Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion ...Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, northwestern China, to quantify the effects of Artemisia capillaris patterns on runoff and soil loss. The quantitative relationships between runoff/sediment yield and vegetation parameters were also thoroughly analyzed using the path analysis method for identifying the reduction mechanism of vegetation on soil erosion. A simulated rainfall intensity of 90 mm/h was applied on a control plot without vegetation （Co） and on the other three different vegetation distribution patterns： a checkerboard pattern （CP）, a banded pattern perpendicular to the slope direction （BP）, and a single long strip parallel to the slope direction （LP）. Each patterned plot received two sets of experiments, i.e. intact plants and roots only, respectively. All treatments had three replicates. The results showed that all the three other different patterns （CP, BP and LP） of A. capillaris could effectively reduce the runoff and sediment yield. Compared with Co, the other three intact plant plots had a 12%-25% less runoff and 58%-92% less sediment. Roots contributed more to sediment reduction （46%-70%）, whereas shoots contributed more to runoff reduction （57%-81%）. BP and CP exhibited preferable controlling effects on soil erosion compared with LP. Path analysis indicated that root length density and plant number were key parameters influencing runoff rate, while root surface area density and root weight density were central indicators affecting sediment rate. The results indicated that an appropriate increase of sowing density has practical significance in conserving soil and water.展开更多
The development of bare patches typically signifies a process of ecosystem degradation.Within the protection system of Shapotou section of the Baotou-Lanzhou railway,the extensive emergence of bare sand patches poses ...The development of bare patches typically signifies a process of ecosystem degradation.Within the protection system of Shapotou section of the Baotou-Lanzhou railway,the extensive emergence of bare sand patches poses a threat to both stability and sustainability.However,there is limited knowledge regarding the morphology,dynamic changes,and ecological responses associated with these sand patches.Therefore,we analyzed the formation and development process of sand patches within the protection system and its effects on herbaceous vegetation growth and soil nutrients through field observation,survey,and indoor analysis methods.The results showed that sand patch development can be divided into three stages,i.e.,formation,expansion,and stabilization,which correspond to the initial,actively developing,and semi-fixed sand patches,respectively.The average dimensions of all sand patch erosional areas were found to be 7.72 m in length,3.91 m in width,and 0.32 m in depth.The actively developing sand patches were the largest,and the initial sand patches were the smallest.Throughout the stage of formation and expansion,the herbaceous community composition changed,and the plant density decreased by more than 50.95%.Moreover,the coverage and height of herbaceous plants decreased in the erosional area and slightly increased in the depositional lobe;and the fine particles and nutrients of soils in the erosional area and depositional lobe showed a decreasing trend.In the stabilization phases of sand patches,the area from the inlet to the bottom of sand patches becomes initially covered with crusts.Vegetation and 0-2 cm surface soil condition improved in the erosional area,but this improvement was not yet evident in the depositional lobe.Factors such as disturbance,climate change,and surface resistance to erosion exert notable influences on the formation and dynamics of sand patches.The results can provide evidence for the future treatment of sand patches and the management of the protection system of Shapotou section of the Baotou-Lanzhou railway.展开更多
Extremely hot environments can trigger serious health problems.To evaluate the effects of microclimate on thermal comfort,we proposed and validated a modified thermal humidity index(MTHI)that combined air temperature ...Extremely hot environments can trigger serious health problems.To evaluate the effects of microclimate on thermal comfort,we proposed and validated a modified thermal humidity index(MTHI)that combined air temperature and relative humidity with land surface temperature(LST).MTHI was more sensitive to microclimate changes than the general thermal humidity index that includes only T and RH,and thus the thermal comfort could be better indicated.In an urban riparian buffer study,we estimated the temporal dynamics and spatial distribution of MTHI values for 47 vegetation patches and explored how structural characteristics of patches affect the thermal comfort.The results showed that planting could significantly reduce LST and MTHI.Vegetation patches with complex vertical structures had considerably higher thermal comfort than those with simple structures.Decreasing nearest distance to river or increasing plant abundance could reduce the thermal discomfort.There were significant differences in the structure characteristics between the patches with MTHI<70 and those with MTHI>70,implying the critical thresholds of variations in thermal comfort with patch structure.Given that people always feel uncomfortable during the daytime in July,optimizing the patch structure is essential to improve the microclimate regulation services of an urban landscape.展开更多
In natural rivers,patches of vegetation generally expand over their steady wake region in the streamwise direction,forming elongated patches with length(L)greater than their width(b).This paper studies how the wake fl...In natural rivers,patches of vegetation generally expand over their steady wake region in the streamwise direction,forming elongated patches with length(L)greater than their width(b).This paper studies how the wake flows and the vortices develop as the emergent patches expand their length in the streamwise direction.The patches are modeled with the same width but different lengths in laboratory experiments.Behind the patches,the steady wake region(L_(w))is not related to the width-related flow blockage(C_(d)ab),where C_(d) is the drag coefficient,a is the vegetation density.Instead,L_(w) is related to the length-related flow blockage(C_(d)aL).On this basis,a model is proposed for predicting L_(w),which is in good agreement with the measurements.As a patch becomes denser and/or longer(as C_(d)aL increases),the steady wake region becomes shorter(L_(w) decreases),and vortices are observed closer to the patch trailing edge,producing a turbulence of a greater magnitude beyond L_(w).When the flow blockage increases to the limit(C_(d)aL>8),the Karman vortices are observed directly behind the porous patches.These results can be used to explain the longitudinal elongation of the vegetation patches in the field.展开更多
The hydraulic characteristics in an open channel with vegetation are very important in controlling the environment pollution and restoring the river ecology. This paper studies the influence of the bed form and the ve...The hydraulic characteristics in an open channel with vegetation are very important in controlling the environment pollution and restoring the river ecology. This paper studies the influence of the bed form and the vegetation patch density on the spatial velocity pattern. Rigid fiberglass circular cylinders are used to simulate the vegetation and a 3-D acoustic Doppler velocimeter (ADV) is used to measure the local flow velocities. Two types of bed forms and a series of vegetation patch densities are considered. The experimental results show that the bed form significantly influences the vertical distribution of the streamwise velocity. Besides, the velocity is affected by the bed form while the lateral distribution shape of the streamwise velocity as well as the lateral and longitudinal distribution shapes of the depth-averaged velocity is less affected. When all test conditions but the bed condition remain the same, as a result of the water energy consumption by the sediment movement, the velocity in the mobile bed case is smaller than that in the rigid bed case. The vegetation patch density has a significant effect on the flow velocity. The distributions of the flow velocity at different locations show different trends with the increase of the vegetation patch density. The upstream adjustment length is not affected by the vegetation patch density, but the steady wake length is very much affected.展开更多
A staggered distribution of vegetation is very common in nature,which might significantly affect the flow structure.To investigate its impact,three rows of staggered vegetation groups are designed under seven differen...A staggered distribution of vegetation is very common in nature,which might significantly affect the flow structure.To investigate its impact,three rows of staggered vegetation groups are designed under seven different working conditions.The horizontal and vertical distances between the vegetation groups are constant,while the vegetation density is variable.The flow field is measured by the acoustic Doppler velocimeter(ADV).It is indicated that both the patch exit velocity and the steady wake velocity decrease with the increase of the density,which is also related to the vegetation rows.Except for the first patch,the upstream adjustment regions of all patches are diminished to some extent,due to the effect of the contralateral patch.The steady wake region also shows a decreasing trend,with a reduction of 0.5D each time when the water flows through the patch.This means that the flow structure is also affected by the number of vegetation rows.The intensity of the turbulence increases along the channel and has a non-axisymmetric distribution similar to that of the velocity.The Karman vortex street generated by the patches on the same side would merge into a larger vortex street.Depending on its intensity,the vegetation at the back has different effects on the vortex street.展开更多
In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,...In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,and soil properties of livestock trampling routes and inter-route spaces in northern and southern facing hillslopes.Overall,both hillslope aspects were visually similar,whereas the ground surface of the routes was brighter(74.4%were characterized as having a'light'color)than the inter-route spaces(86.8%were characterized as having a'dark'color).These observations were supported by morphological identification of biocrust composition,which was dominated by cyanobacteria(67%)in the routes,and by mixed cyanobacteria/moss(56%)in the inter-routes.Mean Normalized Difference Vegetation Index(NDVI)was 24%higher in the inter-routes,while the mean Brightness Index(BI)was 12%higher in the routes.At the same time,the mean Crust Index(CI)was identical in the two microhabitats.Soil quality index(SQI),calculated based on the(pedoderm)soil properties of the two microhabitats,was 6%greater in the inter-routes than in the routes.This study suggests that recurrent trampling exacerbates soil compaction and shearing along the routes,thus preventing the successional development of complex biocrust compositions.展开更多
基金funded by the National Natural Science Foundation of China (41301298)the State Key Program of National Natural Science Foundation of China (41030532)the Special Fund of Strategic Priority Research Program of Chinese Academy of Sciences (XDA05060300)
文摘Vegetation patterns are important in the regulation of earth surface hydrological processes in arid and semi-arid areas. Laboratory-simulated rainfall experiments were used at the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling, northwestern China, to quantify the effects of Artemisia capillaris patterns on runoff and soil loss. The quantitative relationships between runoff/sediment yield and vegetation parameters were also thoroughly analyzed using the path analysis method for identifying the reduction mechanism of vegetation on soil erosion. A simulated rainfall intensity of 90 mm/h was applied on a control plot without vegetation （Co） and on the other three different vegetation distribution patterns： a checkerboard pattern （CP）, a banded pattern perpendicular to the slope direction （BP）, and a single long strip parallel to the slope direction （LP）. Each patterned plot received two sets of experiments, i.e. intact plants and roots only, respectively. All treatments had three replicates. The results showed that all the three other different patterns （CP, BP and LP） of A. capillaris could effectively reduce the runoff and sediment yield. Compared with Co, the other three intact plant plots had a 12%-25% less runoff and 58%-92% less sediment. Roots contributed more to sediment reduction （46%-70%）, whereas shoots contributed more to runoff reduction （57%-81%）. BP and CP exhibited preferable controlling effects on soil erosion compared with LP. Path analysis indicated that root length density and plant number were key parameters influencing runoff rate, while root surface area density and root weight density were central indicators affecting sediment rate. The results indicated that an appropriate increase of sowing density has practical significance in conserving soil and water.
基金supported by the Key Research and Development Program of Ningxia Hui Autonomous Region,China(2022BEG02003)the Excellent Member of Youth Innovation Promotion Association,Chinese Academy of Sciences(Y202085)the Youth Innovation Promotion Association,Chinese Academy of Sciences(2023448).
文摘The development of bare patches typically signifies a process of ecosystem degradation.Within the protection system of Shapotou section of the Baotou-Lanzhou railway,the extensive emergence of bare sand patches poses a threat to both stability and sustainability.However,there is limited knowledge regarding the morphology,dynamic changes,and ecological responses associated with these sand patches.Therefore,we analyzed the formation and development process of sand patches within the protection system and its effects on herbaceous vegetation growth and soil nutrients through field observation,survey,and indoor analysis methods.The results showed that sand patch development can be divided into three stages,i.e.,formation,expansion,and stabilization,which correspond to the initial,actively developing,and semi-fixed sand patches,respectively.The average dimensions of all sand patch erosional areas were found to be 7.72 m in length,3.91 m in width,and 0.32 m in depth.The actively developing sand patches were the largest,and the initial sand patches were the smallest.Throughout the stage of formation and expansion,the herbaceous community composition changed,and the plant density decreased by more than 50.95%.Moreover,the coverage and height of herbaceous plants decreased in the erosional area and slightly increased in the depositional lobe;and the fine particles and nutrients of soils in the erosional area and depositional lobe showed a decreasing trend.In the stabilization phases of sand patches,the area from the inlet to the bottom of sand patches becomes initially covered with crusts.Vegetation and 0-2 cm surface soil condition improved in the erosional area,but this improvement was not yet evident in the depositional lobe.Factors such as disturbance,climate change,and surface resistance to erosion exert notable influences on the formation and dynamics of sand patches.The results can provide evidence for the future treatment of sand patches and the management of the protection system of Shapotou section of the Baotou-Lanzhou railway.
基金This work was supported by the Beijing Natural Science Foundation[grant numbers 8181001 and 8132045]the Key Topics in Innovation Engineering of Chinese Academy of Sciences(CAS)[grant number Y225016EA2].
文摘Extremely hot environments can trigger serious health problems.To evaluate the effects of microclimate on thermal comfort,we proposed and validated a modified thermal humidity index(MTHI)that combined air temperature and relative humidity with land surface temperature(LST).MTHI was more sensitive to microclimate changes than the general thermal humidity index that includes only T and RH,and thus the thermal comfort could be better indicated.In an urban riparian buffer study,we estimated the temporal dynamics and spatial distribution of MTHI values for 47 vegetation patches and explored how structural characteristics of patches affect the thermal comfort.The results showed that planting could significantly reduce LST and MTHI.Vegetation patches with complex vertical structures had considerably higher thermal comfort than those with simple structures.Decreasing nearest distance to river or increasing plant abundance could reduce the thermal discomfort.There were significant differences in the structure characteristics between the patches with MTHI<70 and those with MTHI>70,implying the critical thresholds of variations in thermal comfort with patch structure.Given that people always feel uncomfortable during the daytime in July,optimizing the patch structure is essential to improve the microclimate regulation services of an urban landscape.
基金Projects supported by the National Natural Science Foundation of China(52022063,52179074 and U2040219).
文摘In natural rivers,patches of vegetation generally expand over their steady wake region in the streamwise direction,forming elongated patches with length(L)greater than their width(b).This paper studies how the wake flows and the vortices develop as the emergent patches expand their length in the streamwise direction.The patches are modeled with the same width but different lengths in laboratory experiments.Behind the patches,the steady wake region(L_(w))is not related to the width-related flow blockage(C_(d)ab),where C_(d) is the drag coefficient,a is the vegetation density.Instead,L_(w) is related to the length-related flow blockage(C_(d)aL).On this basis,a model is proposed for predicting L_(w),which is in good agreement with the measurements.As a patch becomes denser and/or longer(as C_(d)aL increases),the steady wake region becomes shorter(L_(w) decreases),and vortices are observed closer to the patch trailing edge,producing a turbulence of a greater magnitude beyond L_(w).When the flow blockage increases to the limit(C_(d)aL>8),the Karman vortices are observed directly behind the porous patches.These results can be used to explain the longitudinal elongation of the vegetation patches in the field.
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFC0407302)the National Natural Science Foundation of China(Grant Nos.51539007,51479128).
文摘The hydraulic characteristics in an open channel with vegetation are very important in controlling the environment pollution and restoring the river ecology. This paper studies the influence of the bed form and the vegetation patch density on the spatial velocity pattern. Rigid fiberglass circular cylinders are used to simulate the vegetation and a 3-D acoustic Doppler velocimeter (ADV) is used to measure the local flow velocities. Two types of bed forms and a series of vegetation patch densities are considered. The experimental results show that the bed form significantly influences the vertical distribution of the streamwise velocity. Besides, the velocity is affected by the bed form while the lateral distribution shape of the streamwise velocity as well as the lateral and longitudinal distribution shapes of the depth-averaged velocity is less affected. When all test conditions but the bed condition remain the same, as a result of the water energy consumption by the sediment movement, the velocity in the mobile bed case is smaller than that in the rigid bed case. The vegetation patch density has a significant effect on the flow velocity. The distributions of the flow velocity at different locations show different trends with the increase of the vegetation patch density. The upstream adjustment length is not affected by the vegetation patch density, but the steady wake length is very much affected.
基金supported by the National Natural Science Foundation of China(Grant Nos.51979181,51539007)。
文摘A staggered distribution of vegetation is very common in nature,which might significantly affect the flow structure.To investigate its impact,three rows of staggered vegetation groups are designed under seven different working conditions.The horizontal and vertical distances between the vegetation groups are constant,while the vegetation density is variable.The flow field is measured by the acoustic Doppler velocimeter(ADV).It is indicated that both the patch exit velocity and the steady wake velocity decrease with the increase of the density,which is also related to the vegetation rows.Except for the first patch,the upstream adjustment regions of all patches are diminished to some extent,due to the effect of the contralateral patch.The steady wake region also shows a decreasing trend,with a reduction of 0.5D each time when the water flows through the patch.This means that the flow structure is also affected by the number of vegetation rows.The intensity of the turbulence increases along the channel and has a non-axisymmetric distribution similar to that of the velocity.The Karman vortex street generated by the patches on the same side would merge into a larger vortex street.Depending on its intensity,the vegetation at the back has different effects on the vortex street.
文摘In drylands,biocrusts play crucial roles in regulating ecosystem functions.The study was conducted in the hilly rangelands of the semi-arid northern Negev of Israel,where we assessed the visual,morphological,spectral,and soil properties of livestock trampling routes and inter-route spaces in northern and southern facing hillslopes.Overall,both hillslope aspects were visually similar,whereas the ground surface of the routes was brighter(74.4%were characterized as having a'light'color)than the inter-route spaces(86.8%were characterized as having a'dark'color).These observations were supported by morphological identification of biocrust composition,which was dominated by cyanobacteria(67%)in the routes,and by mixed cyanobacteria/moss(56%)in the inter-routes.Mean Normalized Difference Vegetation Index(NDVI)was 24%higher in the inter-routes,while the mean Brightness Index(BI)was 12%higher in the routes.At the same time,the mean Crust Index(CI)was identical in the two microhabitats.Soil quality index(SQI),calculated based on the(pedoderm)soil properties of the two microhabitats,was 6%greater in the inter-routes than in the routes.This study suggests that recurrent trampling exacerbates soil compaction and shearing along the routes,thus preventing the successional development of complex biocrust compositions.
