坡TP含量(p＜0.01)。(3)坡面土壤侵蚀空间分布特征与土壤有机碳、全氮及全磷的空间分布具有一致性。坡面土壤侵蚀量与SOC、TN、TP、C/P均呈极显著负相关(p<0.01),与C/N呈显著负相关(p<0.05),与N/P呈负相关但相关性不显著(p>0.05)。[结论] 土壤侵蚀导致坡面土壤SOC、TN和TP在坡面再分布,影响土壤养分化学计量比,造成坡面养分流失严重。     

东北黑土区坡耕地水蚀与风蚀速率的定量区分

用137Cs含量测定和USLE水蚀预报模型,研究了东北黑土区2块坡耕地的水蚀与风蚀速率,结果表明:直型坡耕地和凸型坡耕地的年均侵蚀速率分别为3054和3548t.km2.a-1;由于坡向的不同,2块坡面的风蚀速率分别为631和1155t.km2.a-1,即研究区每年约有0.5～1.0mm的表层土壤被风吹蚀掉,风蚀分别占总侵蚀的20.7%和32.6%;而水蚀仍为研究区主要的侵蚀方式,2块坡面的水蚀速率分别占总侵蚀的79.3%和67.4%。因此,东北黑土区坡耕地水土流失的防治要充分考虑水和风的不同影响,综合治理。     

Using Cs‐137 fingerprinting technique to estimate sediment deposition and erosion rates from Yongkang depression in the karst region of Southwest China

Understanding the erosion and deposition rates is very important for designing soil and water conservation measures. However, existing methods of assessing the rates of soil loss present many limitations and are difficult to apply to in karst areas, and there is still very little data in this areas. Karst depressions comprise geomorphologically important sources and sinks for sediments and can provide the long‐term history records of environmental changes. But there have been few similar studies focused on its sediments in the world. In this paper, the Cs‐137 technique was employed to estimate the sediment deposition rate of karst depression to assess the surface erosion. The results indicate that the average deposition rate, deposition amount and specific deposit yield for the Yongkang catchments since 1963 were estimated to be 4·32 mm y⁻¹, 3·16 t y⁻¹and 20·53 t km⁻² y⁻¹, respectively. The results obtained were consistent with the actual monitoring data of local runoff plots, and confirm the validity of the overall approach. So it was suggested that the mean specific sediment yields of 20 t km⁻² y⁻¹ can be representative of the soil loss rates in the regions. Copyright © 2010 John Wiley & Sons, Ltd.