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Biochar is an eco-friendly material that is potentially used in earthworks to prevent stability and serviceability problems under extreme scenarios. This study aims to examine the effects of biochar amended on water infiltration and evaporation under extreme climate. A series of numerical analyzes were conducted to observe the response of pore water pressure (PWP) to extreme climate variation with an application of biochar composition. Moreover, an analysis of variance (ANOVA) has been performed to investigate the effect of biochar on soil water holding capacity at a low suction range. According to the result, biochar amended can maintain the fluctuation of PWP due to wetting and drying processes under extreme climate scenarios. This is due to the fact that the finer particles of biochar may clog large soil pores, reducing the water infiltration rate. Moreover, the addition of biochar can increase water retention capacity at low matric suction ranges, which can prevent flooding during extreme wet conditions. Further to this, the addition of biochar to the soil can maintain PWP fluctuation at the near surface area under extreme climate, preventing soil desiccation cracks. [ABSTRACT FROM AUTHOR]

Amidst intensifying global agricultural water demand, optimizing management practices and understanding the role of soil amendments, particularly biochar (BC), in modulating soil water dynamics are critical. Here, we review the potential impacts of BC on soil water dynamics, elucidate mechanistic underpinnings, and identify critical research gaps and prospective avenues. In general, BC modifies soil structure, hydraulic properties, surface albedo, and heat fluxes, which influence soil water storage, energy balance, and irrigation paradigms. Depending on soil texture and BC properties, BC demonstrates a greater reduction in bulk density and saturated hydraulic conductivity in coarse-textured soils compared to fine-textured soils. BC application generally increases water holding capacity (WHC) while exhibiting no consistent impact on soil water infiltration. Increased WHC of soils results from increased porosity, surface area, and soil aggregation. Increased porosity arises from a confluence of factors, encompassing new pores formation, reorganization of pores, increased soil aggregation, dilution effects of BC, reduced soil compaction, and biotic interactions, including increased population of burrowing invertebrates. BC tends to increase plant-available water in coarser soils, attributed to its hydrophilic nature, augmented specific surface area, and enhanced overall porosity. However, BC may induce soil water repellency, contingent upon variables such as feedstock composition, pyrolysis temperature, and specific soil attributes. While BC exhibits transformative potential in enhancing soil hydraulic properties, scalability concerns and economic viability pose challenges to its widespread agricultural application. Overall, BC offers promising avenues for sustainable water management. However, it is imperative to explore large-scale applications and conduct long-term field studies across different management, climate, and soil types to fully understand how different types of BC impact soil water dynamics. Highlights: Biochar generally improves soil water retention in coarse-textured soils. In coarse-textured soils, biochar increases porosity and PAW but decreases bulk density and Ksat. The effects of biochar on infiltration rates vary depending on soil types, as well as biochar particle size, production temperature, and depth of placement. Further studies on the mechanisms governing water retention in biochar-amended soils are warranted. Long-term studies encompassing various soil and biochar types are necessary. [ABSTRACT FROM AUTHOR]

Purpose: Elucidating the effects of vegetation on soil mechanical and hydrological behavior is crucial to understand shallow landslide stability. However, in geohazard-prone regions, quantifying the soil hydrological behavior is challenging because of large variations in soil water. The positive effects of vegetation hydrological effects have not been clearly delineated. The objective of this study was to analyze the contribution of vegetation types to slope stability under different soil matric suction conditions. Methods: The hydrological and mechanical properties of soil were measured and the extended Mohr–Coulomb failure criterion were used to estimate the differences in hydrological reinforcement on slopes under three vegetation types (grasslands, trees, and shrubs). The slope stability was compared using a two-dimensional finite element model. Results: The results showed that the increase in soil hydrological reinforcement of grasslands (16%) was higher than that of shrubs (13%) and trees (9%). The displacement vector and plastic strain cloud map indicated that slope failure was initiated from the foot of the slope; additionally, the plastic strain area of the grasslands was considerably larger than that of the shrubs and trees. Furthermore, with increase in matric suction, the factor of safety (FoS) of slope for trees, shrubs, and grasslands increased from 1.87 to 2.87, 1.50 to 3.53, and 1.47 to 3.32, respectively, with minimum variations in the FoS of slope for trees. Conclusions: This study provides valuable insights for quantifying the contribution of soil matric suction to the hydrological reinforcement of shallow slopes under different vegetation types. To maintain slope stability, understanding the soil hydrological properties is important to select suitable plants that can strengthen slope stabilities, allocate plant communities scientifically and rationally, and guide the implementation of appropriate land management practices. [ABSTRACT FROM AUTHOR]

The rock fragment (RF) has been widely observed in the soil solum or on the soil surface. It regulates soil hydrological processes (SHPs) and thus has great impacts on soil and water conservation. However, responses of SHPs to RF characteristics (position, content, coverage area, mulching thickness, and size) remain unclear. Based on the dataset extracted from 168 published studies, effects of RF characteristics on SHPs (soil loss rate, evaporation rate, surface runoff rate, infiltration rate, soil water content, and soil water storage) and saturated hydraulic conductivity (Ks) were discussed in this study. Results showed that RFs completely inserted into the soil solum (CO_INS) improved the Ks by 6.9%, runoff rate by 12.8%, and soil loss rate by 22.3%, while it reduced the evaporation rate by 30.7%, infiltration rate by 15.4%, and soil water content by 9.9%. With the RF content (kg kg−1) increasing, its effects on these SHPs were strengthened. The RFs resting on the surface and partially covering soil surface (PA_COV) improved the infiltration rate but reduced the evaporation rate by 36.9%, surface runoff rate by 25.4%, and soil loss rate by 59.3%. This in turn enhanced soil water content and storage. However, as the RF coverage (% in area) increasing, the cross-sectional area of water flow decreased, and thus the infiltration rate reduced. The RFs completely mulch on the soil surface (CO_MUL) reduced the evaporation rate by 59.5% and infiltration rate by 76.5% but improved the soil water content and storage. Except the infiltration rate, the effects of CO_MUL on SHPs were strengthened as mulch thickness (cm) increased. The RFs partially embedded into soil surface (PA_EMB) promoted surface runoff rate by 15.3%, soil loss rate by 34.7%, and soil water content by 24.3%, but reduce the infiltration rate. However, the surface runoff rate was reduced at high embedded coverage due to increased tortuosity of water flow. In addition, the RF size exerted weaker effects on SHPs than RF positions, content, coverage, and mulch thickness. Our findings enhanced the understanding of SHP responses to RFs characteristics, which would be important for relate soil and water modeling and management. [ABSTRACT FROM AUTHOR]

The soil freeze–thaw process is a transition phase of soil water in cold areas that influences the soil's hydrological behavior. However, dynamic phenomena and corresponding consequences have yet to be studied adequately. Therefore, the present study was planned to comparatively analyze the effects of a freezing–thawing cycle on the hydrologic behaviors of loess soil from northeast Iran. Small-size (0.5 × 0.50 m) erosion plots were subjected to a freezing–thawing cycle under governing conditions of the region of the origin soil. The plots were subjected to a freezing–thawing treatment by inducing cold air until the temperature declined to below − 20 °C and lasted for 3 days using a cooling compartment system and then were kept in the laboratory with an ambient temperature of above 10 °C for 2 days. The treated plots and untreated plots were then exposed to a simulated rainfall with an intensity of 72 mm h−1 and 0.5 h duration while they were placed on a slope of 20%. The results indicated that the hybrid processes of freezing–thawing and splash and inter-rill erosions significantly increased runoff generation and soil loss. The time to runoff, runoff volume, and soil loss were 1.65 times less and 1.38 and 2.90 times more, respectively, compared to those reported for the control treatment with significant differences (p < 0.006). The performance of ice lenses, freezing fronts, and the creation of near-saturation moisture after completing the cycle were identified as the most critical factors affecting the different soil behaviors under the frozen-thawed cycle. [ABSTRACT FROM AUTHOR]

Gypsum (CaSO4∙2H2O) amendment can reduce phosphorus (P) export from agricultural fields and protect water quality. Past studies have examined the impact of gypsum application rate, but limited research has been conducted to assess the effect of the time interval between gypsum application and P fertilization on treatment effectiveness and P mobility. To address this question, a mesocosm-scale experiment was conducted using 36 soil columns packed with either Brookston clay-loam (total phosphorus, TP: 0.46 g kg−1) or Fincastle silt-loam soil (TP: 4.63 g kg−1). For each soil type, 9 columns were treated with gypsum (5 Mg ha−1) and an equal number served as untreated controls. At different time intervals (2, 30, and 58 days after gypsum application), one-third of the columns received P fertilizer (34 kg P ha−1). Rainwater was added to generate leachate that was collected over a 3-week period and analyzed for pH, sulfate (SO4−2), dissolved reactive P (DRP), and TP. At the end of each leaching period, soil columns were sliced (2–5 cm layers), and the amount of water-extractable P (WEP) and Olsen-P was quantified. The gypsum treatment had generally no effect on Olsen-P, but it consistently resulted in lower WEP level (1.8-fold) compared to controls. Likewise, during the later stage of the experiment (> 30 days), the gypsum treatment resulted in DRP concentration reduction (28–52%) in leachate from the Fincastle soil columns (but the effect was marginal in the Brookston columns likely due to limited distribution of surface applied gypsum in this fine-textured soil). These results indicated that the effect of gypsum on DRP leaching varies with the timing of P application. Depending on soil type, an interval of 1–2 months (shorter interval for coarse-textured soils; longer interval if soils are fine-textured) should be adopted before applying P fertilizer in order to optimize the effectiveness of the gypsum treatment. [ABSTRACT FROM AUTHOR]

Purpose: Inconsistent controlling factors of soil water content (SWC) spatial variation across regions and spatial scales have been acknowledged in previous studies. However, universal principles explaining these inconsistencies are still needed to be explored. The main aim of this study was to conclude the universal principles across regions and scales. Materials and methods: In this study, based on the surface (< 10-cm soil depth) SWC dataset from Meng et al. (2021) (https://doi.org/10.5194/essd-13-3239-2021) and the relevant environmental variables (climate including temperature and precipitation, topography including elevation and slope, soil including sand and clay contents, and vegetation including normalized difference vegetation index or NDVI) in a 1500 km × 1500 km study region in China, we calculated the correlations between them, and identified the controlling factors of surface SWC in different subregions and at different spatial scales. Results and discussion: Local factors like temperature, precipitation, and clay content that controling the vertical soil water replenishment and removal dominated the surface SWC spatial variation in this dry study region (mean SWC ≤ 0.10 m3 m−3). Nonlocal factors like topography (e.g., elevation and slope) and soil porosity (sand content) determining the lateral soil water redistribution had outweighed effects in the representative wet subregion. In addition, topography also exerted considerable effects on SWC in this study region due to its great spatial variability, especially when spatial scale < 800 km. As NDVI was complicatedly controlled by other environmental variables, its effect on SWC performed dramatic regional differentiation. In contrast, effect of slope on SWC was more associated with its spatial variability as it was independent from other environmental variables. Conclusions: This study emphasized that the inconsistencies of controlling factors of SWC spatial variation can be comprehensively explained by different regimes in the dry and wet conditions, spatial variability of environmental variables and the interactions among different environmental variables. These findings can deepen our understanding of the controls on SWC spatial variation across regions and scales. [ABSTRACT FROM AUTHOR]

We determined the soil properties and infiltration rates in 11 plots, including four soil types (Leptosol, Cambisol, Umbrisol and Regosol, according to the FAO criteria), under three different land uses (pine forest, oak forest and scrubland). The study was conducted in a Spanish Central System Mountain under a Mediterranean climate. We tried to quantify the effect of land use (native and reforested forest and scrubland) and soil properties on the steady-state soil infiltration rate because of the limited evidence about soil infiltration in Mediterranean mountains with sandy and acid soils developed on granite rocks. We employed a simple-ring methacrylate infiltrometer method to determine soil infiltration rates. We used correlation and principal component analysis to examine the relationships between soil properties, land uses, and water infiltration. Additionally, a one-way ANOVA model was applied to identify differences between vegetation types. Soil infiltration rates in the pine forest (891.9 mm·h−1) and the oak forest (509.0 mm·h−1) were better than those in the scrubland (178.4 mm·h−1). Our results are in agree with the main results in the scientific literature. Factors such as sand content (R = 0.71, p-value = 0.02) or electrical conductivity (salt content indicator; R = 0.81, p-value = 0.00) were positively related to soil infiltration, while clay was negatively related (R = −0.69, p-value = 0.02). Results show forest cover improves soil infiltration. This effect is strongly related to hydrological ecosystem services, which may be of interest for decision-making in natural environment management, especially for soil and water conservation. [ABSTRACT FROM AUTHOR]

The effects of a thinning treatment on soil respiration (Rs) were analysed in two dryland forest types with a Mediterranean climate in east Spain: a dry subhumid holm oak forest (Quercus ilex subsp. ballota) in La Hunde; a semiarid postfire regenerated Aleppo pine (Pinus halepensis) forest in Sierra Calderona. Two twin plots were established at each site: one was thinned and the other was the control. Rs, soil humidity and temperature were measured regularly in the field at nine points per plot distributed into three blocks along the slope for 3 years at HU and for 2 years at CA after forest treatment. Soil heterotrophic activity was measured in laboratory on soil samples obtained bimonthly from December 2012 to June 2013 at the HU site. Seasonal Rs distribution gave low values in winter, began to increase in spring before lowering as soil dried in summer. This scenario indicates that with a semiarid climate, soil respiration is controlled by both soil humidity and soil temperature. Throughout the study period, the mean Rs value in the HU C plot was 13% higher than at HU T, and was 26% higher at CA C than the corresponding CA T plot value, being the differences significantly higher in control plots during active growing periods. Soil microclimatic variables explain the biggest proportion of variability for Rs: soil temperature explained 24.1% of total variability for Rs in the dry subhumid forest; soil humidity accounted for 24.6% of total variability for Rs in the semiarid forest. As Mediterranean climates are characterised by wide interannual variability, Rs showed considerable variability over the years, which can mask the effect caused by thinning treatment. [ABSTRACT FROM AUTHOR]

Infiltration, as a major component of the hydrological cycle, plays an important role in ecosystems, river flooding, and soil erosion. Therefore, this process has been studied on different soils, with different vegetation cover, and under different climate conditions. However, it is still necessary to know how infiltration rates depend on land degradation, vegetation cover, forest management, and forest restoration, since soil infiltration is related to soil hydrological function and hydrological ecosystem services. The aim of our study is to analyze the way reforestation and check dam construction have helped to improve soil infiltration rates in comparison with old, degraded land, different soils and vegetation covers in Central Spain. Therefore, three infiltration tests were carried out by means of a simple methacrylate infiltrometer ring, in four sampling plots, for five types of land use: (i) native holm oak forest, (ii) 60-year-old reforested pine wood, (iii) shrubs, (iv) sediment wedges of check dams, and (v) gullies and degraded hillslopes. Our results show much higher infiltration rates in the soil of 60-year-old pine reforestation sites (1198.00 mm·h−1), and in the sediment wedges of check dams (1088.00 mm·h−1), than in those of degraded hillslopes (365.00 mm·h−1) and shrubland (420.80 mm·h−1). The rates were also shown to be close to those from the remaining patches of native holm oak woodland (770.40 mm·h−1). We also found that organic matter, humus and litter depth, and height of vegetation and cover, all improve soil infiltration rates, while slope degree, presence of coarse elements, stoniness, clay content, bulk density, and electric conductivity inhibit the rates. It was additionally seen that pine reforestation and check dam construction caused degraded land to recover its hydrological conditions to a level that is quite close to that of the ancient oak holm native forest, alongside ameliorating the hydrological cycle in the watershed. This information will be very useful for decision-making processes related to land restoration projects, forest management, and environmental policy. [ABSTRACT FROM AUTHOR]

The critical zone (CZ) represents the intersection of the biosphere with the atmosphere, hydrosphere and lithosphere. Understanding the hydrological processes and human impact factors on the CZ is fundamental to sustainable water resources management for agroforestry. Transpiration (T) is an important component of terrestrial evapotranspiration (ET), and understanding the time lag (TL) between vegetation transpiration and meteorological factors can improve our knowledge of the mechanisms of vegetation adaptability to a changing environment. However, the controlling factors on the TL remain poorly understood. Therefore, the objective of this study is identifying the temporal dynamics of key controlling factors on the TL, using a typical deciduous broad-leaved tree species (Zenia insigins Chun) of CZ in subtropical humid karst regions. This species is used as an example to explore the characteristics of the TL between SF (sap flow) and hydro-meteorological forcing. Sap flow in these 6 trees was monitored using the thermal dissipation probes (TDP). Results showed that: (1) the peak of diurnal sap flow generally lagged behind PAR but preceded Ta (air temperature), RH (relative humidity) and VPD (vapor pressure deficit), with the mean TL of −67.4 min (PAR), 90.5 min (Ta), 91.6 min (RH) and 92.9 min (VPD), respectively; (2) TL had no significant relationships with the daily mean meteorological factors and soil moisture, but was highly (R2>0.66) correlated to CRs (changing rates of meteorological factors) in the morning; (3) At seasonal scale, the sap flow rate and TL both were controlled by the seasonality of precipitation and temperature. Overall, the seasonality of the TL was caused by plants' high water loss and strongly active physiological response in hot seasons, leading to close stomata earlier than in cold seasons; (4) The reason why CRs proposed can explain the TL better than mean values of metrological factors is that the CRs considered the distribution and change processes of metrological factors in the daytime. This study may be helpful for understanding the physiological response of vegetation to climatic change, and may be useful for constructing models to simulate transpiration processes more accurately during a day. [ABSTRACT FROM AUTHOR]

Aims: To investigate the physiological responses of groundnut (Arachis hypogea) and pearl millet (Penisetum glaucum) that were intercropped with the native evergreen woody shrubs Piliostigma reticulatum (D.C.) Hochst and Guiera senegalensis J.F. Gmel compared to control crops throughout two growing seasons at two sites with contrasting climate and soil types in Senegal.Methods: Shrubs grown in groundnut and millet fields at higher than native density were coppiced annually with aboveground biomass returned to the soil and no additional fertilizer. Crop leaf area index (LAI), handheld normalized difference vegetation index (NDVI), leaf water potential, and soil moisture and temperature were monitored in 2012-2013.Results: At the drier site, the presence of shrubs reduced soil temperature at 5 cm depth by up to 5 °C during early crop growth. Shrub presence increased LAI by up to 266%, NDVI by up to 217% and increased groundnut leaf water potential throughout the day at the wetter site. Shrub effects on crop physiology were stronger overall at the drier site.Conclusions: These results improve the understanding of how this unique agroforestry system alters the growing environment and the physiological response of associated crops throughout the season. [ABSTRACT FROM AUTHOR]

Water regime of arable chernozems was simulated for two plots at the Voronezh experimental station. The first plot is under continuous corn monoculture since 1966. The second plot is under permanent bare fallow since the same time. The free HYDRUS-1D software was used. Evaporation from bare soil surface and evapotranspiration from the plot under corn were estimated using the FAO56 method. Simulations were performed for the 2013 and 2014 growing seasons with contrasting precipitation. Precipitation sum in May–September 2013 was 427 mm, and it was only 195 mm in May–September 2014, whereas the long-term average precipitation sum from May 1 to September 30 is equal to 284 mm. The monthly precipitation in July 2014 was only 2 mm. During both growing seasons, the simulated water regimes at the two plots were different. In the 70–140 cm layer, the soil water content was no less than 0.25 cm3/cm3 under bare fallow and it decreased to 0.17 cm3/cm3 under corn. The driest layers were formed under corn at the depths from 70 to 120 cm. At the plot under bare fallow, the cumulative evaporation from the soil surface from May 1 to September 30 in 2014 was higher than the precipitation sum for the same period. At the plot under corn, the cumulative evaporation was less than the precipitation sum, and the lower soil water content at this plot is explained by root water uptake with the cumulative value of 23 cm for the period from May 1 to September 30. [ABSTRACT FROM AUTHOR]

Hysteresis of the soil water retention curve (SWRC), manifested as a difference between equilibrium curves of soil wetting and drying (hysteresis loop), is a phenomenon specific to soil hydrology, which is of practical importance for calculating irrigation norms. We have attempted to derive a model of the wetting curve from the drying curve. Modeling was based on parameters proposed by van Genuchten [6] and certain soil physical characteristics. SWRC hysteresis characteristics were obtained experimentally using capillarimetric measurements for wetting and drying curves at soil water pressures ranging from 0 to -800 cmH2O. Two models, М-1 and М-2, based on the hypothesis of dissimilarity of parameters α for wetting (αw) and drying (αd) and the constancy of other parameters of the van Genuchten SWRC approximation for both curves of the hysteresis loop, have been developed for wetting curve assessment based on the drying curve. The M-1 error (RMSE = 0.05 cm-1) was less than that of M-2 (RMSE = 0.06 cm-1), which used clay content and soil density as predictors, as well as that of the well-known model proposed by Kool and Parker [11]. This approach to derive the wetting curve from the drying curve for a presumed correlation between the values of one parameter and equal values of the other parameters, can be used to predict an estimate of the SWRC hysteresis for a specific soil. [ABSTRACT FROM AUTHOR]

Most studies of greenhouse gas fluxes from forest soils in the coastal rainforest have considered carbon dioxide (CO), whereas methane (CH) has not received the same attention. Soil hydrology is a key driver of CH dynamics in ecosystems, but the impact on the function and distribution of the underlying microbial communities involved in CH cycling and the resultant net CH exchange is not well understood at this scale. We studied the growing season variations of in situ CH fluxes, microbial gene abundances of methanotrophs (CH oxidizers) and methanogens (CH producers), soil hydrology, and nutrient availability in three typical forest types across a soil moisture gradient. CH displayed a spatial variability changing from a net uptake in the upland soils (3.9-46 µmol CH m h) to a net emission in the wetter soils (0-90 μmol CH m h). Seasonal variations of CH fluxes were related to soil hydrology in both upland and wet soils. Thus, in the upland soils, uptake rates increased with the decreasing soil moisture, whereas CH emission was inversely related to the water table depth in the wet soils. Spatial variability of CH exchange was related to the abundance of genes involved in CH oxidation and production, but there was no indication of a temporal link between microbial groups and CH exchange. Our data show that the abundances of genes involved in CH oxidation and production are strongly influenced by soil moisture and each other and grouped by the upland-wetland classification but not forest type. [ABSTRACT FROM AUTHOR]

Purpose: Urban soils' variability in the vertical direction presumably affects hydrological parameters at the timescale. Moreover, horizontal soil alterations at small spatial scales are common in urban areas. This spatio-temporal variability and heterogeneity of soil moisture and the possible influencing factors were to be described and quantified, using data of a soil monitoring network in the city of Hamburg, Germany. Materials and methods: Soil moisture data from ten observation sites within the project HUSCO was evaluated for two different years. The sites were located within districts with different mean groundwater table depths and characteristic urban soil properties. Soil hydrological simulations with SWAP were calculated for a selected site. Results and discussion: The temporal evolution of soil water content and tension for the sites was very distinct, related to soil substrate, organic matter content, and groundwater table depth. Impacts of different vegetation rooting depths, the soil substrates' type, and to some extent the degree of disturbance on soil water dynamics could be identified. An impact of groundwater table depth on the water content of the topsoil during low-precipitation periods could be assumed. The comparison of the results of soil hydrological simulations with empirical data indicated an overestimation of infiltration and percolation for the given soil substrates. Conclusions: While soil properties are mainly determinant for the long-term progression of soil hydrology, local site factors affect the short-term regime. A shallow groundwater table contributes to more constant water dynamics while the relative decrease of water during a dry phase is diminished. [ABSTRACT FROM AUTHOR]

The hydrologic regimes of arable chernozems were simulated for two plots located within a watershed. For the last fifty years continuous corn monoculture was practiced in one plot, and permanent bare fallow was practiced in the other plot. Carbonates are detected from a depth of 140-160 cm under corn and from 70-80 cm under bare fallow. The objective of the simulation study was to test the validity of the hypothesis that the shallower depth to carbonates under bare fallow is related to carbonate rise due to changes in the hydrologic regime of bare soil compared to soil under vegetation. Mathematical modeling using the HYDRUS-1D software and the FAO56 method confirmed that the hydrologic regimes of arable chernozems within the two plots are different. The soil water content under bare fallow is generally higher than that under corn. The downward soil water fluxes for the two plots are comparable. The upward soil water fluxes under bare fallow significantly exceed those under corn and affect a thicker soil layer. The changes in the hydrologic regimes of chernozems under bare fallow favor the upward movement of carbonates through both the direct transfer by upward water fluxes and the diffusion of ions. [ABSTRACT FROM AUTHOR]

Soil moisture and its spatial pattern are important for understanding various hydrological, pedological, ecological and agricultural processes. In this study, data of rainfall and soil moisture contents at different depths (10 cm, 20 cm, 40 cm and 60 cm) in forestland and vegetable plot in the Taihu Lake Basin, China were monitored and analyzed for characteristics of soil moisture variation and its response to several typical rainfall events. The following results were observed. First, great temporal variation of soil moisture was observed in the surface layer than in deeper layer in vegetable plot. In contrast, in forestland, soil moisture had similar variation pattern at different depths. Second, initial soil moisture was an important factor influencing the vertical movement of soil water during rainfall events. In vegetable plot, simultaneous response of soil moisture to rainfall was observed at 10- and 20-cm depths due to fast infiltration when initial soil was relatively dry. However, traditional downward response order occurred when initial soil was relatively wet. Third, critical soil horizon interface was an active zone of soil water accumulation and lateral movement. A less permeable W-B soil horizon interface (40-cm depth) in vegetable plot can create perched water table above it and elevate the soil water content at the corresponding depth. Fourth, the land cover was an effective control factor of soil moisture during small and moderate rainfall events. In the forestland, moderate and small rainfall events had tiny influences on soil moisture due to canopy and surface O horizon interception. Fifth, preferential flow and lateral subsurface interflow were important paths of soil water movement. During large and long duration rainfall events, lateral subsurface flow and preferential flow through surface crack or soil pipe occurred, which recharged the deep soil. However, in more concentrated large storm, surface crack or soil pipe connected by soil macropores was the main contributor to the occurrence of preferential flow. Findings of this study provide a theoretical foundation for sustainable water and fertilizer management and land use planning in the Taihu Lake Basin. [ABSTRACT FROM AUTHOR]

An examination of the relation between runoff rate, R, and concentration, C, of twelve major constituents in four small watersheds in eastern Puerto Rico demonstrates a consistent pattern of responses. For solutes that are not substantially bioactive (alkalinity, silica, calcium, magnesium, sodium, and chloride), the log( R)-log( C) relation is almost linear and can be described as a weighted average of two sources, bedrock weathering and atmospheric deposition. The slope of the relation for each solute depends on the respective source contributions to the total river load. If a solute were strictly derived from bedrock weathering, the slope would be −0.3 to −0.4, whereas if strictly derived from atmospheric deposition, the slope would be approximately −0.1. The bioactive constituents (dissolved organic carbon, nitrate, sulfate, and potassium), which are recycled by plants and concentrated in shallow soil, demonstrate nearly flat or downward-arched log( R)-log( C) relations. The peak of the arch represents a transition from dominantly soil-matrix flow to near-surface macropore flow, and finally to overland flow. At highest observed R (80 to >90 mm/h), essentially all reactive surfaces have become wetted, and the input rate of C becomes independent of R (log( R)-log( C) slope of -1). The highest R are tenfold greater than any previous study. Slight clockwise hysteresis for many solutes in the rivers with riparian zones or substantial hyporheic flows indicates that these settings may act as mixing end-members. Particulate constituents (suspended sediment and particulate organic carbon) show slight clockwise hysteresis, indicating mobilization of stored sediment during rising stage. [ABSTRACT FROM AUTHOR]

Assessing and managing the spatial variability of hydropedological properties are important in environmental, agricultural, and geological sciences. The spatial variability of soil apparent electrical conductivity (ECa) measured by electromagnetic induction (EMI) techniques has been widely used to infer the spatial variability of hydrological and pedological properties. In this study, temporal stability analysis was conducted for measuring repeatedly soil ECa in an agricultural landscape in 2008. Such temporal stability was statistically compared with the soil moisture, terrain indices (slope, topographic wetness index (TWI), and profile curvature), and soil properties (particle size distribution, depth to bedrock, Mn mottle content, and soil type). Locations with great and temporally unstable soil ECa were also associated with great and unstable soil moisture, respectively. Soil ECa were greater and more unstable in the areas with great TWI (TWI > 8), gentle and concave slope (slope < 3%; profile curvature > 0.2). Soil ECa exponentially increased with depth to bedrock, and soil profile silt and Mn mottle contents (R = 0.57), quadratically (R = 0.47), and linearly (R = 0.47), respectively. Soil ECa was greater and more unstable in Gleysol and Nitosol soils, which were distributed in areas with low elevation (< 380 m), thick soil solum (> 3 m), and fluctuated water table (shallow in winter and spring but deep in summer and fall). In contrast, Acrisol, Luvisol, and Cambisol soils, which are distributed in the upper slope areas, had lower and more stable soil ECa. Through these observations, we concluded that the temporal stability of soil ECa can be used to interpret the spatial and temporal variability of these hydropedological properties. [ABSTRACT FROM AUTHOR]

Soil physical characteristics can influence terrestrial hydrology and the energy balance and may thus affect land-atmosphere exchanges. However, only few studies have investigated the importance of soil textures for climate. In this study, we examine the impact of soil texture specification in a regional climate model. We perform climate simulations over Europe using soil maps derived from two different sources: the soil map of the world from the Food and Agricultural Organization and the European Soil Database from the European Commission Joint Research Center. These simulations highlight the importance of the specified soil texture in summer, with differences of up to 2 °C in mean 2-m temperature and 20 % in precipitation resulting from changes in the partitioning of energy at the land surface into sensible and latent heat flux. Furthermore, we perform additional simulations where individual soil parameters are perturbed in order to understand their role for summer climate. These simulations highlight the importance of the vertical profile of soil moisture for evapotranspiration. Parameters affecting the latter are hydraulic diffusivity parameters, field capacity and plant wilting point. Our study highlights the importance of soil properties for climate simulations. Given the uncertainty associated with the geographical distribution of soil texture and the resulting differences between maps from different sources, efforts to improve existing databases are needed. In addition, climate models would benefit from tackling unresolved issues in land-surface modeling related to the high spatial variability in soil parameters, both horizontally and vertically, and to limitations of the concept of soil textural class. [ABSTRACT FROM AUTHOR]

Nutrient fluxes in terrestrial ecosystems are governed by complex biological and physical interactions. Ecologists’ mechanistic understanding of these interactions has focused on biological controls including plant uptake and microbial processing. However, ecologists and hydrologists have recently demonstrated that physical controls are also important. Here, we show that within-site spatial variation in soil solution N concentrations is a function of soil clay content across a globally diverse array of field sites. Clay content explained 35 and 53% of the coefficient of variation (CV) in soil solution nitrate (NO3 −) and dissolved organic nitrogen (DON), respectively. The CV of soil hydraulic conductivity is a similar function of clay content, suggesting that soil hydrology may be a significant mechanism affecting variation in soil solution N. Although vegetation physiognomy and soil C/N ratios are known to affect soil solution N concentrations, neither was significantly related to within-site spatial variation in NO3 − or DON. However, the spatial variation of NO3 − and DON was greater in younger forests than in paired older forests. Our data show that the heterogeneity of an important resource, soil solution N, is a predictable function of clay content. Resource heterogeneity, such as that described here for soil solution N, can affect population, community, and ecosystem processes. [ABSTRACT FROM AUTHOR]

Ecosystem analysis is typically done by determination of species composition, structural exploration, determination of matter and energy fluxes and/or system analyses based on deterministic or probabilistic/stochastic model approaches. However, regarding ecosystem dynamics, temporal structure, information content, complexity of signals, and their modifications when subsequently passing through different subsystems, have not intensively been studied to date. Structure in time series characterised by information and complexity measures may provide additional, powerful tools to analyse state and dynamics of ecosystems. Along their path through ecosystem compartments, e.g., hydrological signals are transformed in several ways, comprising changes in randomness, autocorrelation structures, and smoothness. Thus, time series analyses with complexity and information measures are of interest for a holistic understanding of ecosystem behaviour and early indications of natural and anthropogenic disturbances of ecosystems such as ecosystem degradation and climate change. Further, these measures provide additional criteria for the calibration of model parameters, tests of model validity, and determination of the necessary degree of complexity of process models. In this paper, we present the outcome from applications of information and complexity measures to hydrological time series in two climatically different forest ecosystems in South Germany and southern Ecuador. Information and complexity measures are different for different parameters but ecosystems of the same type such as mountain forests exhibit similar behaviour. We hypothesise that complexity of hydraulic time series increases with the number of abiotic and biotic variables involved in the generating process of the time series. Thus, complexity should reach a minimum in the precipitation signal which is controlled by abiotic, atmospheric factors only, and reach a maximum in the root zone where the interaction of abiotic and biotic variables is high. Hydrological time series under study cover the sequence of hydrological signals from open precipitation, throughfall, sapflow, water fluxes in the soil compartment and system discharge. We detected pronounced data aggregation and transformation effects of hydrological signals along their path through subsystems in terms of information propagation. We further found similar patterns in different ecosystems of the same general type. As a result of intensive abiotic and biotic interactions, a pronounced maximum of complexity was found in the moisture signal of the soil compartment. [ABSTRACT FROM AUTHOR]

Different methods exist for measuring soil water and solute fluxes in and below the root zone and have been critically reviewed. Besides indirect methods (e.g. water balance, tensiometer, time domain reflectometry – TDR, frequency domain reflectometry – FDR, environmental tracer) direct methods (e.g. drainage-type lysimeter, water fluxmeter) have a long tradition and have been successfully used in seepage research. A large weighable out door lysimeter is the best method for obtaining reliable data about seepage water quantity and quality, but it involves significant investment and additional expenses for maintenance. To tackle this problem new methods for the vertical collection of large volume soil monoliths (up to 6 m3) as well as for the horizontal collection (up to 6 m3) have been developed. For the placement of the lysimeter a container lysimeter unit was constructed, which is cheaper than a conventional steel or concrete cellar. Furthermore, the technical design of the newly developed lysimeter types as a weighable gravitation lysimeter, a weighable groundwater lysimeter and a lateral flow lysimeter are presented. [ABSTRACT FROM AUTHOR]

Soil hydrological properties like infiltration capacity and hydraulic conductivity have important consequences for hydrological properties of soils in river catchments and for flood risk prevention. They are dynamic properties due to varying land use management practices. The objective of this study was to characterize the variation of infiltration capacity, hydraulic conductivity and soil organoprofile development on forest sites with comparable geological substrate, soil type and climatic conditions, but different stand ages and tree species in terms of the effects of forest transformation upon soil hydrological properties. The Kahlenberg forest area (50 km northeast of Berlin in the German northeastern lowlands) under investigation contains stands of Scots pine ( Pinus sylvestris) and European beech ( Fagus sylvatica) of different age structures forming a transformation chronosequence from pure Scots pine stands towards pure European beech stands. The water infiltration capacity and hydraulic conductivity (K) of the investigated sandy-textured soils are low and very few macropores exist. Additionally these pores are marked by poor connectivity and therefore do not have any significant effect on water infiltration rate. Moreover, water infiltration in these soils is impeded by their hydrophobic properties. Along the experimental chronosequence of forest transformation, the thickness of the forest floor layer decreases due to enhanced decomposition and humification intensities. By contrast, the thickness of the humous topsoil increases. Presumably, changes in soil organic matter storage and quality caused by the management practice of forest transformation affect the persistence and degree of water repellency in the soil, which in turn influences the hydraulic properties of the experimental soils. The results indicate clearly that soils play a crucial role for water retention and therefore, in overland flow prevention. There is a need to have more awareness on the intimate link between the land use and soil properties and their possible effects on flooding. [ABSTRACT FROM AUTHOR]

— Shallow landslides are often linked to high magnitude rainstorms. Research has attempted to establish threshold rainfall totals that trigger shallow landslides, based mainly on field evidence. Complications arise because not all regolith has the same hydrological behaviour, and research frequently fails to take this into account. This paper uses a combination of field and modelling approaches to explore the triggering rainfall thresholds for shallow failures in deforested hill country of New Zealand. It emphasises the role of variations in regolith hydrology, focussing on unsaturated and saturated zone responses. By using a modelling approach, detailed variations in pore pressure (positive and negative) responses are investigated, developing ideas initially derived from field evidence. This paper defines and develops earlier research that establishes values for maximum and minimum probability thresholds for shallow landslides, and provides a more generalised model that can be applied more widely. Hydrological mechanisms for shallow landslides are investigated in greater detail than previously possible using a Combined Hydrology And Stability Model (CHASM™). [ABSTRACT FROM AUTHOR]

We investigated the relationships between foliar stable carbon isotope discrimination (Δ), % foliar N, and predawn water potentials (ψpd) and midday stomatal conductance (gs) of Larrea tridentata across five Mojave Desert soils with different age-specific surface and sub-surface horizon development and soil hydrologies. We wished to elucidate how this long-lived evergreen shrub optimizes leaf-level physiological performance across soils with physicochemical characteristics that affect the distribution of limiting water and nitrogen resources. We found that in young, coarse alluvial soils that permit water infiltration to deeper soil horizons, % foliar N was highest and Δ, gs and ψpd were lowest, while %N was lowest and Δ, gs and ψpd were highest in fine sandy soils; Larrea growing in older soils with well-developed surface and sub-surface horizons exhibited intermediate values for these parameters. Δ showed negative linear relationships with % N (R2=0.54) and a positive relationship with ψpd (R2=0.14). Multiple regression analyses showed a strong degree of multicolinearity of gs and Δ with ψpd and N, suggesting that soil-mediated distribution of co-limiting water and nitrogen resources was the primary determinant of stomatal behavior, which is the primary limitation to productivity in this shrub. These findings show that subtle changes in the soil medium plays a strong role in the spatial and temporal distribution and utilization of limiting water and nitrogen resources by this long-lived desert evergreen, and that this role can be detected through carbon isotope ratios. [ABSTRACT FROM AUTHOR]

A process-based model was built to describe the ecological processes of an alkalinized–salinized meadow steppe ecosystem, including the hydrological and alkalization–salinization processes in the soil, as well as the succession and growth dynamics of the grassland communities. A numerical integration model and a water and salt balance model were integrated into a physically-based model, describing the dynamics of soil moisture, salt concentration, exchangeable sodium percentage (ESP) and pH. Meteorological variables and soil characteristics were the main environmental factors used to estimate the growth dynamics of three herbaceous communities that were dominated by Aneurolepidium chinense, Chloris virgata, and Suaeda glauca, respectively. Model validation showed good agreement between the simulated results and the observed data. Simulation studies were conducted to evaluate the potential changes in hydrological and alkalization–salinization processes, succession and growth dynamics from 1991 to 1998, under five grazing intensities, namely 0%, 25%, 50%, 75% and 90% above-ground biomass removal (AGBR). The simulations show that soil moisture decreased markedly under the 50%, 75% and 90% AGBR, but increased slightly under the 25% AGBR. The de-alkalization and de-salinization processes would be predominant under the 0% AGBR, and the processes became a little slower under the 25% AGBR. In contrast, the 50%, 75% and 90% AGBR accelerated the degradation of soil properties. The grassland was dominated by A. chinense under the 0% AGBR, and by A. chinense and C. virgata under the 25% AGBR. C. virgata could grow on slightly alkalinized–salinized soil and became a dominant species after three years of 50% AGBR. The soil degraded quickly and only S. glauca could grow on the severe alkalinized–salinized soil if the grassland received 75% or 90% AGBR. The grassland grew well under the 0% AGBR, and the biomass stayed at moderate level under 25% AGBR. The 50%, 75% and 90% AGBR decreased the grassland growth greatly. After accumulating the grazed biomass for each year, the 25% AGBR would provide the highest production, and the grassland production would decrease sharply with the increasing of grazing intensities. The simulation results indicate that 25% AGBR is significant for preserving the soil from degradation, and maintaining high grassland production. [ABSTRACT FROM AUTHOR]