Assessing the contribution of sediments from different sources is essential to understand erosive processes and formulate further soil conservation strategies to address environmental problems.In this study,we combine...Assessing the contribution of sediments from different sources is essential to understand erosive processes and formulate further soil conservation strategies to address environmental problems.In this study,we combined the source fingerprinting approach with geochemistry,including comparison of potential sources,and distribution pattern of major elements,to estimate the different land-use relative contributions to streambed sediment in the Luowugou catchment(13.5 km^2)located on the Heishui River,the first branch of the Jinsha River,China.A total of 57 samples from stream bank,cropland,grassland,forest land,and sediments were collected,and then,15 elements were analyzed foreach sample.The fingerprinting results demonstrated that the stream bank(62.4%)had the greatest relative contribution to the bed sediment yield,while cropland,grassland,and forest land contributed 18.6%,14.9%,and 4.1%to the bed sediments,respectively.In comparison to the fingerprinting method,even though the results upon geochemistry only provide a qualitative assessment,the ranking of sediment contributions based on geochemistry was consistent with the sediment fingerprinting ranking,that is,stream bank>cropland>grassland>forest land.Our findings suggest that the focal point for sediment control practices should be the stream bank rather than cropland in the region.Geochemistry can result in an important means in validating the fingerprinting results.展开更多
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 ...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 137 Cs 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 137 Cs 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 137 Cs inventory generally increased fromupper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, 137 Cs 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, spatialvariation in soil erosion was similar to the "standard" water erosion model. Soil organic carbon(SOC) and TN inventories showed similar spatial patterns to the 137 Cs 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 137 Cs inventories in terraced fields, while different patterns could be found between 137 Cs inventories and the <0.002 mm soil particle size fraction in the forestland site. Such results confirm that 137 Cs can successfully trace soil erosion, SOC and soil nitrogen dynamics in steep terraced fields and forestland in the Middle Mountains of Nepal.展开更多
Soil microorganisms are sensitive indicator of soil health and quality. Understanding the effects of vegetation biomass and seasonal change on soil microorganisms is vital to evaluate the soil quality and implement ve...Soil microorganisms are sensitive indicator of soil health and quality. Understanding the effects of vegetation biomass and seasonal change on soil microorganisms is vital to evaluate the soil quality and implement vegetation restoration. This study analyzed the soil phospholipid fatty acids(PLFAs) in fresh and withered Kudzu(Pueraria montana var. lobata) vegetation conditions in different seasons. The results showed that vegetation biomass and seasonal change significantly affected microbial biomass and its community structure. Both fresh and withered Kudzu cover significantly increased soil microbial biomass, and the growth effect of microbes in the soil with fresh Kudzu cover was more obvious than that with withered Kudzu cover. Compared with the dry season, the rainy season significantly increased the microbial biomass and the B/F(the ratio of bacterial to fungal PLFAs) ratio but dramatically reduced the G+/G-(the ratio of gram-positive to gram-negative bacteria PLFAs). Kudzu cover and seasonal change had a significant effect on microbial structure in soil covered by higher vegetation biomass. Furthermore, soil temperature and moisture had different correlations with specific microbial biomass in the two seasons. Our findings highlight the effect of Kudzu vine cover on the soil microenvironment and soil microhabitat, enhancing the soil quality in the Dry-hot Valley of Jinsha River, Southwest China.展开更多
Land use intensity is a valuable concept to understand integrated land use system, which is unlike the traditional approach of analysis that often examines one or a few aspects of land use disregarding multidimensiona...Land use intensity is a valuable concept to understand integrated land use system, which is unlike the traditional approach of analysis that often examines one or a few aspects of land use disregarding multidimensionality of the intensification process in the complex land system. Land use intensity is based on an integrative conceptual framework focusing on both inputs to and outputs from the land. Geographers’ non-stationary data-analysis technique is very suitable for most of the spatial data analysis. Our study was carried out in the northeast part of the Andhikhola watershed lying in the Middle Hills of Nepal, where over the last two decades, heavy loss of labor due to outmigration of rural farmers and increasing urbanization in the relatively easy accessible lowland areas has caused agricultural land abandonment. Our intention in this study was to ascertain factors of spatial pattern of intensity dynamism between human and nature relationships in the integrated traditional agricultural system. High resolution aerial photo and multispectral satellite image were used to derive data on land use and land cover. In addition, field verification, information collected from the field and census report were other data sources. Explanatory variables were derived from those digital and analogue data. Ordinary Least Square(OLS) technique was used for filtering of the variables. Geographically Weighted Regression(GWR) model was used to identify major determining factors of land use intensity dynamics. Moran’s I technique was used for model validation. GWR model was executed to identify the strength of explanatory variables explaining change of land use intensity. Accordingly, 10 variables were identified having the greatest strength to explain land use intensity change in the study area, of which physical variables such as slope gradient, temperature and solar radiation revealed the highest strength followed by variables of accessibility and natural resource. Depopulation in recent decades has been a major driver of land use intensity change but spatial variability of land use intensity was highly controlled by physical suitability, accessibility and availability of natural resources.展开更多
Controlling aeolian desertification is a key ecological target on the Tibetan Plateau,especially within the widespread river valleys.Vegetation recovery can change the near-soil surface characteristics,which thus may ...Controlling aeolian desertification is a key ecological target on the Tibetan Plateau,especially within the widespread river valleys.Vegetation recovery can change the near-soil surface characteristics,which thus may influence wind erodibility of soils.However,these potential effects are not sufficiently evaluated for aeolian sandy soils.This study selected the Shannan valley of the Yarlung Zangbo River on the southern Tibetan Plateau as a case to investigate the variations in wind erodibility of aeolian sandy soils impacted by different vegetation restoration,since many ecological measures have been implemented in recent decades in the river valley.Eight vegetated sandy lands with different restoration types and ages and two bare sandy lands(as controls)were chosen as test sites.Four vegetated sandy lands were covered by Artemisia wellbyi,Hedysarum scoparium,Sophora moorcroftiana,and Populus L.with the similar restoration age of 10 years.For Sophora moorcroftiana and Populus L.communities,two restoration ages of 6 and over 30 years were also selected respectively.Wind erodibility was reflected by wind erodible fraction(EF),mean weight diameter of dry aggregates(MWD),capillary water capacity(CWC),soil cohesion(CS),and soil penetration resistance(PR)from different aspects.A comprehensive wind erodibility index(CWEI)was further produced by a weighted summation method to combine those five indices together and comprehensively quantify the effects of vegetation restoration on wind erodibility of aeolian sandy soils.The results showed that revegetation was efficient to reduce wind erodibility of aeolian sandy soils.EF generally decreased,while MWD,CWC,CS,and PR increased after vegetation restoration on the aeolian sandy lands.The CWEI of vegetated sandy lands varied greatly from 0.850 to 0 under different restoration types and ages and decreased by 14.4%to 100%compared to the control.Under the four different restoration types,Populus L.had the relatively minimum CWEI,followed by Artemisia wellbyi,Sophora moorcroftiana and Hedysarum scoparium.With succession from 6 to over 30 years,CWEI gradually declined for both the Populus L.and Sophora moorcroftiana restored sandy lands.The decreases in wind erodibility(reflected by CWEI)on vegetated sandy lands were dominantly controlled by the improvement of soil texture and the increases of organic matter and calcium carbonate contents with vegetation restoration.The combined vegetation measure of Populus L.mixed with shrubs and grasses was suggested as the optimal restoration type for mitigating wind erodibility of aeolian sandy soils in the Shannan valley of the Yarlung Zangbo River.展开更多
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA20020401)the Sichuan Science and Technology Program (2018JY0545)+1 种基金the National Basic Research Programme (973 Programme) of China (2015CB452704)the National Natural Science Foundation of China (No. 41571277)
文摘Assessing the contribution of sediments from different sources is essential to understand erosive processes and formulate further soil conservation strategies to address environmental problems.In this study,we combined the source fingerprinting approach with geochemistry,including comparison of potential sources,and distribution pattern of major elements,to estimate the different land-use relative contributions to streambed sediment in the Luowugou catchment(13.5 km^2)located on the Heishui River,the first branch of the Jinsha River,China.A total of 57 samples from stream bank,cropland,grassland,forest land,and sediments were collected,and then,15 elements were analyzed foreach sample.The fingerprinting results demonstrated that the stream bank(62.4%)had the greatest relative contribution to the bed sediment yield,while cropland,grassland,and forest land contributed 18.6%,14.9%,and 4.1%to the bed sediments,respectively.In comparison to the fingerprinting method,even though the results upon geochemistry only provide a qualitative assessment,the ranking of sediment contributions based on geochemistry was consistent with the sediment fingerprinting ranking,that is,stream bank>cropland>grassland>forest land.Our findings suggest that the focal point for sediment control practices should be the stream bank rather than cropland in the region.Geochemistry can result in an important means in validating the fingerprinting results.
基金Financial support for this study was provided by the Aid project on Science and Technology for developing countries from Ministry of Science and Technology of China(2013)the National Natural Science Foundation of China(No.41401313)
文摘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 137 Cs 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 137 Cs 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 137 Cs inventory generally increased fromupper to lower slope positions, accompanied by a decrease in the soil erosion rate. Along the entire terraced toposequence, 137 Cs 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, spatialvariation in soil erosion was similar to the "standard" water erosion model. Soil organic carbon(SOC) and TN inventories showed similar spatial patterns to the 137 Cs 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 137 Cs inventories in terraced fields, while different patterns could be found between 137 Cs inventories and the <0.002 mm soil particle size fraction in the forestland site. Such results confirm that 137 Cs can successfully trace soil erosion, SOC and soil nitrogen dynamics in steep terraced fields and forestland in the Middle Mountains of Nepal.
基金supported by the National Key Research and Development Program of China (2017YFC0505102)the National Basic Research Programme (973 Programme) of China (2015CB452704)+1 种基金the National Natural Science Foundation of China (No.41571277)the Key Programme of the “Western Light” Talents Cultivation programme of the Chinese Academy of Sciences (2014)
文摘Soil microorganisms are sensitive indicator of soil health and quality. Understanding the effects of vegetation biomass and seasonal change on soil microorganisms is vital to evaluate the soil quality and implement vegetation restoration. This study analyzed the soil phospholipid fatty acids(PLFAs) in fresh and withered Kudzu(Pueraria montana var. lobata) vegetation conditions in different seasons. The results showed that vegetation biomass and seasonal change significantly affected microbial biomass and its community structure. Both fresh and withered Kudzu cover significantly increased soil microbial biomass, and the growth effect of microbes in the soil with fresh Kudzu cover was more obvious than that with withered Kudzu cover. Compared with the dry season, the rainy season significantly increased the microbial biomass and the B/F(the ratio of bacterial to fungal PLFAs) ratio but dramatically reduced the G+/G-(the ratio of gram-positive to gram-negative bacteria PLFAs). Kudzu cover and seasonal change had a significant effect on microbial structure in soil covered by higher vegetation biomass. Furthermore, soil temperature and moisture had different correlations with specific microbial biomass in the two seasons. Our findings highlight the effect of Kudzu vine cover on the soil microenvironment and soil microhabitat, enhancing the soil quality in the Dry-hot Valley of Jinsha River, Southwest China.
基金This study was financially supported by the CAS Overseas Institutions Platform Project(Grant No.131C11KYSB20200033)。
文摘Land use intensity is a valuable concept to understand integrated land use system, which is unlike the traditional approach of analysis that often examines one or a few aspects of land use disregarding multidimensionality of the intensification process in the complex land system. Land use intensity is based on an integrative conceptual framework focusing on both inputs to and outputs from the land. Geographers’ non-stationary data-analysis technique is very suitable for most of the spatial data analysis. Our study was carried out in the northeast part of the Andhikhola watershed lying in the Middle Hills of Nepal, where over the last two decades, heavy loss of labor due to outmigration of rural farmers and increasing urbanization in the relatively easy accessible lowland areas has caused agricultural land abandonment. Our intention in this study was to ascertain factors of spatial pattern of intensity dynamism between human and nature relationships in the integrated traditional agricultural system. High resolution aerial photo and multispectral satellite image were used to derive data on land use and land cover. In addition, field verification, information collected from the field and census report were other data sources. Explanatory variables were derived from those digital and analogue data. Ordinary Least Square(OLS) technique was used for filtering of the variables. Geographically Weighted Regression(GWR) model was used to identify major determining factors of land use intensity dynamics. Moran’s I technique was used for model validation. GWR model was executed to identify the strength of explanatory variables explaining change of land use intensity. Accordingly, 10 variables were identified having the greatest strength to explain land use intensity change in the study area, of which physical variables such as slope gradient, temperature and solar radiation revealed the highest strength followed by variables of accessibility and natural resource. Depopulation in recent decades has been a major driver of land use intensity change but spatial variability of land use intensity was highly controlled by physical suitability, accessibility and availability of natural resources.
基金funded by the Second Tibetan Plateau Scientific Expedition and Research Program(2019QZKK0404)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA20020401)the Youth Innovation Promotion Association Program of Chinese Academy of Sciences(2022380)。
文摘Controlling aeolian desertification is a key ecological target on the Tibetan Plateau,especially within the widespread river valleys.Vegetation recovery can change the near-soil surface characteristics,which thus may influence wind erodibility of soils.However,these potential effects are not sufficiently evaluated for aeolian sandy soils.This study selected the Shannan valley of the Yarlung Zangbo River on the southern Tibetan Plateau as a case to investigate the variations in wind erodibility of aeolian sandy soils impacted by different vegetation restoration,since many ecological measures have been implemented in recent decades in the river valley.Eight vegetated sandy lands with different restoration types and ages and two bare sandy lands(as controls)were chosen as test sites.Four vegetated sandy lands were covered by Artemisia wellbyi,Hedysarum scoparium,Sophora moorcroftiana,and Populus L.with the similar restoration age of 10 years.For Sophora moorcroftiana and Populus L.communities,two restoration ages of 6 and over 30 years were also selected respectively.Wind erodibility was reflected by wind erodible fraction(EF),mean weight diameter of dry aggregates(MWD),capillary water capacity(CWC),soil cohesion(CS),and soil penetration resistance(PR)from different aspects.A comprehensive wind erodibility index(CWEI)was further produced by a weighted summation method to combine those five indices together and comprehensively quantify the effects of vegetation restoration on wind erodibility of aeolian sandy soils.The results showed that revegetation was efficient to reduce wind erodibility of aeolian sandy soils.EF generally decreased,while MWD,CWC,CS,and PR increased after vegetation restoration on the aeolian sandy lands.The CWEI of vegetated sandy lands varied greatly from 0.850 to 0 under different restoration types and ages and decreased by 14.4%to 100%compared to the control.Under the four different restoration types,Populus L.had the relatively minimum CWEI,followed by Artemisia wellbyi,Sophora moorcroftiana and Hedysarum scoparium.With succession from 6 to over 30 years,CWEI gradually declined for both the Populus L.and Sophora moorcroftiana restored sandy lands.The decreases in wind erodibility(reflected by CWEI)on vegetated sandy lands were dominantly controlled by the improvement of soil texture and the increases of organic matter and calcium carbonate contents with vegetation restoration.The combined vegetation measure of Populus L.mixed with shrubs and grasses was suggested as the optimal restoration type for mitigating wind erodibility of aeolian sandy soils in the Shannan valley of the Yarlung Zangbo River.