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 ref...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.展开更多
Four sediment cores were collected from Mikawa Bay, Japan, and excess ^210pb and ^137Cs were measured by gamma spectrometry. Sedimentation rates for the four cores were determined by ^210Pb method. The sedimentation r...Four sediment cores were collected from Mikawa Bay, Japan, and excess ^210pb and ^137Cs were measured by gamma spectrometry. Sedimentation rates for the four cores were determined by ^210Pb method. The sedimentation rate range is 0.10-0.70 g/（cm^2.year）. The bio-mixing depth for each core is less than 7.0 cm, and was determined by the excess 210^pb profiles as well. Therefore, the bioturbation is slight. The 210^pb-derived dates coincided with the results from ^137Cs geochronology. Acceleration in sedimentation rate due to environmental alteration has been found in cores A2.5 and 05AS8, representing two depocenters due to their topography. Evidence of the Tokal Flood in 2000 was found in core 05AS8 according to the profiles of both radioisotopes and trace metals.展开更多
The Fukushima nuclear accident in 2011 released large amounts of radionuclides, including ^（137）Cs, into the Pacific Ocean. A quasi-global ocean radioactive transport model with horizontal grid spacing of 0.5°&...The Fukushima nuclear accident in 2011 released large amounts of radionuclides, including ^（137）Cs, into the Pacific Ocean. A quasi-global ocean radioactive transport model with horizontal grid spacing of 0.5°×0.5° and 21 vertical layers was thereafter established to study the long-term transport of the Fukushima-derived ^（137）Cs in the ocean.The simulation shows that the plume of ^（137）Cs would be rapidly transported eastward alongside the Kuroshio Current and its extensions. Contaminated waters with concentrations lower than 2 Bq/m3 would reach the west coast of North America 4 or 5 years after the accident. The ^（137）Cs tends to be carried, despite its very low concentration, into the Indian and South Pacific Oceans by 2016 via various branches of ocean currents.Meanwhile, the ^（137）Cs concentrations in the western part of the North Pacific Ocean decrease rapidly with time. Up to now the highly contaminated waters have remained in the upper 400 m, showing no evidence of significant penetration to deeper layers.展开更多
The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentatio...The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentation rates of Dianchi Lake are determined by ^137Cs dating. However, ^137Cs vertical distribution in sediment cores of Dianchi Lake has special characteristics because Dianchi Lake is located on the southeast of the Qinghai-Tibet Plateau, the Kunming quasi-stationary front is over the borders of Yunnan and Guizhou where the specific precipitation is distributed. Besides 1954, 1963 and 1986 ^137Cs marks can be determined in sediment cores, a ^137Cs mark of 1976 representing the major period of ^137Cs released from China unclear test can be determined and used for an auxiliary dating mark. Meanwhile Dianchi Lake is divided into seven sections based on the water depth, basin topography, hydrological features and supplies of silt and the lakebed area of each section is calculated. The mean annual sedimentation rates for seven sections are 0.0810, 0.1352, 0.1457, 0.1333, 0.0904, 0.1267 and 0.1023 g/cm^2 a in 1963-2003, respectively. The gross sediment accumulation of the lake is 26.18×10^4 t/a in recent 17 years and 39.86×10^4t/a in recent 50 years.展开更多
基金Project supported by the Hundred Talents Program of Chinese Academy of Sciences (No. K09Z3) the National Natural Science Foundation of China (Nos. 40271108 and 40471125).
文摘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.
基金partially benefited from a scholarship from the Ministry of Education, Culture, Sports, Science and Technology, Japana fellowship from the 21st century COE program, Dynamicsof the Sun-Earth-Life Interactive System , Japan (No. G-4).
文摘Four sediment cores were collected from Mikawa Bay, Japan, and excess ^210pb and ^137Cs were measured by gamma spectrometry. Sedimentation rates for the four cores were determined by ^210Pb method. The sedimentation rate range is 0.10-0.70 g/（cm^2.year）. The bio-mixing depth for each core is less than 7.0 cm, and was determined by the excess 210^pb profiles as well. Therefore, the bioturbation is slight. The 210^pb-derived dates coincided with the results from ^137Cs geochronology. Acceleration in sedimentation rate due to environmental alteration has been found in cores A2.5 and 05AS8, representing two depocenters due to their topography. Evidence of the Tokal Flood in 2000 was found in core 05AS8 according to the profiles of both radioisotopes and trace metals.
基金The China-Korea Cooperation Project on the Development of Oceanic Monitoring and Prediction System on Nuclear Safetythe Youth Foundation of the First Institute of Oceanography(FIO),State Oceanic Administration of China,under contract Nos GY0215P01 and GY2015P03+3 种基金the Project of the National Programme on Global Change and Air-sea Interaction under contract No.GASI-03-IPOVAI-05the NSFC-Shandong Joint Fund of Marine Science Research Centers of China under contract No.U1406404the National Natural Science Foundation of China Project under contract No.41506035the KIOST Project under contract No.PE99304
文摘The Fukushima nuclear accident in 2011 released large amounts of radionuclides, including ^（137）Cs, into the Pacific Ocean. A quasi-global ocean radioactive transport model with horizontal grid spacing of 0.5°×0.5° and 21 vertical layers was thereafter established to study the long-term transport of the Fukushima-derived ^（137）Cs in the ocean.The simulation shows that the plume of ^（137）Cs would be rapidly transported eastward alongside the Kuroshio Current and its extensions. Contaminated waters with concentrations lower than 2 Bq/m3 would reach the west coast of North America 4 or 5 years after the accident. The ^（137）Cs tends to be carried, despite its very low concentration, into the Indian and South Pacific Oceans by 2016 via various branches of ocean currents.Meanwhile, the ^（137）Cs concentrations in the western part of the North Pacific Ocean decrease rapidly with time. Up to now the highly contaminated waters have remained in the upper 400 m, showing no evidence of significant penetration to deeper layers.
基金National Natural Science Foundation of China, No.40771186The Key Project of the State Key Laboratory of Soil Sustainable Agriculture,Nanjing Institute of Soil Sciences,Chinese Academy of Sciences,No.5022505
文摘The water quality of Dianchi Lake declines quickly and the eutrophication is getting serious. To identify the internal pollution load of Dianchi Lake it is necessary to evaluate its sediment accumulation. Sedimentation rates of Dianchi Lake are determined by ^137Cs dating. However, ^137Cs vertical distribution in sediment cores of Dianchi Lake has special characteristics because Dianchi Lake is located on the southeast of the Qinghai-Tibet Plateau, the Kunming quasi-stationary front is over the borders of Yunnan and Guizhou where the specific precipitation is distributed. Besides 1954, 1963 and 1986 ^137Cs marks can be determined in sediment cores, a ^137Cs mark of 1976 representing the major period of ^137Cs released from China unclear test can be determined and used for an auxiliary dating mark. Meanwhile Dianchi Lake is divided into seven sections based on the water depth, basin topography, hydrological features and supplies of silt and the lakebed area of each section is calculated. The mean annual sedimentation rates for seven sections are 0.0810, 0.1352, 0.1457, 0.1333, 0.0904, 0.1267 and 0.1023 g/cm^2 a in 1963-2003, respectively. The gross sediment accumulation of the lake is 26.18×10^4 t/a in recent 17 years and 39.86×10^4t/a in recent 50 years.
