Covering extensive parts of China, Karst landscapes are exceptional because rapid and intensive land use change has caused severe ecosystem degradation within only the last 50 years. The twentieth century intensificat...Covering extensive parts of China, Karst landscapes are exceptional because rapid and intensive land use change has caused severe ecosystem degradation within only the last 50 years. The twentieth century intensification in food production through agriculture has led to a rapid deterioration of soil quality, evidenced in reduced crop production and rapid loss of soil. In many areas, a tipping point appears to have been passed as basement rock is exposed and 'rocky desertification' dominates. Through the establishment of the "Soil processes and ecological services in the karst critical zone of SW China"(SPECTRA)Critical Zone Observatory(CZO) we will endevaour to understand the fundmental processes involved in soil production and erosion, and investigate the integrated geophysical-geochemical-ecological responses of the CZ to perturbations. The CZ spans a gradient from undisturbed natural vegetation through human perturbed landscapes.We seek to understand the importance of heterogeneity insurface and below-ground morphology and flow pathways in determining the spatial distribution of key stocks(soil,C, vegetation, etc.) and their control on ecosystem service delivery. We will assess the extent to which the highly heterogeneous critical zone resources can be restored to enable sustainable delivery of ecosystem services. This paper presents the CZO design and initial assessment of soil and soil organic carbon stocks and evidence for their stability based on caesium-137(^(137) Cs) data.展开更多
Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon(SOC)across a land-use change involving a shift to vegetation with different photosynthetic pathways.Based on the ...Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon(SOC)across a land-use change involving a shift to vegetation with different photosynthetic pathways.Based on the isotopic mass balance equation,relative contributions of new versus old SOC,and SOC turnover rate in corn fields were evaluated world-wide.However,most previous research had not analyzed corn debris left in the field,instead using an average corn plant δ^(13)C value or a measured value to calculate the proportion of corn-derived SOC,either of which could bias results.This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study.The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf.The ^(13)C enrichment sequence in corn plant was tassel﹥stalk or cob﹥root﹥leaves.Individual parts accounting for the total dry mass of corn returned distinct values.Consequently,the average δ^(13)C value of corn does not represent the actual isotopic composition of corn debris.Furthermore,we deduced that the greater the fractionation in corn plant,the greater the possible bias.To alleviate bias of SOC dynamics study,we suggest two measures:analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.展开更多
Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas ...Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent.Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C_4) and from natural vegetation (C_3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C_4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg^(-1) on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment.The increase in the percentage of C_4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C_4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment.展开更多
Rare earth elements(REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that(1)∑ RREEs ranged from119.65 t...Rare earth elements(REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that(1)∑ RREEs ranged from119.65 to 275.33 mg/kg in profile ND and5.11–474.55 mg/kg in profile GTC, with average values of205.79 and 161 mg/kg, respectively. ∑RREEs was higher in accumulation horizon and semi-regolith;(2) Influenced by climate, the fractionation of light and heavy REEs(LREEs and HREEs) varied during weathering. The ratio of LREEs/HREEs in pedosphere was higher than semi-regolith in tropical profile;(3) A negative Eu anomaly in both profiles was the result of bedrock weathering. A positive Ce anomaly was observed in all layers of profile ND, and only in the upper 100 cm of profile GTC. This indicates that redox conditions along the regolith profile varied considerably with climate.(4) Normalized by chondrite,LREEs accumulated much more than HREEs; REE distribution curves were right-leaning with a V-type Eu anomaly in both profiles.展开更多
This study quantifies the surface denudation rate of granitic regolith via the application of the in situ cosmogenic26 Al and10Be depth profile in China. The concentration ranges of26 Al and10Be in the quartz along th...This study quantifies the surface denudation rate of granitic regolith via the application of the in situ cosmogenic26 Al and10Be depth profile in China. The concentration ranges of26 Al and10Be in the quartz along the*3-m granitic regolith profile in Qinhuangdao are(4.9–23.1) 9 105and(2.3–36.6) 9 104atoms/g, respectively. With the exception of the surface sample, both26 Al and10Be concentrations decrease exponentially with sample depth. The Chi-square best-fitting results revealed a total denudation rate of *9 m/Ma averaged over a 103–105a timescale, which is lower than the values observed in global granitic outcrops. Compared with global datasets, the flat terrain due to the lack of tectonic activities is most likely the dominant factor that controls the local denudation process.The surface sample offsets from the theoretical cosmogenic nuclide distribution implies that the denudation rate from river basin sediment could be overestimated because of the bioturbation in the surficial soil layer.展开更多
基金supported by the National Environmental Research Council of the UK(Grant No.NE/N007603/1)the National Science Foundation of China(Grant Nos.41571130042 and 41571130041)
文摘Covering extensive parts of China, Karst landscapes are exceptional because rapid and intensive land use change has caused severe ecosystem degradation within only the last 50 years. The twentieth century intensification in food production through agriculture has led to a rapid deterioration of soil quality, evidenced in reduced crop production and rapid loss of soil. In many areas, a tipping point appears to have been passed as basement rock is exposed and 'rocky desertification' dominates. Through the establishment of the "Soil processes and ecological services in the karst critical zone of SW China"(SPECTRA)Critical Zone Observatory(CZO) we will endevaour to understand the fundmental processes involved in soil production and erosion, and investigate the integrated geophysical-geochemical-ecological responses of the CZ to perturbations. The CZ spans a gradient from undisturbed natural vegetation through human perturbed landscapes.We seek to understand the importance of heterogeneity insurface and below-ground morphology and flow pathways in determining the spatial distribution of key stocks(soil,C, vegetation, etc.) and their control on ecosystem service delivery. We will assess the extent to which the highly heterogeneous critical zone resources can be restored to enable sustainable delivery of ecosystem services. This paper presents the CZO design and initial assessment of soil and soil organic carbon stocks and evidence for their stability based on caesium-137(^(137) Cs) data.
基金financially supported by National Natural Science Foundation of China(Grant No.2013CB95670241573012+1 种基金4157113004141261058)
文摘Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon(SOC)across a land-use change involving a shift to vegetation with different photosynthetic pathways.Based on the isotopic mass balance equation,relative contributions of new versus old SOC,and SOC turnover rate in corn fields were evaluated world-wide.However,most previous research had not analyzed corn debris left in the field,instead using an average corn plant δ^(13)C value or a measured value to calculate the proportion of corn-derived SOC,either of which could bias results.This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study.The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf.The ^(13)C enrichment sequence in corn plant was tassel﹥stalk or cob﹥root﹥leaves.Individual parts accounting for the total dry mass of corn returned distinct values.Consequently,the average δ^(13)C value of corn does not represent the actual isotopic composition of corn debris.Furthermore,we deduced that the greater the fractionation in corn plant,the greater the possible bias.To alleviate bias of SOC dynamics study,we suggest two measures:analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.
基金supported by the National Natural Science Foundation of China(Grant Nos.4157301241571130041 U1612441)
文摘Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent.Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C_4) and from natural vegetation (C_3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C_4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg^(-1) on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment.The increase in the percentage of C_4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C_4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment.
基金funded by National Natural Science Foundation of China(41210004,41603018,41673124 and2013CB956401)ministry of water resources of People’s Republic of China(201401050)
文摘Rare earth elements(REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that(1)∑ RREEs ranged from119.65 to 275.33 mg/kg in profile ND and5.11–474.55 mg/kg in profile GTC, with average values of205.79 and 161 mg/kg, respectively. ∑RREEs was higher in accumulation horizon and semi-regolith;(2) Influenced by climate, the fractionation of light and heavy REEs(LREEs and HREEs) varied during weathering. The ratio of LREEs/HREEs in pedosphere was higher than semi-regolith in tropical profile;(3) A negative Eu anomaly in both profiles was the result of bedrock weathering. A positive Ce anomaly was observed in all layers of profile ND, and only in the upper 100 cm of profile GTC. This indicates that redox conditions along the regolith profile varied considerably with climate.(4) Normalized by chondrite,LREEs accumulated much more than HREEs; REE distribution curves were right-leaning with a V-type Eu anomaly in both profiles.
基金supported by the National Natural Science Foundationof China(41130536,41210004)the State Key Laboratory of Environmental Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences(9014)
文摘This study quantifies the surface denudation rate of granitic regolith via the application of the in situ cosmogenic26 Al and10Be depth profile in China. The concentration ranges of26 Al and10Be in the quartz along the*3-m granitic regolith profile in Qinhuangdao are(4.9–23.1) 9 105and(2.3–36.6) 9 104atoms/g, respectively. With the exception of the surface sample, both26 Al and10Be concentrations decrease exponentially with sample depth. The Chi-square best-fitting results revealed a total denudation rate of *9 m/Ma averaged over a 103–105a timescale, which is lower than the values observed in global granitic outcrops. Compared with global datasets, the flat terrain due to the lack of tectonic activities is most likely the dominant factor that controls the local denudation process.The surface sample offsets from the theoretical cosmogenic nuclide distribution implies that the denudation rate from river basin sediment could be overestimated because of the bioturbation in the surficial soil layer.
