黔西北麻窝山岩溶盆地沉积物断代的质疑

  据谢良胜等的2篇文章报道,黔西北麻窝山岩溶盆地近29年来平均沉积厚度1.33 m,沉积速率4.6 cm/a,流域平均侵蚀模数为2 900.55 t/(km2.a)。而根据笔者的研究成果,该岩溶盆地中央部位沉积物剖面中,表征1963年沉积的137Cs峰值深度为40 cm,减去犁耕层深度,1963年以来的沉积厚度为20 cm,年均沉积速率为0.44 cm/a,此值仅为谢良胜等研究结果4.6 cm/a的1/10。     

Impacts of soil erosion on organic carbon and nutrient dynamics in an alpine grassland soil

The impact of soil erosion on the nutrient dynamics in alpine grassland soils is still an essential problem. Selecting a grass-covered hillslope in eastern Tibet Plateau, the cesium-137 (¹³⁷Cs) technique was used to determine the impacts of soil erosion on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK). The ¹³⁷Cs data revealed that there were distinct soil redistribution patterns in different hillslope positions because of the influences of slope runoff, plant coverage and grazing activity. For the upper slope, soil erosion first decreased downward, followed by soil deposition in its lower part. In contrast, for middle and toe slopes, there was an increasing soil erosion along a downslope transect. Across the lower slope, soil erosion showed an irregular variation. Influenced by the selective transport of water erosion, SOC, TN and TP storage decreased with increasing soil erosion in upper, middle and toe slopes. In contrast, SOC, TN and TP storage varied little with soil erosion in the lower slope. On the whole hillslope, TK storage also varied little with soil erosion due to the large amount of potassium elements derived from soil parent materials. Particularly noteworthy was the greatest storage of SOC, TN and TP in the lower slope where most obvious net soil erosion occurred, which is closely related to the humus accumulation combined with gravel separation as well as weathering and pedogenesis of parent rocks induced by soil freeze-thaw.     

环境放射性核素137Cs和210Pbex的田间原位测定研究

原位现场γ谱仪具有快速准确监测土壤中环境放射性核素137Cs和210Pbex的潜力,可以解决传统环境放射性核素示踪土壤侵蚀在选择参考点和测定时间过长问题。本研究应用现场γ谱仪(ISOCS,In-situObject Counting System),对内蒙古锡林浩特草原土壤中137Cs和210Pbex的含量进行了田间原位(不采样)测定,并与室内γ谱仪测定结果进行了比对。结果显示:现场γ谱仪的探头离地面1m,采用90度准直器,测量时间保证3600s以上时,测定的土壤中137Cs面积浓度与室内测定结果一致,二者的平均偏差为8%,表明现场γ谱仪测定具有较高精度,是快速评价土壤侵蚀速率的有效技术;210Pbex的原位测定结果显著高于室内测定结果,可能由于测定时间较短所致。初步研究结果表明:原位测定具有时间短、精度高的优点,可以克服传统采样造成的空间变异误差。     

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.     

Genotype x environment interaction in the uptake of Cs and Sr from soils by plants

The soil‐plant transfer factors for Cs and Sr were analyzed in relationship to soil properties, crops, and varieties of crops. Two crops and two varieties of each crop: lettuce (Lactuca sativa L.), cv. Salad Bowl Green and cv. Lobjoits Green Cos, and radish (Raphanus sativus L.), cv. French Breakfast 3 and cv. Scarlet Globe, were grown on five different soils amended with Cs and Sr to give concentrations of 1 mg kg^–1 and 50 mg kg^–1 of each element. Soil‐plant transfer coefficients ranged between 0.12–19.10 (Cs) and 1.48–146.10 (Sr) for lettuce and 0.09–13.24 (Cs) and 2.99–93.00 (Sr) for radish. Uptake of Cs and Sr by plants depended on both plant and soil properties. There were significant (P ≤ 0.05) differences between soil‐plant transfer factors for each plant type at the two soil concentrations. At each soil concentration about 60 % of the variance in the uptake of the Cs and Sr was due to soil properties. For a given concentration of Cs or Sr in soil, the most important factor effecting soil‐plant transfer of these elements was the soil properties rather than the crops or varieties of crops. Therefore, for the varieties considered here, soil‐plant transfer of Cs and Sr would be best regulated through the management of soil properties. At each concentration of Cs and Sr, the main soil properties effecting the uptake of Cs and Sr by lettuce and radish were the concentrations of K and Ca, pH and CEC. Together with the concentrations of contaminants in soils, they explained about 80 % of total data variance, and were the best predictors for soil‐plant transfer. The different varieties of lettuce and radish gave different responses in soil‐plant transfer of Cs and Sr in different soil conditions, i.e. genotype x environment interaction caused about 30 % of the variability in the uptake of Cs and Sr by plants. This means that a plant variety with a low soil‐plant transfer of Cs and Sr in one soil could have an increased soil‐plant transfer factor in other soils. The broad implications of this work are that in contaminated agricultural lands still used for plant growing, contaminant‐excluding crop varieties may not be a reliable method for decreasing contaminant transfer to foodstuffs. Modification of soil properties would be a more reliable technique. This is particularly relevant to agricultural soils in the former USSR still affected by fallout from the Chernobyl disaster.     

英国Culm河河漫滩沉积物中磷素时空变化研究

河漫滩上沉积物的沉积伴随着与沉积物相结合的营养和污染物质的沉积。已有研究表明,河漫滩是与沉积物相结合的磷的沉积地。采用137Cs技术,并结合河漫滩沉积物中全磷(TP)含量的剖面信息,可以调查近年河漫滩沉积物中的TP含量,计算TP储量。本文根据英国Devon郡Culm河8个河漫滩采样环沉积物中的数据,重建了在过去40～50年内TP储量和含量的变化。结果表明,在Culm河河漫滩沉积物中,在1963～2000年间TP平均含量为0.60～1.96gkg-1,该值自河流上游向下游和自过去到现在有逐渐增加的趋势;在相同的河漫滩沉积物中,在相同的时期内TP储量为18.62～435.48gm-2,即0.49～11.46gm-2a-1,最大值出现在河流的中游。     

~(137)Cs在卧龙自然保护区土壤中的分布特征

对137Cs在卧龙自然保护区内不同生态系统土壤中的分布特征进行测量分析的结果表明:137Cs在耕地土壤中均匀分布,在其余6种非耕地土壤中呈明显的指数递减分布;非耕地土壤在0~10 cm土层内存在一个137Cs富集层,富集层以下137Cs含量有一个骤降的过程;137Cs在耕地土壤中的分布深度大于耕层厚度20 cm,在非耕地土壤中的分布深度在24 cm左右;137Cs的面积浓度在高山草甸土壤中最大,在适温灌丛土壤中最小,前者是后者的2.6倍。     

CO2浓度升高对美洲商陆富积铯及其根际微生物特征的影响

在开顶式气室(OTC)中采用盆栽试验研究了不同Cs污染浓度(0、100、300、500、1000mg/kg)下,CO2浓度(860μl/L)对美洲商陆(Phytolacca americana Linn.)生物量、Cs富集量及根际土壤微生物的影响。结果表明,与正常CO2浓度相比,CO2浓度升高显著增加美洲商陆地上、地下部分的生物量,其增幅分别为3%~30%和6%~56%;也显著提高了美洲商陆地上、地下部分Cs的含量,最大增幅分别为41%和60%。同时,CO2浓度升高还显著增加美洲商陆根际土壤中细菌、放线菌、真菌的数量,其增幅分别为19%~32%、41%~21%、25%~58%。同一CO2浓度条件下,根际土壤微生物总量与美洲商陆总生物量之间存在显著的相关性。植物生物量、Cs吸收量以及根际土壤微生物量增加,意味着CO2浓度升高有利于利用美洲商陆修复Cs污染土壤。     

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。     

宜兴茶园土壤侵蚀及生态影响

茶园是苏南丘陵坡地的一种典型利用方式 ,其上发生的土壤侵蚀及产生的生态影响不容忽视。而要测度土壤侵蚀 ,137Cs示踪法是目前使用较多的一种有用工具 ,但要用此法 ,需找到研究区的137Cs背景值 ,并建立合适的估算模型。本文在对宜兴茶园研究时 ,确定了这里的137Cs背景值为 2 2 0 0Bqm- 2 ,并建立了估算耕作土壤的较合理的模型h =Hc× (Cref-Ct) /(Cref-Cin)。在此基础上衡量了研究对象的土壤侵蚀量 ;并进一步探讨了由此引发的生态影响 ,包括土层减薄、土壤质地改变和养分流失这样的直接影响 ,以及与之相应的一些间接影响 ,如能耗增加、水体富营养化及土地适宜性变化等 ;并且 ,还采用等值侵蚀模数这个指标 ,在与其他地区尤其是黄土和红壤区比较中揭示了苏南地区土壤侵蚀的生态危害的严重性