青海共和盆地土壤风蚀的^(137)Cs法研究(Ⅰ)——^(137)Cs分布特征

Application of Caesium-137 Technique on Wind Erosion in Gonghe Basin, Qinghai Province (Ⅰ)-^(137)Cs Distribution Characteristics

土壤风蚀作为土地沙漠化的首要环节,对其准确测定和评估是十分迫切和必要的。放射性核素137Cs作为人类核试验的产物,以其独特的理化性质而成为研究土壤侵蚀和泥沙沉积一种良好的示踪源。137Cs法在水蚀研究领域已取得了显著的进展,而在风蚀研究中的应用却相对不足,目前尚处于探索阶段。作者选择青海共和盆地作为研究区,探讨137Cs法在土壤风蚀研究中应用的可行性。通过对共和盆地不同类型土壤剖面的137Cs取样分析,基本查清了区域137Cs分布的若干特性,测定出不同类型土地137Cs活度的排序为:林地>干湖盆>高寒草原>旱作农田≈干草原>固定沙丘>荒漠草原>流动沙丘>风蚀地,137Cs总量的排序为:干湖盆>林地>流动沙丘>高寒草原>旱作农田≈干草原>固定沙丘>荒漠草原>风蚀地。并分析了一些典型剖面的137Cs深度分布及其机制,将137Cs深度剖面划分为正常剖面、沉积剖面、侵蚀剖面和人为扰动剖面4种型式。沙丘砂由于遭受反复吹失和沉积,其137Cs含量逐渐减小,趋于微量的均匀化;而高寒草原的137Cs含量在区域上也较为均匀,在深度分布上,接近负指数分布曲线保存了相对完好的137Cs初始沉积剖面,是理想的137Cs背景值样点。

Wind erosion is the first step to sandy desertification, and it is obvious that the accurate measurement and estimation of wind erosion rate is urgent and essential. Owing to the complexity, randomness and boundlessness of the processes, it is difficult to measure or estimate the wind erosion rate precisely at present. Current methods that include field observation, wind tunnel tests and wind erosion model have some limitations in their practicability, cost and accuracy. The world\|fallout of \{\{\}137Cs\} associated with the nuclear weapons tests during 1950s and 1960s has provided a valuable man\|made tracer for studing soil erosion and sediment delivery. Since its first introduction in the 1970s, \{\{\}137Cs\} technique has received wide application in water erosion research, leading to profound accomplishments. But it was not applied to wind erosion until the 1990s and still remains insufficiency in this respect. Taking the Gonghe Basin in Qinghai Province as the study area, the paper attempts to introduce the \{\{\}137Cs\} method to study soil wind erosion. Through specific sampling strategy and methods, large number of \{\{\}137Cs\} samples with different soil types or land uses are gathered and analyzed. From those \{\{\}137Cs\} data, some \{\{\}137Cs\} distribution characteristics over the whole area are clarified. The 0～30 cm \{\{\}137Cs\} activity of different land types is found to be in the order of woodland>\%playa\%>cold grassland>dry farmland≈dry grassland>fixed dune>desertified grassland>shifted dune>eroded land, while the \{\{\}137Cs\} inventory of different land types is in the order of \%playa\%>woodland>shifting dune>cold grassland>dry farmland≈dry grassland>fixed dune>desertified grassland>eroded land. The \{\{\}137Cs\} distribution in the soil profile can be divided into four types of normal profile, aggrading profile, eroding profile and disturbed profile. The cold grassland that maintained the relatively perfect normal profile of original \{\{\}137Cs\} fallout can be regarded as ideal sampling site of \{\{\}137Cs\} reference.