The steeply sloping agricultural highlands in Korea have severe soil erosion.Estimation of both soil erosion and sedimentation in these highlands is necessary to make plans for soil-conservation measures,but it is not...The steeply sloping agricultural highlands in Korea have severe soil erosion.Estimation of both soil erosion and sedimentation in these highlands is necessary to make plans for soil-conservation measures,but it is not feasible using existing soil-erosion models.This study measured the site-specific concentrations of ^(137)Cs and ^(210)Pb_(ex) on both a highland slope(33%slope)and a reference site(undisturbed flat area)to estimate soil erosion and redistribution.The use of the fallout radionuclide(FRN)method was evaluated to see if it is a suitable method for characterizing soil erosion.Results were compared with those obtained with the Universal Soil Loss Equation(USLE),which is an empirical model that estimates annual soil erosion.The average concentrations of ^(137)Cs and ^(210)Pb_(ex) at the reference site were 11.57±0.24 Bq kg^(-1) and 59.74±4.2 Bq kg^(-1),respectively.Concentrations of ^(137)Cs and ^(210)Pb_(ex) in the experimental slope were 16.4%and 10.8%,respectively,of those at the reference site.Radionuclide inventories were lower at the upper point of the slope than those at the basal point of the slope.Concentrations of ^(137)Cs and ^(210)Pb_(ex) were significantly correlated with available phosphorus,organic matter,CEC,and exchangeable cations.Estimation of soil redistribution rate using ^(137)Cs and ^(210)Pb_(ex) showed site-specific variations at different points along the slope,and respective ranges were^(-1)7.46~-207.51 and 1.55~-581.38 Mgha^(-1) yr^(-1),which indicated that more erosion was assessed by ^(210)Pb_(ex) than by ^(137)Cs.Redistribution analysis showed that soil erosion occurred along the entire slope,except for the bottom point of the slope where 1.55 Mgha^(-1) yr^(-1) of sediment accumulated.The USLE provided a single value of the average annual soil loss in the entire slope,which was either 166 or 398 Mgha^(-1) yr^(-1),depending on the soil erodibility factor(soil series factor and calculated factor from soil sample analysis)used in the model.We conclude that the FRN method using ^(137)Cs and ^(210)Pb_(ex) radionuclides can be used to assess soil erosion and redistribution in steeply sloping agricultural highlands.Verification of soil-erosion values using the FRN method and soil-erosion models has been controversial,but it merits further study at many locations with different soils,topography,and management practices.展开更多
In the sedimentary strata dating of estuarial coastal areas,it is often found that there is phenomenon of time-reversal in strata.The seabed sediments could be liquefied under storm waves.A laboratory wave flume exper...In the sedimentary strata dating of estuarial coastal areas,it is often found that there is phenomenon of time-reversal in strata.The seabed sediments could be liquefied under storm waves.A laboratory wave flume experiment demonstrated that storm-induced liquefaction deposits are formed by the oscillations of liquefied sediments.In this paper,the particle size distribution and ^(210)Pb_(ex) specific activity of the sediment samples from the liquefaction disturbed zone and adjacent stable zone of the Yellow River Delta were tested.The stratigraphic divisions based on storm liquefaction deposit sequence can effectively explain the vertical changes in particle size and ^(210)Pb_(ex) specific activity.Due to the differentiation of particles during the storm induced liquefaction,coarse and fine particles regrouped,which could explain the phenomenon of time-reversal in dating data.展开更多
The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constan...The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbse activity in sediments will be exponentially reduced with sedimentation age. 210Pbse in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in- creased, 210Pbse will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pbse dating; on the other hand, the sudden enhancement of 210Pbse flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137 Cs activity is characterized by a tree-peak pat- tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of210Pbse activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha- nism of constraining the transfer of 210Pbse into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de- composition-accumulation”, the sedimentation fluxes （F（Corg）） of organic carbon （Corg） since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbse (F(210Pbse)) in different years display good synchronous relations with the sedimentation flux of organic carbon （F（Corg））, es- pecially in the years of 1972─1974 and 1986─1989. The variation of F（Corg） led to the variation of F(210Pbse); the variation of F（210Pbex） reflects, to some extent, the historical variation of lake pro- ductivity.展开更多
基金This research was supported in part by Research Grant from Kangwon National University(No.520160156:2016)the Korea Ministry of Environment,with the strategic EcoSSSoil Project,KEITI(Korea Environmental Industry and Technology Institute),Korea(Grant No.2019002820004).
文摘The steeply sloping agricultural highlands in Korea have severe soil erosion.Estimation of both soil erosion and sedimentation in these highlands is necessary to make plans for soil-conservation measures,but it is not feasible using existing soil-erosion models.This study measured the site-specific concentrations of ^(137)Cs and ^(210)Pb_(ex) on both a highland slope(33%slope)and a reference site(undisturbed flat area)to estimate soil erosion and redistribution.The use of the fallout radionuclide(FRN)method was evaluated to see if it is a suitable method for characterizing soil erosion.Results were compared with those obtained with the Universal Soil Loss Equation(USLE),which is an empirical model that estimates annual soil erosion.The average concentrations of ^(137)Cs and ^(210)Pb_(ex) at the reference site were 11.57±0.24 Bq kg^(-1) and 59.74±4.2 Bq kg^(-1),respectively.Concentrations of ^(137)Cs and ^(210)Pb_(ex) in the experimental slope were 16.4%and 10.8%,respectively,of those at the reference site.Radionuclide inventories were lower at the upper point of the slope than those at the basal point of the slope.Concentrations of ^(137)Cs and ^(210)Pb_(ex) were significantly correlated with available phosphorus,organic matter,CEC,and exchangeable cations.Estimation of soil redistribution rate using ^(137)Cs and ^(210)Pb_(ex) showed site-specific variations at different points along the slope,and respective ranges were^(-1)7.46~-207.51 and 1.55~-581.38 Mgha^(-1) yr^(-1),which indicated that more erosion was assessed by ^(210)Pb_(ex) than by ^(137)Cs.Redistribution analysis showed that soil erosion occurred along the entire slope,except for the bottom point of the slope where 1.55 Mgha^(-1) yr^(-1) of sediment accumulated.The USLE provided a single value of the average annual soil loss in the entire slope,which was either 166 or 398 Mgha^(-1) yr^(-1),depending on the soil erodibility factor(soil series factor and calculated factor from soil sample analysis)used in the model.We conclude that the FRN method using ^(137)Cs and ^(210)Pb_(ex) radionuclides can be used to assess soil erosion and redistribution in steeply sloping agricultural highlands.Verification of soil-erosion values using the FRN method and soil-erosion models has been controversial,but it merits further study at many locations with different soils,topography,and management practices.
基金funding for this project was provided by the National Natural Science Foundation of China (No.41976049)。
文摘In the sedimentary strata dating of estuarial coastal areas,it is often found that there is phenomenon of time-reversal in strata.The seabed sediments could be liquefied under storm waves.A laboratory wave flume experiment demonstrated that storm-induced liquefaction deposits are formed by the oscillations of liquefied sediments.In this paper,the particle size distribution and ^(210)Pb_(ex) specific activity of the sediment samples from the liquefaction disturbed zone and adjacent stable zone of the Yellow River Delta were tested.The stratigraphic divisions based on storm liquefaction deposit sequence can effectively explain the vertical changes in particle size and ^(210)Pb_(ex) specific activity.Due to the differentiation of particles during the storm induced liquefaction,coarse and fine particles regrouped,which could explain the phenomenon of time-reversal in dating data.
基金supported by the National Natural Science Foundation of China(Grant Nos.40373038 and 49773207)the Natioual Key Basic Research Project(Grant No.2002CB412300)the Nat ional Science Foundation of USA(Grant No.NSF 82-50).
文摘The fundamental assumption of 210Pbsediment dating is the stable flux of 210Pbse, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210Pbse activity in sediments will be exponentially reduced with sedimentation age. 210Pbse in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in- creased, 210Pbse will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210Pbse dating; on the other hand, the sudden enhancement of 210Pbse flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210Pbex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137 Cs activity is characterized by a tree-peak pat- tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of210Pbse activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha- nism of constraining the transfer of 210Pbse into lake sediments. The average atomic ratios of Horg/Corg and Corg/Norg in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de- composition-accumulation”, the sedimentation fluxes （F（Corg）） of organic carbon （Corg） since 1970 were calculated by modeling. The sedimentation fluxes of 210Pbse (F(210Pbse)) in different years display good synchronous relations with the sedimentation flux of organic carbon （F（Corg））, es- pecially in the years of 1972─1974 and 1986─1989. The variation of F（Corg） led to the variation of F(210Pbse); the variation of F（210Pbex） reflects, to some extent, the historical variation of lake pro- ductivity.
