Using ^(137)Cs Tracer Technique to Evaluate Erosion and Deposition of Black Soil in Northeast China

Soil and water losses through erosion have been serious in the black soil region of Northeast China. Therefore, a sloping cultivated land in Songnen Plain was selected as a case study to： 1） determine the ^137Cs reference inventory in the study area; 2） calculate erosion and deposition rates of black soil on different slope locations; 3） conduct a sensitivity analysis of some model parameters; and 4） compare overall outputs using four different models. Three transects were set in the field with five slope locations for each transect, including summit, shoulder-slope, back-slope, foot-slope, and toe-slope. Field measurements and model simulation were used to estimate a bomb-derived ^137Cs reference inventory in the study area. Soil erosion and deposition rates were estimated using four ^137Cs models and percentage of ^137Cs loss/gain. The ^137Cs reference value in the study area was 2 232.8 Bq m^-2 with ^137Cs showing a clear topographic pattern, decreasing from the summit to shoulder-slope, then increasing again at the foot-slope and reaching a maximum at the toe-slope, Predicted soil redistribution rates for different slope locations varied. Among models, the Yang Model （YANG-M） overestimated erosion loss but underestimated deposition. However, the standard mass balance model （MBM1） gave predictions similar to a mass balance model incorporating soil movement by tillage （MBM2）. Sensitivity analysis of the proportion factor and distribution pattern of ^137Cs in the surface layer demonstrated the impact of ^137Cs enrichment on calculation of the soil erosion rate. Factors influencing the redistribution of fallout ^137Cs in landscape should be fully considered as calculating soil redistribution rate using ^137Cs technique.

用^(137)Cs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 。

^(137)Cs示踪法研究坡度与土壤流失的关系

应用13 7Cs示踪法对陕西延安燕沟流域自然坡面上坡度与侵蚀强度之间的关系进行了研究。结果表明 ,坡面各点的坡度与侵蚀强度之间呈幂或指数函数关系 ,且相关性极显著 ,即随着坡度的增加 ,侵蚀强度呈幂或指数函数增加 ;偏相关分析结果表明 ,侵蚀强度与坡面平均坡度之间呈正相关关系 ,其相关系数为 0 4447。

基于^(137)Cs示踪法的丹江口小流域农用地土壤侵蚀研究

运用137Cs示踪技术,采用相关土壤侵蚀定量估算模型,探讨丹江口市小流域不同土地利用方式和土壤类型的土壤侵蚀状况。结果表明:研究区137Cs本底值为2 153.46 Bq/m2;耕作土剖面中137Cs呈均一分布,非耕作土剖面中137Cs呈指数递减分布;不同土地利用方式下农用地土壤侵蚀速率从大到小依次为沟谷旱地>坡耕地>菜田>水田>草地;不同土壤类型结合不同地貌形态呈现不同的侵蚀速率,依次为低山丘陵区的石灰土>粘质的黄棕壤土>紫色土和砂质潮土;坡耕地的土壤侵蚀呈现垂直分异特征。

土壤侵蚀^(137)Cs测定的示踪法原理及其常用模型

简要介绍了137Cs示踪法在土壤侵蚀研究中的应用,内容包括137Cs示踪的基本原理,用于耕地及非耕地土壤侵蚀的常用模型,如非耕地的指数分布模型,耕地的比例模型、容量模型和质量平衡模型,同时对以上几种耕地模型的建模假设、计算公式和应用限制进行了对比分析。

用Cs-137示踪法研究浙江天台县典型坡面的土壤侵蚀规律

Cs-137示踪法具有简单、快速、准确的优点,已广泛应用于土壤侵蚀研究。本文在非耕地土壤侵蚀模型的基础上,在浙江省天台县典型区域内,得出Cs-137基准值为2382.02Bq/m^2,土壤Cs-137剖面分布函数为Cs=243.73e^(-0.113:),同时分析了非耕地典型坡面上不同部位的侵蚀与沉积规律。结果表明:土壤侵蚀主要发生在土壤表层20 cm以内的范围,坡地土壤净流失上部大于中下部,在距坡脚附近有土壤沉积现象。坡面不同部位的土壤侵蚀速率并不随着坡长的增加而简单地增大,而是随地表植被结构和覆盖度的不同而变化。

Comprehensive evaluation of heavy metal contamination of sediment in Lake Dianchi by using modified AHP method and ^(137)Cs dating

Through the use of general sampling and measurement by ^(137)Cs dating,problems regarding the absence of monitoring data can easily be resolved.Further,weighted values need to be determined while Environment Quality Comprehensive Index(EQCI)is commonly used as applied in environmental quality comprehensive evaluation.In order to overcome the subjectivity in determining weights,the modified Analytical Hierarchy Process(AHP)method was designed.The modified AHP method involved the following key procedures:First,the parameters y_(i1) and y_(i2) were calculated based on the monitoring data;second,the factors were put in order according to the symbol and value of y_(i1) and y_(i2);third,the continuous odd integers,which represented the importance of factors,were given to factors according to their seating order;and,fourth,the factor weights were determined from the pair-wise comparison matrix calculated by the ratio of the given odd integers.Therefore,the weights were completely based on the monitoring data.In the present study,the comprehensive quality of sediments in five sections of Lake Dianchi were evaluated and the results indicated that the current contamination of sediments in each lake section is much more serious than at any other time in history.

First application of plutonium in soil erosion research on terraces

The spatial distributions of ^(239+240)Pu and ^(137)Cs in soils from Longji Rice Terraces were investigated to evaluate soil erosion.The activity concentrations of ^(239+240)Pu and ^(137)Cs in the surface soils of the paddy fields were in the range of 0.089–0.734 and1.80–7.88 mBq/g,respectively.The activities of ^(239+240)Pu and ^(137)Cs showed very similar distribution trends,first increasing and then decreasing with increasing elevation.The 240Pu/239Pu atom ratios in the surface soils ranged from 0.162 to 0.232.The activities of ^(239+240)Pu and ^(137)Cs in the soil cores tended to be uniformly distributed within the plowed layer and declined exponentially below this depth.The mean soil erosion rates of Longji Rice Terraces estimated by ^(239+240)Pu and ^(137)Cs tracer methods were 5.44 t/(ha·a)and 5.16 t/(ha·a),respectively,which demonstrated that plutonium can replace ^(137)Cs as an ideal tracer for soil erosion research in the future.Landform features are the main factors affecting the distribution of plutonium and ^(137)Cs as well as soil erosion in the Longji Rice Terraces.

不同土地利用方式下农地土壤侵蚀与养分流失

苏南丘陵区存在多种利用当地土地资源方式,诸多利用方式也改变了土壤的性能,一般是人类干预下的耕地的土壤侵蚀及养分流失高于处在自然半自然状态下的非耕地。为了定量了解由土壤侵蚀引起的养分流失,首先应掌握土壤侵蚀的强度,137Cs示踪法可以对此提供帮助。使用此法需解决2个问题:确定研究区域的137Cs背景值与建立估算土壤侵蚀的模型,我们在这方面做了合理的尝试。以此为基础,估算了各种利用方式下土壤养分流失量;为了与黄土和红壤区土壤侵蚀的危害相比较,提出了等值侵蚀模数的概念,以便揭示苏南地区土壤侵蚀的潜在危害性。通过研究初步确认耕地尤其是水田可能是太湖水体营养元素的主要农业来源。

土地利用对红壤丘陵区小流域土壤侵蚀和养分流失的影响

以南方红壤丘陵区两个邻近小流域为对象,结合野外测试、数理模型及^(137)Cs示踪技术,系统分析了各流域土地利用对土壤侵蚀、养分含量及流失量的影响.结果表明,研究区土壤^(137)Cs集中分布于0—40 cm土层,背景值为1823.94 Bq·m^(−2).土壤侵蚀以裸地最为突出(土壤侵蚀量范围为866.11—1809.52 t·km^(−2)·a^(−1)),旱地(137.25—796.43 t·km^(−2)·a^(−1))和茶园(85.17—1616.38 t·km^(−2)·a^(−1))次之,其中,人为干扰下茶园土壤侵蚀量空间差异显著,草地和林地的土壤侵蚀量皆在允许侵蚀范围内(<500 t·km^(−2)·a^(−1)),水田基本不发生侵蚀.土壤有机碳(TOC)、总氮(TN)、总磷(TP)含量具有不同程度的表聚现象,前两者主要来源于植被凋落物,后者受施肥影响为主.人为干扰越强的茶园土壤养分流失量主要受土壤侵蚀影响呈现较大的流失潜力,应予以重点关注.因此,聚焦红壤山区多个邻近小流域土壤侵蚀和养分流失对土地利用的响应研究,可以为我国南方红壤丘陵山区小流域水土保持和面源污染防控提供理论参考.

长江上游紫色土丘陵区小流域地面侵蚀量的确定

紫色土丘陵区小流域地面侵蚀类型主要有面蚀、沟蚀和母质侵蚀三种，本文采用铯－１３７同位素示踪法测算了小流域坡面土壤侵蚀模数的多年平均值；用小区法、径流场法和侵蚀针测法分别测定了相同降雨条件下小流域内面蚀、沟蚀和母质侵蚀的侵蚀模数，进而换算出紫色土丘陵区单元小流域地面侵蚀的多年平均侵蚀模数。所得结果为求取小流域泥沙输移比及预报地面侵蚀量建立了基础。

喀斯特地区水土漏失监测方法评述

水土漏失具有隐蔽性、特殊性和复杂性,有效监测水土漏失是水土漏失研究的难点问题。通过对洞穴滴水示踪、137 Cs同位素示踪、模拟试验、数学模型等水土漏失监测方法的分析,得出以下结论:1)洞穴滴水示踪技术监测获得的水土漏失量普遍偏大;2)137 Cs示踪法在均质土壤条件下可以定量示踪土壤侵蚀,但还不能定量示踪非均质的喀斯特石漠化地区的水土漏失;3)水土漏失模拟试验可以揭示一定的水土漏失机理和规律,试验结论与自然界土壤地下漏失情况有一定偏差,实验结果还难以推广至流域尺度;4)当前已构建的地下漏失数学模型对于地下水土漏失的预测还不够准确,其原因是数学模型中的某个影响因子的获取难度不亚于直接监测水土漏失的困难。鉴于当前水土漏失监测方法的不足,需要从水文地质勘测的方法中寻找合理的水土漏失监测法,建立长期监测的机制,为有效防治和阻控地下水土漏失提供科学依据。