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1.
This study aims to assess conservation practices in Izta-Popo National Park (Central Mexico) by evaluating the mechanisms of sediment transfer. We applied a methodology based on fallout 137Cs and optically stimulated luminescence (OSL) analysis. This was tested in the upper catchment of Amalacaxco Gorge, selected for being one of the sectors of the park in which man-made actions have been implemented in last decades to favor forest growth in the alpine grassland and to reduce the effect of water runoff. We quantified the 137Cs activity using gamma and beta spectrometry of fine sediment grains extracted from the surface of parcels of 0.4 m2 in areas of natural forest, natural alpine grassland, alpine grassland with conservation practices, ravines and trails. In general, 137Cs values increases as local slope decreases as it was expected. The natural forest is the most stable area in terms of soil erosion and sediment accumulation and, mean 137Cs activity was taken as reference to assess cumulative zones, with higher 137Cs values and erosive, with lower. We found that trails are accumulative surfaces but in other areas, erosion predominates. Man-made ditches, trenches and afforestation in the alpine grassland have higher 137Cs values than the natural grassland, which indicates that conservation practices are limiting the sediment transfer from hillslopes to channels, however, soil retention is less than in the natural grassland. Additionally, we evaluated the luminescence (OSL) values obtained from samples extracted from the sediment transported in ravines that are cutting into different sectors of the study area to assess the grade of resetting of fluvial materials. These luminescence results indicated that the sediment transported in ravines that are cutting into the natural forest and alpine grassland is bleached more efficiently than the sediment transported in the alpine grassland with conservation practices. Results of fallout 137Cs and luminescence strongly suggest that man-made actions in this part of the Izta-Popo National Park are dramatically modifying the natural mechanisms of sediment transfer and favoring soil erosion. We conclude that made ditches, trenches and afforestation are not an effective conservation practice in Amalacaxco Gorge because they are promoting soil erosion instead of reducing it. 相似文献
2.
This study aims to assess conservation practices in Izta-Popo National Park(Central Mexico) by evaluating the mechanisms of sediment transfer. We applied a methodology based on fallout ~(137)Cs and optically stimulated luminescence(OSL) analysis. This was tested in the upper catchment of Amalacaxco Gorge, selected for being one of the sectors of the park in which man-made actions have been implemented in last decades to favor forest growth in the alpine grassland and to reduce the effect of water runoff. We quantified the ~(137)Cs activity using gamma and beta spectrometry of fine sediment grains extracted from the surface of parcels of 0.4 m2 in areas of natural forest, natural alpine grassland, alpine grassland with conservation practices, ravines and trails. In general, ~(137)Cs values increases as local slope decreases as it was expected. The natural forest is the most stable area in terms of soil erosion and sediment accumulation and, mean ~(137)Cs activity was taken as reference to assess cumulative zones, with higher ~(137)Cs values and erosive, with lower. We found that trails are accumulative surfaces but in other areas, erosion predominates. Man-made ditches, trenches and afforestation in the alpine grassland have higher ~(137)Cs values than thenatural grassland, which indicates that conservation practices are limiting the sediment transfer from hillslopes to channels, however, soil retention is less than in the natural grassland. Additionally, we evaluated the luminescence(OSL) values obtained from samples extracted from the sediment transported in ravines that are cutting into different sectors of the study area to assess the grade of resetting of fluvial materials. These luminescence results indicated that the sediment transported in ravines that are cutting into the natural forest and alpine grassland is bleached more efficiently than the sediment transported in the alpine grassland with conservation practices. Results of fallout ~(137)Cs and luminescence strongly suggest that man-made actions in this part of the Izta-Popo National Park are dramatically modifying the natural mechanisms of sediment transfer and favoring soil erosion. We conclude that made ditches, trenches and afforestation are not an effective conservation practice in Amalacaxco Gorge because they are promoting soil erosion instead of reducing it. 相似文献
3.
The radioactive isotope——137 Cs is one of the important tracers for studying the physical processes and the human impacts on the environment. Based on the investigation results of the terrestrial ecosystem of Great Wall Station, Antarctica, it was shown that there are some artificial radioactive elements——137Cs in Antarctic terrestrial ecosystem. The sequence of 137Cs specific activities is as follows: crustaceous lichen>fruticose lichen>surface-moss>surface soil, and the crustaceous lichen is one of the most sensitive ways in monitoring the impact of the long-term diffusion of 137Cs on the environment. 相似文献
4.
137 Cs is an artificial radionuclide with a half-life of 30.2 years,which was released into the environment as a byproduct of atmospheric testing of nuclear weapons during the period of 1950s to 1970s with a peak deposition in 1963.137 Cs fallout was strongly and rapidly adsorbed by soil particles when it deposited on the ground mostly with precipitation.Its following movements will associate with the adsorbed particles.137 Cs tracing technique has been widely used in soil erosion and sedimentation studies since 1980s.This paper introduces the basis of the technique and shows several case studies of assessment of soil erosion rates,investigation of sediment sources and dating of reservoir deposits by using the technique in the Loess Plateau and the Upper Yangtze River Basin. 相似文献
5.
Using neutron activation analysis method we determined contents of rare-earth and radioactive elements (La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Cs, Rb, Sb, Sc, Sr, Ba, U, Th) in source water system of the Changjiang (Yangtze) River, which is mainly composed of the Tuotuo River, the Chumaer River, and the Buqu River. The contents of these elements in the unflltered water have a great variation and a close correlation with the water turbidity. The contents of these elements in filtered water only have a little variation and are lower than those in the unflltered water. The variations in contents of these elements in sediments are also very little. These elements in the unifiltered water are in geometric distribution, except Sc. Most of the elements in sediments are in arithmetic distribution, but Cs, Sb, Th, are in deviation distribution. The contents of most of these elements in the river source area correspond to the contents of fresh water of the earth. Most of these elements have a little variation in their c 相似文献
6.
Geochemical studies of the U, Th, Ra, and40K in surface sediments of the China Sea and adjacent sea areas, the lower reaches of the Huanghe and Changjiang Rivers and
the estuaries of the Zhujiang and Rongjiang Rivers were carried out with a model 8180-4K multichannel Ge(Li)γ spectrometer
in 1981–1985. The mean values of U, Ra, Th,40K are about 2.11 ppm, 7.67×10−13g/g, 11.00 ppm, and 2.33 ppm respectively, in the China Sea, the Okinawa Trough, and the Changjiang and Huanghe River estuaries.
The distribution of the four isotopes is uniform in the above zone.
The contents of U and Th in the sediments of the Zhujiang and Rongjiang Rivers and the Fujian coast are 1–4 times higher than
those of the above zone and are related to the granite and radioactive ore present in the upper reaches of these rivers or
the adjacent mountains.
The distributions of U, Th, Ra, and40K are related to the physico-chemical property, redox state, geological type and grain size of the sediment, and biotic activity.
Contribution No. 1408, Institute of Oceanology, Academia Sinica, Qingdao. 相似文献
7.
The southern sea area of the Huludao City, Liaoning Province might be polluted by heavy metals because it is close to the Jinzhou Bay, one of the heaviest sea area polluted by heavy metals in China. The undisturbed modern sediment core can be used to analyze the accumulation and source of the pollutants using 137 Cs and 210 Pb ex . Thirty-five samples of surface sediment and two core sediments were collected from the southern sea area of Huludao City. The concentrations of copper (Cu), lead (Pb), chrome (Cr), zinc (Zn), arsenic (As) and mercury (Hg) in the surface sediments as well as Cu, Pb, Zn, Cr, 137 Cs and 210 Pb ex in the core sediments were determined to research the spatial distribution and accumulation characteristics, and to analyze the sources and the potential risks of heavy metals. The results show that the pollution levels of Zn and Hg are serious, and 26 stations are at moderate or heavy ecological risks. The concentrations of the heavy metals increase from east to west, as well as from open sea to offshore marine area. The concentrations of heavy metals are not high in the sediments adjacent to the Jinzhou Bay, and the influence caused by the seawater exchange with the Jinzhou Bay is little. The concentrations of the heavy metals in the core sediments show low-high-low characteristic, and it coincides with the pollution history of Huludao City. The atmospheric deposition of heavy metals from the Huludao Zinc Plant is likely to be the main source of pollution without direct discharge of wastewater. The high concentrations of heavy metals appear on the upper sediment of 20 cm. The shallow sediment with high heavy metal contents might be exposed to surface when it was disturbed by the ocean engineering and big storm surge, then cause risk to the safety of aquaculture and human healthy. 相似文献
8.
Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam.To initiate management intervention to reduce sediment yields,there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region(TGRR).The purpose of this study is to use 137 Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR.Cores were taken from a pond and from paddy fields,for 137 Cs measurements.The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm-2 yr-1 and the corresponding amount of sediment deposited is 1,553 t.The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km-2 yr-1 and 2,600 t km-2 yr-1,respectively.Based on the estimated erosion and deposition rates,and the area of each unit,the post 1970 sediment budget for the catchment has been constructed.A sediment delivery ratio of 0.5 has been estimated for the past 42 years.The data indicate that the sloping cultivated lands are the primary sediment source areas,and that the paddy fields are deposition zones.The typical land use pattern(with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields) plays an important role in reducing sediment yield from agricultural catchments in the TGRR.A 137 Cs profile for the sediment deposited in a pond is shown to provide an effective means of estimating the land surface erosion rate in the upstream catchment. 相似文献
9.
Jinqing Liu Ping Yin Yong Zhang Hongying Song Shipu Bi Zhimin Cao Shanshan Liu 《中国海洋大学学报(英文版)》2017,16(5):747-756
Detrital minerals of 137 offshore and 22 river sediment samples collected from Qingdao coastal areas have been analyzed. Four mineral assemblage provinces can be classified by Q-mode cluster analysis. Factor analysis identifies two major factors that account for the total variability in most common minerals: 1) based on the relationship of quartz, hornblende, actinolite, micas, and authigenic pyrite, 41.55% of the variability is related to sediment sources; 2) based on the relationship of epidote, garnet, sphere, and ilmenite, 23.21% can be related to strong hydrodynamic conditions that control transport and sedimentation. By comparing mineral compositions of river waters in the study area, the following four mineral provenances can be identified. The Qingdao-Laoshan nearshore area has a quartz-feldspar-epidote-hornblende-limenite-limonite-sphene assemblage, which is largely attributed to relict sediment and coastal erosion. The Jimo-Haiyang nearshore area has a quartz-feldspar-hornblende-epidote-limonite-mica-actinolite assemblage, derived largely from the Wulong River and Rushan River, and is also affected by the Huanghe River, while the Qianliyan Island area in the deeper offshore area separated by a mud belt has a similar assemblage. The Haiyang-Rushan nearshore area has a quartz-feldspar-hornblende-epidote-micas-limonite assemblage, indicating multiple sources from the Rushan River, the Wulong River, the Huanghe River, and coastal erosion. The central area, located in an eddy center, has a mica-authigenic pyrite-hornblende-quartzfeldspar assemblage, indicating multiple sources dominated by Huanghe River distal sediments. 相似文献
10.
Chronology and nutrients change in recent sediment of Taihu Lake,lower Changjiang River Basin,east China 总被引：1，自引：0，他引：1
Two short sediment cores named ZS and THS dated by the 210Pb or 137Cs method were collected from the northwest and southwest of Taihu Lake respectivly,and total organic carbon(TOC) and nutrients including total nitrogen(TN) and total phosphorus(TP) were determined to analyze the chronology and nutrients change in recent sediment.The results show that 137Cs activities are low(less than 15 Bq/kg) in the two cores,attributed to the 137Cs migration.Based on 210Pb constant rate of supply(CRS) model,the sedimentation accumulation rates range from 0.13 g/(cm2·yr) to 0.76 g/(cm2·yr) in the ZS core,and from 0.10 g/(cm2·yr) to 0.56 g/(cm2·yr) in the THS core.A remarkable increase in organic matter and nutrients has occurred in the two dated cores since the mid-1980s.The historical changes of organic matter and nutrients in the two cores are consisitent with the monitoring data for surface sediment after the 1960s.The TP accumulation rates after the early 1980s are 0.97 and 0.92 times higher than those from the 1950s to the 1980s in ZS and THS cores,respectively.Higher TP concentrations in the past two-decade deposits of Taihu Lake are due to both diagenetic factors and human activities. 相似文献
11.
Jin-zhang Gao Yi Long Xin-bao Zhang Adrian L. Collins Xiu-bin He Yun-qi Zhang Zhong-lin Shi 《山地科学学报》2016,13(5):857-869
Reservoir sedimentation dynamics were interpreted using Cs-137 activity,particle size and rainfall erosivity analysis in conjunction with sediment profile coring.Two sediment cores were retrieved from the Changshou reservoir of Chongqing,which was dammed in 1956 at the outlet of Longxi catchment in the Three Gorges Area using a gravity corer equipped with an acrylic tube with an inner diameter of 6 cm.The extracted cores were sectioned at 2 cm intervals.All sediment core samples were dried,sieved(2 mm) and weighed.137 Cs activity was measured by γ-ray spectrometry.The particle size of the core samples was measured using laser particlesize granulometry.Rainfall erosivity was calculated using daily rainfall data from meteorological records and information on soil conservation history was collated to help interpret temporal sedimentation trends.The peak fallout of 137 Cs in 1963 appeared at a depth of 84 cm in core A and 56 cm in core B.The peaks of sand contents were related to the peaks of rainfall erosivity which were recorded in 1982,1989,1998 and 2005,respectively.Sedimentation rates were calculated according to the sediment profile chronological controls of 1956,1963,1982,1989,1998 and 2005.The highest sedimentation rate was around 2.0 cm?a~(-1) between 1982 and 1988 when the Chinese national reform and the Household Responsibility System were implemented,leading to accelerated soil erosion in the Longxi catchment.Since 1990 s,andparticularly since 2005,sedimentation rates clearly decreased,since a number of soil conservation programs have been carried out in the catchment.The combined use of 137 Cs chronology,particle size and rainfall erosivity provided a simple basis for reconstructing reservoir sedimentation dynamics in the context of both physical processes and soil restoration.Its advantages include avoiding the need for full blown sediment yield reconstruction and the concomitant consideration of core correlation and corrections for autochthonous inputs and reservoir trap efficiency. 相似文献
12.
上泥盆统弗拉斯阶和法门阶界线附近发生了大规模的生物灭绝, 其起因被认为是植物登陆导致的陆地化学风化作用加强及其引起的海洋水体缺氧所致, 但其直接证据还比较缺乏。运用广西地区广泛发育的浅海碳酸盐岩中锶元素(Sr)和同位素(87Sr/86Sr)、铀钍比值(U/Th)记录, 探究了从中泥盆统到下石炭统的陆地化学风化速率及海水氧化还原条件的变化。研究结果表明, 在晚泥盆世(法门阶早期)陆地化学风化作用加强, 导致海水中Sr浓度升高, 及更富集重的Sr同位素组分; 低的U/Th比值也显示该时期水体缺氧严重, 海水中U元素被还原到沉积物中, 导致海水中的U浓度降低。陆地表面化学风化的加强对晚泥盆世海洋水体氧化还原条件的波动以及海洋生物的灭绝有重要影响。 相似文献
13.
通过对济南—淄博—泰安地区地表γ辐射和土壤放射性核素测量,深入研究了其放射性特征、分布规律及其影响因素。结果表明,研究区地表γ辐射剂量率平均值为53.94nGy/h,变化范围为7.00～216.00nGy/h;226 Ra放射性比活度平均值为23.36Bq/kg,232 Th放射性比活度平均值为34.70Bq/kg,40 K放射性比活度平均值为539.36Bq/kg,均低于山东省平均值;研究区内土壤样品天然放射性核素放射性比活度分析结果总体水平不高。地质背景决定地面γ辐射剂量率值,同时环境因素对其剂量率也存在一定影响。研究区年有效剂量当量为0.33mSv,低于公众照射年剂量当量限值1.0mSv,人居环境基本不受影响。 相似文献
14.
Zheng-an Su Dong-hong Xiong Wei Deng Yi-fan Dong Jing Ma C Poudel Padma B Sher Gurung 《山地科学学报》2016,13(10):1829-1839
The Middle Mountains is one of the regions of Nepal most vulnerable to water erosion, where fragile geology, steep topography, anomalous climatic conditions, and intensive human activity have resulted in serious soil erosion and enhanced land degradation. Based on the 137Cs tracing method, spatial variations in soil erosion, organic carbon, and total nitrogen (TN) in terraced fields lacking field banks and forestland were determined. Soil samples were collected at approximately 5 m and 20 m intervals along terraced field series and forestland transects respectively. Mean 137Cs inventories of the four soil cores from the reference site was estimated at 574.33 ± 126.22 Bq m-2 (1 Bq (i.e., one Becquerel) is equal to 1 disintegration per second (1 dps)). For each terrace, the 137Cs inventory generally increased from upper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, 137Cs data showed that abrupt changes in soil erosion rates could occur between the lower part of the upper terrace and the upper part of the immediate terrace within a small distance. This result indicated that tillage erosion is also a dominant erosion type in the sloping farmland of this area. At the same time, we observed a fluctuant decrease in soil erosion rates for the whole terraced toposequence as well as a net deposition at the toe terrace. Although steep terraces (lacking banks and hedgerows) to some extent could act to limit soil sediment accumulation in catchments, soil erosion in the terraced field was determined to be serious. For forestland, with the exception of serious soil erosion that had taken place at the top of slopes due to concentrated flows from a country road situated above the forestland site, spatial variation in soil erosion was similar to the “standard” water erosion model. Soil organic carbon (SOC) and TN inventories showed similar spatial patterns to the 137Cs inventory for both toposequences investigated. However, due to the different dominant erosion processes between the two, we found similar patterns between the <0.002 mm soil particle size fraction (clay sized) and 137Cs inventories in terraced fields, while different patterns could be found between 137Cs inventories and the <0.002 mm soil particle size fraction in the forestland site. Such results confirm that 137Cs can successfully trace soil erosion, SOC and soil nitrogen dynamics in steep terraced fields and forestland in the Middle Mountains of Nepal. 相似文献
15.
西天山温泉地区广泛发育泥盆—石炭纪火山—沉积地层,布拉格达瓦一带出露的托斯库尔他乌组发育一套由滨海间夹陆相—滨浅海相—浅海相过渡的碎屑岩夹火山碎屑岩的沉积建造,沉积物源主要为中酸性火山岩,碎屑颗粒沉积速度较快,属于近源沉积,蚀源区构造环境具活动性质,形成于未切割的活动岛弧。火山岩呈夹层、透镜体状分布于托斯库尔他乌组地层中,火山作用具周期性间歇喷发的特征,岩相表现为爆发—喷溢—沉积—爆发—沉积—爆发的周期性特点。火山岩属钙碱性岩石系列,火山岩浆对应的俯冲深度为上地幔。火山岩微量元素Nb,Sr,P,Ti,Ba为亏损型,Th,Zr元素富集,与岛弧环境密切相关;Nb/Ta为11.96~15.19,略低于原始地幔值,Zr/Hf为30.17~38.20,与原始地幔值相近。稀土总量∑REE为(186.57~208.58)×10-6,轻重稀土比值为5.38~6.13;(Ce/Yb)N为3.90~4.48,(La/Yb)N为4.67~6.70,δEu为0.28~0.49,属于轻稀土富集型,显示为负铕异常。根据沉积物源区分析及主、微量元素特征,结合区域构造背景,认为晚泥盆世托斯库尔他乌组沉积建造所反映的构造环境为消减带俯冲碰撞的岛弧环境。 相似文献
16.
The well-known Three Gorges Dam(TGD) within the Yangtze catchment launched its operation in 2003. The effect of the TGD operation on the sediment size on the East China Sea shelf is rarely known. High resolution(0.5 cm sampling) grain size analysis and 137 Cs and 210 Pb dating of the DH8-1 core were conducted with core collected from the distal part of a main sink for the modern Yangtze sediment entering the sea, the Min-Zhe Coastal Mud Deposits(MZCMD) on the inner East China Sea shelf. The 137 Cs dating results show that the core DH8-1 formed during 1946–2012 with a mean deposition rate of 0.65 cm yr~(-1), indicating that the 0.5 cm sampling for grain size analysis in this local area could reflect environmental changes generally on a one-year time scale. The mean grain size of DH8-1 core sediment that deposited after 2003 is significantly larger than that deposited during 1988–2002. After ruling out other possible factors, we infer that the sediment coarsening of DH8-1 core after 2003 is attributed to the TGD operation which causes the erosion of the Yangtze subaqueous delta. Specifically, the TGD operation significantly intensifies the declining trend of the Yangtze sediment loads to the sea despite no decreased water discharge, which results in extensive erosion of the Yangtze subaqueous delta. The relatively coarse sediment of the subaqueous delta is eroded and resuspended by ocean dynamics and then transported by coastal current, finally depositing on the MZCMD area. In addition, the general sediment fining of core DH8-1 that deposited during 1988–2002, comparing with 1946–1987, is mainly caused by dam construction and soil and water conservation within the Yangtze catchment. Our findings are helpful for better understanding the effects of such a huge dam as the TGD on a sediment sink like the MZCMD of such a large river as the Yangtze River. 相似文献
17.
Acidrainhasbeenaglobalenvironmentalprob-lem.SouthChinaandthesouthwestpartarethetwomainacidrainareasinChinawiththerangeof'pHvariationfrom4.5to4.O,andseientificstudiesonacidrainfocusontheseareas(WANGetal.,l997).Inre-centyears,however,inthenorthpartofChinaacidrainoccurred'notunusuallyandevenmoreseriouslysuchasincitiesofTumenandHunchuninJilinProvince.Itisessentialtodelveintothetemporalandspatialvariationsofatmosphericprecipitationacidityandthevariationscausesintheseareastoprovidesci-entificba… 相似文献
18.
Accelerated soil erosion and land degradation represent major environmental problems for agricultural lands.Reliable information on the rates of soil loss is urgently needed.The traditional techniques for documenting rates of soil loss may meet this need,but face many limitations.The fallout radionuclides,especially 137 Cs and 210 Pb ex,are increasingly used as effective tracers to quantify soil erosion rates,and they represent a valuable complement to the existing classical methods.This paper aims to introduce the basis for assessing soil erosion rates on cultivated and uncultivated slopes by using 137 Cs and 210 Pb ex measurements,to compare the 137 Cs and 210 Pb ex reference inventories,and to report several case studies undertaken in the hilly area of Sichuan Basin and the Three Gorges area of China. 相似文献
19.
利用土壤元素资料2069448个数据,大肠癌死亡调查资料42480例,研究了大肠癌死亡率与土壤环境中砷、镉、钴、铬、铜、氟、汞、锰、镍、铅、硒、钒、锌、锂、钠、钾、铷、铯、银、铍、镁、钙、锶、钡、硼、铝、镓、铟、铊、钪、钇、镧、铈、镨、钕、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钍、铀、锗、锡、钛、锆、铪、锑、铋、钽、碲、钼、钨、溴、碘、铁等61个元素的相关性.结果表明.砷、钒、铯、铊、铀、锑元素与大肠癌死亡率有相关性.等级相关分数分别为-0.5123(p＜0.005),-0.3179(p＜0.05),-0.3190(p＜0.05),-0.4552(p＜0.01),-0.4857(p＜0.005),-0.3232(p＜0.05) 相似文献
20.
根据日照市海岸带2个重点海滩所采集的样品,通过粒度、磁化率、主微量及稀土元素等方面的调查资料,综合分析了研究区沉积物类型、分布特征、搬运路径及物质来源。结果表明,研究区沉积物类型以砂为主,在平行海岸方向上,沉积物粒径自北至南由细变粗。在垂直海岸方向上,从滩肩到滩面再到低潮线处,沉积物粒径逐渐变细。海滨国家森林公园海滩的分选性要好于万平口海水浴场海滩。沉积物受黄海沿岸流影响,多自北向南运移。海滩中浅部物质的来源与陆内一侧基岩中斜长片麻岩和二长花岗岩的关系较为密切,深部物质的来源与靠海一侧基岩中花岗斑岩和花岗闪长岩的关系较为密切。 相似文献