蒙古高原北部典型草原区土壤风蚀的~(137)Cs示踪法研究

土壤风蚀是蒙古高原北部典型草原区土地退化的主导因素之一.运用137Cs核素示踪技术对蒙古国巴彦淖尔、哈拉和林的不同牧场和弃耕地土壤风蚀速率进行了研究.巴彦淖尔草原牧场、割草场采样点土壤风蚀速率在64.58~169.07t·km-2·a-1之间,均为微度侵蚀水平.哈拉和林弃耕地年均土壤风蚀厚度4.05mm·a-1,风蚀速率为6723.06t·km-2·a-1,达强度侵蚀水平,自20世纪60年代开垦以来,表层土壤累计风蚀损失17.4cm.牧场和弃耕地风蚀速率的差异表明,在蒙古高原北部典型草原区,人为翻动表土,发展种植业,会导致严重的土壤风蚀发生,而传统牧业生产方式对土壤表层扰动较少,未导致破坏性的土壤风蚀发生,对维持生态系统稳定性有重要作用.

蒙古高原塔里亚特-锡林郭勒样带土壤风蚀速率的~(137)Cs示踪分析

运用137Cs示踪技术,查明了蒙古高原西北-东南向的塔里亚特-锡林郭勒样带区域7个典型景观类型采样点风蚀速率及变化特征,分析了不同区域土壤风蚀速率的主要影响因素.研究表明:各采样点137Cs面积活度介于(265.63±44.91)~(1279.54±166.53)Bq·m-2,差异明显,相应的风蚀速率分别为64.58~419.63t·km-2·a-1.样带上蒙古国境内部分,人类活动较轻微,由北向南,随主要的植被景观和气候指标变化,相应的土壤风蚀速率基本呈逐渐加大趋势,表明该区域土壤风蚀过程主要受自然因素的影响和调节;样带上内蒙古锡林浩特和正镶白旗2个典型草原样点风蚀速率为蒙古国巴彦淖尔典型草原样点风蚀速率的近3倍,除导致风蚀加剧的自然条件差异之外,通过比较两地人口密度和载畜量水平,表明人类扰动是导致内蒙古典型草原样点风蚀加剧的主要因素之一.

风蚀土壤剖面(137)~Cs的分布及侵蚀速率的估算

研究137Cs在土壤剖面上的分布是应用137Cs方法定量评价土壤风力侵蚀的基础.以内蒙古太仆寺旗为研究区,采集了4个样点、共62个土壤样本;使用伽马能谱仪测定了各土壤样本的137Cs活度,计算得到各样点的137Cs总量.研究发现不同土地利用类型/土地覆盖等级的137Cs剖面分布特征差异明显.在低覆盖草地和中覆盖草地土壤剖面中,137Cs活度分布形态为负指数分布;在高覆盖草地土壤剖面中,137Cs活度分布形态在剖面上部为单峰状,单峰后继续为负指数分布;在耕地剖面中,137Cs集中在犁底层以上,且均匀分布.对耕地和草地样点分别使用质量平衡模型和剖面分布模型,可以估算得到农耕地、低覆盖草地、中等覆盖草地等3处样点的侵蚀速率分别为7990,4270和1808Mg/km2·a,分别属于强度侵蚀、中度侵蚀和轻度侵蚀,风力侵蚀强度与地面植被覆盖度呈负相关关系.

Estimation of wind erosion rates by using Cs-137 tracing technique: A case study in Tariat-Xilin Gol transect, Mongolian Plateau

Wind erosion is one of the major environmental problems in semi-arid and arid regions. Here we established the Tariat-Xilin Gol transect from northwest to southeast across the Mongolian Plateau, and selected seven sampling sites along the transect. We then estimated the soil wind erosion rates by using the Cs-137 tracing technique and examined their spatial dynamics. Our results showed that the Cs-137 inventories of sampling sites ranged from 265.63 +/- 44.91 to 1279.54 +/- 166.53 Bq.m(-2), and the wind erosion rates varied from 64.58 to 419.63 t.km(-2).a(-1) accordingly. In the Mongolia section of the transect (from Tariat to Sainshand), the wind erosion rate increased gradually with vegetation type and climatic regimes; the wind erosion process was controlled by physical factors such as annual precipitation and vegetation coverage, etc., and the impact of human activities was negligible. While in the China section of the transect (Inner Mongolia), the wind erosion rates of Xilin Hot and Zhengxiangbai Banner were thrice as much as those of Bayannur of Mongolia, although these three sites were all dominated by typical steppe. Besides the physical factors, higher population density and livestock carrying level should be responsible for the higher wind erosion rates in these two regions of Inner Mongolia.

Distribution characteristics of (CS)-C-137 in wind-eroded soil profile and its use in estimating wind erosion modulus

Due to its inert reaction in soil system and distinctive vertical distribution in soil profile, caesium-137 (Cs-137) has been used as a tracer to assess wind erosion. In this study, 62 soil samples were collected from 4 sampling sites in Taipusi County, Inner Mongolia; Caesium-137 activities for those soil samples were measured using a gamma-ray spectrometry in Sichuan University, Chengdu. Distribution pattern of Cs-137 in vertical soil profile was different for different land use and land cover types. Caesium-137 was distributed homogeneously in plow layer of cropland, and negatively exponential in low to medium cover grassland. Distribution pattern in high covered grassland was represented by a peak at 2-4 cm soil depth followed by a negative exponential curve. Based on those findings, simplified mass balance model was chosen to estimate the rate of wind erosion for cropland, while profile distribution model was used for grassland. Estimated wind erosion rates were 7990, 4270 and 1808 Mg(.)km(-2.)a(-1) for cropland, low cover grassland and medium cover grassland, respectively. Wind erosion intensity correlated negatively with plant cover.

红枫湖沉积物~(137)Cs扩散迁移性研究员

保存在湖泊沉积物~(137)Cs剖面中的环境信息记录，可能因~(137)Cs沉积后的再迁移作用而失真。~(137)Cs吸附动力学及离子交换实验表明红枫湖沉积物中的~(137)Cs绝大部分处于固定态，少量处于交换态和造反性吸附态。同时Cs~（+）浓度很低时，高Cs~(+)浓度下在各吸附态与粘土矿物表面的特定吸附部位之间，通常比较明确的对应关系变得有些模糊。本文以界面过程的数学模型为核心，通过模式分析，重建了红枫湖地区历年的~(137)Cs大气沉降通量值，获得了红枫湖集水区 ~(137)Cs流域侵蚀寄宿时间，约为550年。 ~(137)Cs的扩散和其它沉积后再迁移作用。虽然导致~(137)Cs剖面发生了一些变化，但通过适当的数据处理，仍可从中提取出有价值环境信息。