Preliminary results of usingCs to study wind erosion in the Qinghai-Tibet Plateau

The world fallout of caesium-137 (¹³⁷Cs) associated with nuclear weapons testing during the 1950s and 1960s has provided a valuable man-made tracer for studies of soil erosion and sediment delivery. But relatively few researchers have used it to estimate wind erosion. In this paper, the¹³⁷Cs technique is introduced into the study of wind erosion and its modern processes in the Qinghai-Tibet Plateau. Two¹³⁷Cs reference inventories of 982·11 and 2376·04 Bq m⁻²was established preliminarily, which distribute in the south and mid-north parts of the study area respectively. By analysing the patterns of¹³⁷Cs depth profiles from sampling sites, the aeolian processes of erosion and deposition along nearly 40 years has been revealed, i.e. the shrub coppice dunes(S1) and semi-fixed dunefields (S3) had experienced the alternation of erosion and deposition, while the grasslands (S4, S6 and S7) and dry farmlands (S5) suffered erosion only. By using the¹³⁷Cs model, the average wind erosion rates for shrub coppice dune (S1), semi-fixed dunefields (S3), dry farmlands (S5) and grasslands (S4, S6 and S7) were estimated to be 84·14, 69·43, 30·68 and 21·84 tha⁻¹a⁻¹respectively, and for the whole Plateau, averaging 47·59 ha⁻¹a⁻¹which can be regarded as the medium erosion standard. These results derived from¹³⁷Cs for the first time have significant implications for the further research of wind erosion and desertification control in the Qinghai-Tibet Plateau.     

川西北高原的地貌垂直地带性与寒冻夷平面

川西北高原地貌垂直地带性明显：流水地貌带,＜3 800 m；冰缘地貌带,3800～4200 m；冰川地貌带,＞4200 m；相应的主导地貌过程分别是流水侵蚀,冻融侵蚀和冰川侵蚀。本文提出了高原面形成的寒冻夷平机制,并认为川西北高原是大面积构造隆升背景下形成的寒冻夷平地貌。花岗岩和石灰岩等结晶岩抗寒冻风化能力强,形成了冰川发育的高山；三叠系砂板岩,抗寒冻风化能力差,形成了融冻土流发育的丘状起伏的高原面。此外,还延伸联想到青藏高原夷平面和高原隆升的一些科学问题,如冻融侵蚀在高原地貌形成和演化中的作用,地面隆升幅度与地壳构造上升幅度,高原面高度的区域差异和大冰盖问题等。     

ASSESSMENT OF SOIL LOSS ON UNCULTIVATED SLOPE LAND BY USING 137CS TECHNIQUE IN THE UPPER YANGTZE RIVER BASIN OF CHINA

Radionuclides are used as tracers of sediments in areas where no plot data or field monitoring data are not available. Caesium-137 can provide important information on both soil loss rates and sediment sources. The 137Cs technique is employed to assess soil erosion rates in forest and grass lands in the Upper Yangtze River Basin, China. The study area includes 6 forestlands and 4 grasslands in 8 counties and cities over the eastern part of the basin. The ^137Cs reference inventories ranged from 620.9 Bq m-2 to 2560.3 Bq m^-2. For the 6 forestlands, the average 137Cs inventory over a field ranges from 960.8 Bq m^-2 to 2560.3 Bq m^-2. The average erosion rate is estimated from the ^137Cs measurements between 0 to 588 t km^-2yr^-1. For the 4 grasslands, the average ^137Cs inventory ranges from 119.0 Bq m2 to 869.7 Bq m^-2. The average rate of erosion from grassland varies from 0 to 4435 t km^-2 yrl. Where the erosion was more severe, the ^137Cs inventory was lower. The results showed that there is no clear relationship between ^137Cs inventory, slope length and slope gradient on uncultivated land. The erosion rates for uncultivated land and cultivated land is compared. The result indicates that the erosion rates on uncultivated land is much lower than those on cultivated slopes and the severity of the soil erosion is closely related to vegetation cover.     

Decimation and Spectrum Correlation Analysis of Gravity Solid Tide Signal Based on Surface-Simplex Swarm Evolution Optimization Algorithm

In order to reveal the correlation between the harmonic components in the earth's solid tidal wave and the non-correlation superposition relationship, and based on these relations, the tidal harmonic implicit in the gravitational solid tidal signal was analyzed. According to the position relationship among the Earth, the moon and the sun's rotating orbit, an orthogonal decomposition model of tidal force was established. Furthermore, on the orthogonal decomposition model of gravity solid tidal wave based on the independent component analysis of the improved SSSE intelligent optimization algorithm, the spectral correlation method was used to analyze the independent components of gravity solid tidal wave. Thus, the multiplicative demodulation after the orthogonal decomposition of the conformal wave was completely realized. Finally, the above model and algorithm were used to compare and analyze the actual observation data and the theoretical signal as reference background. The results show that the proposed model and method can effectively achieve the orthogonal decomposition of tidal harmonics, highlight the weak energy of the long period harmonics component, and reflect the change of tidal harmonic modulation relationship from the spectral correlation map.     

关于河北平原区深层地下水资源属性的探讨

以河北平原为例,采用同位素、地下水资源评价和地下水水位动态3种思路分析了深层地下水资源属性。根据实测地面沉降量反求深层地下水储存资源量的构成,确定了在以往的深层地下水资源计算时储存资源量少计算了32.77%,弹性释放系数比以往的数据大;根据深层地下水动态特征,分析认为深层地下水资源在同一水文年内可以得到部分恢复,在深层地下水降落漏斗区地下水循环速率将加大,并根据沉积学的观点,认为河北平原含水层在各期古河道带交叉重叠部位或在重叠部位附近可能是连通的,浅层地下水可以沿着各期古河道带沉积的砂性土构成的含水层向下补给深层地下水,其补给量远大于通过巨厚的黏性土层向深层地下水的越流补给。     

Use of caesium-137 measurements to investigate erosion and sediment sources within a small drainage basin in the loess plateau of China

The contributions of sediment from different geomorpholigical units within a small basin in the Loess Plateau have been determined using caesium-137 as a tracer. The mean caesium-137 content of sediment originating from the hill area, where sheet and rill erosion are predominant, was 3–37 Bq kg-1, whereas no caesium-137 was detected in the sediment originating from the gully area where gullying and gravitational erosion are predominant. The mean caesium-137 content of sediment from two flood deposits was 0–23 Bq kg-1 and 0–89 Bq kg-1. The relative contribution from the hill area in the two floods was 7 per cent and 26 per cent, whilst that from the gully area was 93 per cent and 74 per cent.     

DISCUSSION ON APPLYING 137Cs AND 210Pbex FOR LAKE SEDIMENT DATING IN CHINA

137Cs和210Pbex是湖泊沉积物断代常用的两种核素,沉积物中核素的深度分布,不但随核素的大气沉降量变化,也与流域环境变化和沉积后核素的再分布有关.我国环境复杂,人类活动强烈,137Cs和210Pbex深度分布的非理想曲线常见于我国一些湖泊的沉积物.本文简要介绍了湖泊沉积物137Cs和210Pbex深度分布理想曲线和断代基本原理,在参阅大量有关中国湖泊沉积物137Cs和210Pbex断代文献的基础上,讨论了137Cs和210Pbex非理想深度分布曲线的解泽和沉积物断代的几个常见问题.主要观点如下:1)我国湖泊沉积物不存在所谓的1974年和1986年蓄积峰;2)一些湖泊沉积出现的非单峰型137Cs深度分布曲线,可能与人类活动或湖流扰动湖泊底泥、流域侵蚀产沙环境变化和137Cs主要来源于冰川融水补给等因素有关;3)沉积物中的核素垂向运移,不改变剖面中1963年137Cs蓄积峰的位置,不影响其断代标志意义;4)流域环境突发事件引起的沉积剖面中的137Cs和210Pbex明显异常,是断代的可靠标志等.最后介绍了根据沉积剖面137Cs和210Pbex总量与本底值对比,求算沉积速率的核素质量平衡法.     

天津市及其沿海地区地表高程变化现状及趋势

近百年来不同时期的地形图、有关资料的对比研究，揭示天津市及沿海地区的地表高程在20世纪近百年间已发生了明显变化。基于影响沿海地区地表形态的基本参数——保有高程、地面下沉、海面上升和垂直加积速率——所做的预测显示。2030年时天津及沿海地区的地表高程将继续损失，在相伴随的海面上升的共同作用下，预测沼泽化的影响范围将逼近天津市区。