Search

Dried soil layer (DSL) is a phenomenon of deep soil desiccation caused by soil water content (SWC) deficiency. Relevant studies in the fragmented terrain of Chinese Loess Plateau (CLP) remain limited. In a typical slope‐gully unit near the Liudaogou catchment, SWC was measured using neutron probes on 19 occasions at 15 observational locations. In order to reveal the temporal stability and elimination degree of DSLs, available soil moisture (ASM) and DSL were estimated by representative sites which were determined through the temporal stability method, and the reliability of simulating mean condition of the study area via representative locations was assessed. Results show that: (1) the dynamics of DSL was characterised by complexity and diversity. The ASM within the DSL (DSL‐ASM), ASM within the sandwiched DSL (SDSL‐ASM) and quantitative index (QI) varied within the range of 2.75%–3.11%, 2.98%–4.22% and 0.254–0.356, respectively. (2) The possibility of development and recovery for DSL and SDSL in deep layers were less than that in shallow layers. The maximum depth of DSL (DSLMD) was significantly and negatively related to the standard deviation of relative difference (SDRD) of DSL‐ASM, the maximum depth of SDSL (SDSLMD) was negatively related to the SDRD of SDSL‐ASM. (3) The prediction results of ASM above 300 cm depth were more accurate than other layers (R2 = 0.89). The DSL‐ASM had more accurate ability of prediction than SDSL‐ASM and QI. On the analysis of time stability characteristics of ASM and DSLs, the locations of A2 and C3 can better represent the mean conditions of ASM at three and four soil layers, respectively. C2, A1 and A1 can better represent the average levels of DSL‐ASM, SDSL‐ASM and QI, respectively (R2 = 0.43, 0.14 and 0.18). (4) The restoration degrees of DSLs mainly showed no elimination and slight elimination, the DSLs cannot be completely eliminated within a short time. We proposed that scientific regulation of SWC can alleviate the formation and development of DSLs at a certain extent, and provide the possibility for DSLs nonoccurrence. [ABSTRACT FROM AUTHOR]

Soil water storage (SWS) dynamics are affected by many factors in semiarid regions such as the Loess Plateau. Spatiotemporal variation of SWS varies greatly with different landscape positions due to the rolling and fragmented terrain landscape of the Loess Plateau. However, information on the SWS and its temporal stability at different landscape positions is lacking. In this study, hillslope, dam land and gully landscape positions were selected in a typical small watershed in the Loess Plateau. A soil water observation belt with 28 sample locations was set up at each landscape position, and temporal stability analysis was conducted using SWS data of 12 sampling events. The results showed that the variation characteristics of profile SWS are influenced by landscape position. The persistence of spatial SWS patterns in different landscape positions increases with the increase of soil depth. On each landscape position, representative locations can accurately predict their SWS based on temporal stability analysis. Moreover, the stability of SWS at the representative locations was more important than its content during the prediction process. The dominant factors that lead to the difference of temporal stability characteristics in different landscape positions varied with the change in soil depths. The results provide an important basis for vegetation reconstruction and water management in small Loess Plateau watersheds. [ABSTRACT FROM AUTHOR]

Understanding the spatio‐temporal variability of soil water content (SWC) in the Critical Zone (CZ) is essential to balance plant‐water benefits and to enhance the ability to monitor and predict drought. In current study, the spatial variability and temporal stability of multi‐layer SWC to a depth of 500 cm (35 soil layers) at 27 sampling sites were evaluated at a hillslope scale. A total of 64 SWC measurements were obtained from 28 March, 2017 to 23 December, 2018. We hypothesized the existence of a "special point" that is temporally stable both in horizontal direction (which means different layers) and in vertical direction (which means different profiles). We found a clear seasonal dynamic pattern of mean SWC for all sites in the 0–500 cm profile, with SWC varying from 4.0 to 24.8%. In the horizontal layer, both the 130‐cm and 140‐cm layers contained a maximum number of temporal stability sites (N = 4) which all located at H11, H13, H14 and H26. In the vertical profile, H19 was the most stable site, followed by H10 and H26, with 15, 10 and 6 stable layers, respectively. The decreasing order of SWC temporal stability was 200–500 cm, 0–500 cm and 0–200 cm, which means the temporal stability of SWC in 0–500 cm profile was more dependent on the 0–200 cm sub‐profile. At a three‐dimension scale, the most temporal stability layer and site was 180‐cm of H1 and H21 of 220‐cm, which confirmed our hypothesis. This study provides an accurate description of SWC spatio‐temporal variation at the hillslope scale, which is helpful for addressing eco‐hydrological models and water management issues in the Earth's CZs. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial–temporal variability of soil water content is critical for water management and restoration of vegetation in semi‐arid areas. Using the temporal stability method, we investigated soil water relations and spatial–temporal variability of volumetric soil water content (VSWC) in the grassland–shrubland–forest transect at a typical semi‐arid subalpine ecosystem in the Qilian Mountains, northwestern China. The VSWC was measured on 48 occasions to a depth of 70 cm at 50 locations along a 240‐m transect during the 2016–2017 growing seasons. Results revealed that temporal variability in VSWC in the same soil layer in the three vegetation types and averaged across vegetation types tended to exhibit similar patterns of a decrease with increasing soil depth. Temporal stability in each vegetation type was stronger with an increase in soil depth. However, the results of temporal stability determined with standard deviation of relative difference (SDRD) disagreed with those based on the Spearman's rank correlation coefficient; the forest site had the highest Spearman rank correlation coefficient while the shrubland—the smallest SDRD in the 0–20 cm soil layer. Correlation analyses of VSWCs between two vegetation types indicated that soil water was related among all three vegetation types at the 0–20, and 0–70 cm soil layer, but in the 20–40 and 40–70 cm soil layers, significant correlation (p <.01) occurred only between adjacent vegetation types. In the upper soil layer (0–20 cm), soil water relations were mainly affected by surface runoff. In the lower soil layer (20–40 and 40–70 cm), soil water relations among the three vegetation types were highly complex, and probably resulting from a combination of root distribution and activity, interflow, and the impact of deep soil freeze–thaw dynamics. These results suggest that the factors affecting soil water are complex, and further research should address the relative importance of and interactions among different determining factors. [ABSTRACT FROM AUTHOR]

Soil water content (SWC) is a key factor for successful vegetation restoration in arid and semiarid regions, and vegetation has significant influences on the spatial patterns and temporal dynamics of SWC. The aim of this study was to investigate the temporal stability of SWC under different restored grasslands in an arid hilly area of Central China. SWC was measured in the 0‐ to 300‐cm soil profile in the natural grassland (Stipa capillata) and three typical planted grasslands (Medicago sativa, Agropyron cristatum, and Caragana korshinskii) over two growing seasons (from June to October 2015 and 2016) under natural rainfall conditions. The results showed that the mean SWC in the natural grassland was approximately 30% higher than those in the planted grasslands. The SWC consumption of the planted legume grasslands in the deepest soil layers (below 200 cm) was higher than that of the natural grassland, owing to the deep root system of the legumes. Both natural and planted grasslands had low SWC temporal stability in the top soil layers (0–50 cm), whereas more stable conditions were gradually observed with increasing the soil depth. The mean value of the mean relative differences of SWC in natural grassland (ca. 15%) was lower than that in the planted grasslands (A. cristatum grasslands) and much lower than that in the scrubland, highlighting the stronger temporal stability of SWC in the natural grassland. In conclusion, natural grassland could maintain higher and stable SWC and is recommended to be used for achieving sustainable vegetation restoration in arid and semiarid regions. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic relationships among rainfall patterns, soil water distribution, and plant growth are crucial for sustainable conservation of soil and water resources in water‐limited ecosystems. Spatial and temporal variation in deep soil water content at a watershed scale have not yet been characterized adequately due to the lack of deep soil water data. Deep soil–water storage (SWS) up to a depth of 5 m (n = 73) was measured at 19 sampling occasions at the LaoYeManQu watershed on the Chinese Loess Plateau (CLP). At a depth of 0–1.5 m, the annual mean SWS was highly correlated with rain intensity, and the correlation decreased with depth, but within the layers at 1.5–5.0 m, the changes in SWS indicated a lag between precipitation and the replenishment of soil water. Geostatistical parameters of SWS were also highly dependent on depth, and the mean SWS presented similar spatial structures in two adjacent layers. Temporal stability of SWS as indicated by mean relative difference, standard deviation of the relative difference (SDRD), and mean absolute bias error (MABE) was significantly weaker at the shallow than at deeper layers. Soil separates and organic carbon content controlled the spatial pattern of SWS at the watershed scale. One representative location (Site 57) was identified to estimate the mean SWS in the 1‐ to 5‐m layer of the watershed. Semivariograms of the SDRD and MABE were best fitted by an isotropic spherical model, and their spatial distributions were depth‐dependent. Both temporal stability and spatial variability of SWS increased over depth. This study is helpful for deep SWS estimation and sustainable management of soil and water on the CLP, and for other similar regions around the world. [ABSTRACT FROM AUTHOR]

Temporal stability of soil moisture has been widely used in hydrological monitoring since it emerged. However, the spatial analysis of temporal stability at the landscape scale is often limited because of insufficient sampling numbers. This work made an effort to investigate the spatial variations of temporal stability of soil moisture in an oasis landscape. The specific objectives of the study were to explore the spatial patterns of temporal stability and to determine the controlling factors of temporal stability in the desert oasis. A time series of soil moisture measurements were gathered on 23 occasions at 118 locations over 3 years in a rectangular transect of approximately 100 km2. The nonparametric Spearman's rank correlation coefficient, standard deviation of relative difference (SDRD), and mean absolute bias error (MABE) were used to quantify the temporal stability of soil moisture. Results showed that the temporal stability of soil moisture was depth dependent and season dependent. The spatial pattern of soil moisture in a deep soil layer and between two same seasons generally had a high temporal stability. SDRD and MABE were spatially autocorrelated and exhibited strong spatial structures in the geographic space. The concept of temporal stability can be extended to describe the time-stable areas of soil moisture with geostatistics. There were great differences between SDRD and MABE in describing the temporal stability of soil moisture and in identifying the controlling factors of temporal stability. In this case, MABE was a better alternative to estimate the areal mean soil moisture using representative locations than SDRD. Land use type, soil moisture condition, and soil particle composition were the dominant controls of temporal stability in the oasis. These insights could help to better understand the essence of temporal stability of soil moisture in arid regions. [ABSTRACT FROM AUTHOR]

We examined the effect of strip thinning on the spatio-temporal variability of throughfall (TF) in a mature Japanese cypress (Chamaecyparis obtusa) stand. Strip thinning, which removed 50% of stems, was performed in a catchment in October 2011. TF was examined by setting up 20 tipping-bucket rain gauges in an experimental plot. Canopy interception parameters were derived from high-temporal-resolution TF data. Observations were obtained during the growing season in the pre-thinning and postthinning periods. The results demonstrated that after thinning, the TF rate increased from 64.3 to 76.2%, and the mean coefficient of variation of the TF rate significantly decreased from 27.3 ± 9.7 to 22.5 ± 6.8%. The spatial TF patterns were largely related to the rainfall class. There was no significant difference in the TF rate for the rainfall amount >25mm between the periods. The temporal persistence of the normalized TF was slightly stable in the post-thinning period and was not significantly related to canopy cover or the distance to the nearest trunk of each rain gauge in either period. Additionally, thinning resulted in an increase in the proportion of direct TF (from 0.14 ± 0.07 to 0.33 ± 0.11) and a decrease in canopy water storage (from 2.4 ± 0.7 to 1.5 ± 0.5 mm). The quantification of the canopy interception parameters can aid in modelling the changes in interception loss and its processes induced by thinning. These findings also help recognize the changes in spatial TF patterns under different forest management practices. [ABSTRACT FROM AUTHOR]

From May to October 2010, throughfall associated with 38 rainfall events in three below-canopy zones (inner canopy, mid-canopy and canopy periphery) of nine juvenile lodgepole pine trees and in open areas between canopies was measured along north, south, east and west transects radiating from each tree bole. Median cumulative throughfall (%) significantly differed among the canopy zones under differing rain depth classes and was negatively correlated with tree size metrics, but only for certain combinations of canopy zones and rain depth classes. Although median cumulative throughfall (%) was negatively correlated with canopy cover fraction when all below-canopy gauges were considered, this relationship only held true for the inner-canopy and mid-canopy zones under relatively small rain depth classes. Additionally, cumulative throughfall (%) was often dependent on transect direction, with event throughfall showing a dependence on the direction of storm origin. Throughfall coefficient of variation (%) also varied by zone and was a function of not only rainfall depth but also other storm variables such as the maximum 30-min rainfall intensity and the number and duration of intra-storm breaks. Temporal persistence of throughfall was assessed using time stability plots and Spearman rank coefficients of rain event and depth class pairings for all gauges and by canopy zone, and the influence of temporal lag and meteorological variables on persistence was assessed. The implications of our findings on throughfall sampling and for future ecohydrological studies in juvenile lodgepole pine and similar stands are discussed. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Temporal stability of soil water content (TS SWC) is an often-observed phenomenon, which characterization finds multiple applications. Climate and variability in soil properties are usually mentioned as factors of TS SWC, but their effects are far from clear. The objective of this work was to use SWC modeling to evaluate the effects of climate and soil hydraulic properties on the TS of soil water at different measurement schedules. We selected four representative climates found in USA and simulated the multiyear SWC dynamics for sandy loam, loam, and silty clay loam soils, all having the lognormal spatial distribution of the saturated hydraulic conductivity. The CLIMGEN and the HYDRUS6 codes were used to generate weather patterns and to simulate SWC, respectively. Four different methods were applied to select the representative location (RL). The low probability of having the same variability of mean relative differences of soil water under different climates was found in most of the cases. The probability that the variance of mean relative differences depended on sampling frequency was generally higher than 91% for the three soils. The interannual difference in mean relative differences variation from short and intensive summer campaigns was highly probable for all climates and soils. The RLs changed as climate and measurement scheduling changed, and they were less pronounced for coarse-textured soils. The RL selection methods based solely on bias provided more consistency as compared with other methods. The TS appears to be the result of the interplay between climate, soil properties, and survey protocols. One implication of this factor interaction effect on TS SWC is that a simulation study can be useful to decide on the feasibility of including a search for TS-based RLs for a specific site. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Spatio-temporal patterns of throughfall (TF) have often been studied under forest canopies. Few reports, however, have been made on small-scale TF variability in deciduous forest stands. In the present research, the spatial heterogeneity and temporal stability of TF under five individual persian oak trees ( Quercus brantii var. Persica) was quantified. The research site was in the Zagros forests in western Iran, where mean annual precipitation and temperature are equal to 587.2 mm and 16.9 °C, respectively. Data from 23 rainfall events were aggregated to assess the spatial correlation of TF. Variograms for TF beneath two of the five trees reached a stable sill at the range of 5-6 m. The redistribution of TF within the canopy was highly variable in time, attributable to seasonal variation in canopy foliation and meteorological factors. As the length of the sampling period increased, the spatial variability of TF decreased and the temporal stability of the TF pattern increased. Time stability plots of TF normalized with respect to mean and variance showed a moderate general persistence for all individual trees. We conclude that single trees modify the spatial distribution of TF reaching the forest floors. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Throughfall has been widely studied in forests but there is a scarcity of studies that focus on the spatial variability and temporal stability of throughfall in eucalyptus plantations. We examined throughfall in a daily basis in a 2·5-year eucalyptus plantation in southeastern Brazil using three sample arrangements: (1) close to tree trunks (CT) and in the central point between trunks (BT), (2) four-radial layout centred in tree trunk and (3) eight-radial layout. Throughfall was spatially non-uniform and varied according to the spatial monitoring arrangement: accumulated throughfall/precipitation ratio of 146% (CT) and 85% (BT) in arrangement 1, mean throughfall of 88% in arrangement 2, 84% (hilltop) and 85% (side slope) in arrangement 3. The highest throughfall values, spatial variability and persistence of dry and wet conditions were found close to eucalyptus trunks. Often accumulated throughfall close to trunks exceeded rainfall, especially for long-duration rainfall > 5 mm. The 'funnel effect' was consistently observed in all three arrangements and we speculate that the high throughfall concentration and temporal stability are related to canopy structures of eucalyptus. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The antecedent soil moisture status of a catchment is an important factor in hydrological modelling. Traditional Hortonian infiltration models assume that the initial moisture content is constant across thewhole catchment, despite the fact that even in small catchments antecedent soil moisture exhibits tremendous spatial heterogeneity. Spatial patterns of soil water distribution across three transects (two ina burnt area and one in an unburnt area) in a semi-arid area were studied. At the transect scale, when the factors affecting soil moisture were limited to topographical position or local topography, spatialpatterns showed time stability, but when other factors, such as vegetation, were taken into account, the spatial patterns became time unstable. At the point scale, and in the same areas, topographical position was the main factor controlling time stability. Scale dependence of time stability was studied and local topography and vegetation presence were observed to play an important role for the correlation between consecutive measures depending on the scale. [ABSTRACT FROM AUTHOR]