Deep Soil Water Content Research Articles

Spatial and temporal variability of 0‐ to 5‐m soil–water storage at the watershed scale

AbstractDynamic 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.

Sustainability of Abandoned Slopes in the Hill and Gully Loess Plateau Region Considering Deep Soil Water

Soil desiccation of the deep soil layer is considered one of the main limiting factors to achieving sustainable development of ecosystems in the hill and gully Loess Plateau region. In this study, slope croplands were selected as the control, and deep soil water was studied on abandoned slopes, including natural abandoned slopes, Robinia pseudoacacia plantations, and Caragana korshinskii plantations. Then, we explored deep soil water characteristics of different vegetation types and slope aspects and the variation tendencies of deep soil water at different recovery stages. The results showed that there were no significant differences in deep soil water content between sunny and shady slopes, and thus, slope aspect was not the key impact factor affecting deep soil water. Deep soil water content on R. pseudoacacia plantations and C. korshinskii plantations was lower than that on natural abandoned slopes; there were no significant differences in soil water content between the natural abandoned slopes and slope croplands. Soil desiccation did not exist on natural abandoned slopes; thus, natural vegetation restoration is an appropriate way to achieve a sustainable ecosystem with respect to deep soil water. In contrast, soil desiccation intensified until it was difficult for vegetation to obtain available water in the deep soil layer on the plantations; soil desiccation began to appear at the 11–20-year stage, and it became increasingly severe until the deep soil water was close to the wilting coefficient at the ≥30-year stage on R. pseudoacacia plantations. Deep soil water was rapidly consumed, and soil desiccation began to appear at the 1–10-year stage and then was close to the wilting coefficient in the later stages on C. korshinskii plantations. According to the results, the plantations needed to be managed in a timely manner to prevent or reduce soil desiccation.

Evaluating the Timing and Interdependence of Hydrologic Processes at the Watershed Scale Based on Continuously Monitored Data

A quantitative understanding of the interplay between the different components of the hydrologic cycle at the watershed scale can be gained from analyzing high-frequency hydrologic time series. High-frequency measurements of precipitation, soil water content, shallow groundwater, and streamflow were collected and analyzed in Otter Creek, a 122 km2 watershed located in Northeast Iowa, USA. For selected rainfall events occurring in 2014, it was found that there is at least 4 h of delay between soil water content and water table time series response and streamflow peak. This is true even when the water table was approximately 6.5 m below the ground surface before rainfall started. Data reveal a strong linear dependence between the soil water content and the water table, which suggests the existence of a capillary fringe that extends approximately 2.5 m above the water table. The highest streamflow values in Otter Creek occurred when both the water table was close to the ground surface and the near surface soil (top 65 cm) was close to full saturation. Analyses show that, in the study area, data on depth to water table or deep soil water content have the potential to play a key role in the development of a flood warning system. The transformation of rainfall into streamflow is a complex process that we simplified in this study. Additional analyses using physically based coupled surface-subsurface models or non-linear or stochastic models are recommended for more rigorous analysis.

Rainfall Intensification Enhances Deep Percolation and Soil Water Content in Tilled and No‐Till Cropping Systems of the US Midwest

Core Ideas Rainfall intensification increased deep percolation in tilled and no‐till systems. Rainfall intensification increased deep soil water content in both cropping systems. A bromide tracer was detected at 1.2‐m depth sooner in no‐till than tilled systems. The effect of rainfall intensification on surface soil moisture varied seasonally. Globally, the proportion of total rainfall occurring as extreme events is increasing, which may have consequences for agriculture. In the US Midwest, we conducted a 234‐d manipulative experiment in 16 paired plots where we increased the proportion of rain falling in extreme events on tilled and no‐till cropping systems. We compared the effects of larger, less frequent rain events (“intensified” rainfall) vs. smaller, more frequent rain events (“normal” rainfall) on soil water content and deep percolation. The effect of intensified rainfall on the volumetric water content (VWC) of soil at the 10‐cm depth during the experiment varied seasonally: in spring, intensified rainfall decreased the average VWC at the 10‐cm depth by 0.05 ± 0.01 cm3 cm−3 compared with normal rainfall, but in summer and fall, it had no effect. In soil at the 100‐cm depth, VWC declined during the summer in normal but not intensified plots. A surface‐added Br− tracer was detected and peaked earlier in soil water at 120 cm under intensified rainfall vs. normal rainfall (by 6 ± 3 and 74 ± 33 d, respectively) regardless of tillage, although it was detected sooner in no‐till than tilled systems (by 9 ± 3 d). Also, less Br− was recovered in soil under intensified (8 ± 8% of total Br− added) vs. normal rainfall (21 ± 3%). Our results suggest that rainfall intensification will increase deep percolation and deep soil water content in cropping systems regardless of tillage. Such changes to soil water dynamics may alter plant water and nutrient availability.

Effects of land use types on deep soil water content in the loess hilly area of the north Shaanxi Province, China

This study explored the differences of soil water content at 0-20 m soil depth at three locations, including economical plantation in Mizhi, reforestation area in Shenmu, and wind break and sand fixation forest district of Yuyang, and for clarifying the impacts of different land use types on deep soil water distribution and storage characterization, as well as its eco-environmental effect on the loess hilly area. The results showed that in the soil profile of 0-20 m, land use patterns had a significant impact on soil moisture distribution. There were significant differences of soil water sto-rage for the economical plantation, pruning Ziziphus jujuba plantation ＞ Z. jujuba plantation with 587.9 mm difference. There was no significant difference in soil water storage between Caragana korshinskii plantation and degraded artificial vegetation or between pine forests and natural grass field, degraded artificial grassland ＞ C. korshinskii plantation with 98.8 mm difference at Shenmu, and natural grassland ＞ Pinus sylvestris var. mongolica plantation with 7.5 mm difference at Yuyang. The pruning Z. jujuba tree reduced soil water consumption and was beneficial to sustainable use of soil water due to the decreased crown width and thus reduced transpiration. There were no obvious differences of soil water content between C. korshinskii plantation and degraded artificial grassland due to the historical alfalfa planting which was characterized by high water consumption due to its deep root distribution and large biomass. In contrast, P. sylvestris var. mongolica plantation and na-tural grassland had similar and low averaged soil water contents with 3.4% and 3.6%, respectively, mainly due to the sandy soil texture and weak soil water holding capacity. In addition, with increa-sing soil depth, soil water content increased in this area, indicating the effect of plants on water moisture of deep soil was very limited. Except for the underlying control of soil texture on soil water content in the soil profile, different vegetation played a key role in the dynamics of soil water content due to the difference of root zones. It was very important to choose the suitable type of vegetation regarding the protection and sustainable use of deep soil water.

Vertical distribution and temporal stability of soil water in 21-m profiles under different land uses on the Loess Plateau in China

Deep soil-water content (SWC) plays a crucial role in water-limited terrestrial ecosystems, because plant roots can extract soil water from depths of 20 m or more. The distribution of soil water and its temporal variation in deep (>5 m) soil profiles are not completely understood, partly due to the time and labor needed for their determination. We examined the vertical distribution patterns and temporal stabilities of soil water in 21-m soil profiles for two years under four typical land use types in the Liudaogou watershed of the Chinese Loess Plateau (CLP). The SWCs exhibited considerable variability over both depth and time under farmland, natural grassland, planted grassland, and shrubland. The soil profile could be partitioned into an active layer (0-2 m) and a relatively stable layer (2-21 m) based on the amount of temporal change in SWC. The mean available soil water contents (AWCs) among the land use types in the depth-time domain differed significantly (P natural grassland (6.5%) > planted grassland (5.7%) > shrubland (4.9%). The mean available soil water storage for each 1-m-depth (AWS(1m)) in the 0-21 m profile, in the time domain, ranged from 50.3 to 71.4 mm among the four land use types. Within the 21-m profile, as the depths of sub-profiles increased from 3 m to 21 m, the most temporally stable depths (MTSDs) of AWS(1m) tended to become deeper in a step-like manner, producing ranges of MTSDs of 3-18 m, 2-15 m, 2-9 m, and 3-20 m under farmland, natural grassland, planted grassland, and shrubland, respectively. The ability of the MTSDs to estimate the mean AWS(1m) in a soil profile was generally acceptable for each sub-profile, as indicated by the RMSD and RBIAS values obtained from a validation dataset, which ranged from 3.6 to 7.7 mm and from 0.07 to 0.13, respectively, among the four land use types. The mean AWS(1m) within the 21-m profile could, in general, be accurately estimated by measuring AWC to a depth of only 18 m based on the temporal stability analysis. Land use greatly affected the vertical distributions and temporal stabilities of the AWC in the deep soils. The knowledge obtained from this information is vital for the sustainable use of water resources, rational management of various land uses, and scientific determinations of soil water in deep soils on the CLP and possibly in other fragile ecosystems covered by deep soils around the world. (C) 2015 Elsevier B.V. All rights reserved.

The limiting effect of deep soilwater on evapotranspiration of a subtropical coniferous plantation subjected to seasonal drought

Seasonal drought is a common occurrence in humid climates. The year 2003 was the driest year during the period 1985–2011 in southeastern China. The objective of this study was to elucidate the impact of the exceptional drought in 2003, compared with eddy flux measurements during 2004–11, on the dynamics of evapotranspiration (ET) and related factors, as well as their underlying mechanisms, in a subtropical coniferous plantation in southeastern China. It was found that daily ET decreased from 5.34 to 1.84 mm during the intensive drought period and recovered to 4.80 mm during the subsquent recovering drought period. Path analysis indicated that ET was mainly determined by canopy conductance and deep soil water content (50 cm) during the intensive drought and recovering drought periods, respectively. The canopy conductance offset the positive effect of air vapor pressure deficit on ET when suffering drought stress, while the canopy conductance enhanced the positive effect of air temperature on ET during the late growing season. Because the fine roots of this plantation are mainly distributed in shallow soil, and the soil water in the upper 40 cm did not satisfy the demand for ET, stomatal closure and defoliation were evident as physiological responses to drought stress.

Efecto de la transpiración sobre la escorrentía en dos tipos de bosque de la cordillera de la costa, sur de Chile

(Recibido: 2013/09/03 - Aceptado: 2013/11/20)En esta investigación se comparó la tasa de transpiración y su efecto en la escorrentía en dos microcuencas con bosque nativo siempreverde (Bonifacio) y deciduo (Las Palmas) durante el cambio estacional primavera-verano. Las variables utilizadas fueron precipitación, escorrentía, índice de área foliar, transpiración de especies, y distribución del agua en el suelo. Los resultados mostraron un mayor consumo de agua en el bosque deciduo traduciéndose en una mayor evapotranspiración con 2273,6 mm en comparación al bosque siempreverde con 1740 mm, generando una mayor escorrentía en este último. La comparación entre los índices de área foliar de los dos bosques mostraron diferencia, sobretodo en la primavera para el bosque deciduo, ya que al aumentar su tasa transpiratoria por incremento de biomasa, generó una menor escorrentía a pesar que existieron mayores precipitaciones. Además las especies del bosque siempreverde consumieron el agua de los primeros centímetros (10-20) del perfil del suelo a diferencia del bosque deciduo, donde se observó una disminución en la humedad del suelo a una profundidad un poco mayor (40 cm). En cuanto al rendimiento hídrico, se pudo mostrar con este trabajo que el bosque siempreverde es más eficiente que el bosque deciduo durante el período de activo crecimiento primavera-verano.

Impacts of extreme precipitation on tree plantation carbon cycle

Extreme precipitation events are expected to increase in frequency and magnitude in future due to global warming, but relevant impacts on tree plantation ecosystem carbon cycle are unknown. In this study, we use an atmosphere–vegetation interaction model (AVIM2) to estimate the likely impacts of extreme precipitation events on carbon fluxes and carbon stocks of a tree plantation in south China. Our results indicate that shifting from moderate precipitation events to extreme precipitation events whilst keeping monthly precipitation unchanged could decrease the tree plantation carbon accumulation. Tree plantation net primary productivity, net ecosystem productivity, soil carbon stock and vegetation carbon stock could decrease by 4.2, 28, 4.3 and 1.4 % during the studying period of 1962–2004, respectively. Though reductions in net primary productivity and net ecosystem productivity are relatively smaller than their annual variations, our sensitivity test shows that the tree plantation carbon stock could decrease by 3.3 % if the assumed extreme precipitation regime lasts for 500 years. Observed and simulated gross primary productivity, ecosystem respiration and net ecosystem productivity have significant positive correlation with soil water content (SWC), especially the deep SWC. The mechanism for the extreme precipitation effect is that the increase in extreme precipitation events will cause SWC to decrease, consequently, reducing carbon fluxes and stocks.

Effect of sand-stabilizing shrubs on soil respiration in a temperate desert

Explore how soil CO2 efflux and its components change after moving sand dunes are stabilized with shrubs, and how abiotic factors affect those components at different scales. Soil CO2 efflux from a sand-stabilized area was compared to that from moving sand dunes in the Tengger Desert. To partition rhizosphere respiration (RR) from soil basal respiration (RB), a root-isolation plot was established. Compared to moving sand dunes, total soil respiration (RT) in the sand-stabilized area increased 3.2 fold to 0.28 ± 0.08 μmol CO2 m-2 s-1, two thirds of which was from RB. Shrub patchiness produced spatial variation in soil respiration, whereas temporal dynamics of soil respiration were affected mainly by soil water content. Shallow soil water content (0–20 cm) influenced RT and RB, whereas deep soil water content (30–210 cm) influenced RR and the ratio RR/RT. During most of the year when soil water content was below field capacity, diurnal changes in soil respiration were partially decoupled from soil temperature but could be modeled using soil temperature and photosynthetic active radiation. Sand-dune stabilization increased soil respiration, and increased RB from biological soil crust and altered soil properties such as increased soil organic matter contributed more than increased RR from increased shrubs.

Regional spatial pattern of deep soil water content and its influencing factors

Plant root systems can utilize soil water to depths of 10 m or more. Spatial pattern data of deep soil water content (SWC) at the regional scale are scarce due to the labour and time constraints of field measurements. We measured gravimetric deep SWC (DSWC) at depths of 200, 300, 400, 500, 600, 800 and 1000 cm at 382 sites across the Loess Plateau, China. The coefficient of variation was high for soil water content (SWC) in the horizontal direction (48%), but was relatively small for SWC in the vertical direction (9%). Semivariogram ranges for DSWC at different depths were between 198 and 609 km. Kriged distribution maps indicated that deep soil layers became moister along northwest to southeast transects. Multiple statistical analyses related DSWC to plant characteristics (e.g. plant age explained >21% of the variability), geographical location and altitude (8–13%), soil texture and infiltrability, evaporation zone and eco-hydrological processes (P < 0.05). Regional land management decisions can be based on our DSWC distribution data to determine land uses and plant species appropriate for the soil type and location that would maintain a stable soil water balance. Maintaining infiltrability is of great importance in this and other water-scarce regions of the world. Editor D. Koutsoyiannis; Associate editor J. Simunek Citation Wang, Y.Q., Shao, M.A., Liu, Z.P. and Warrington, D.N., 2012. Regional spatial pattern of deep soil water content and its influencing factors. Hydrological Sciences Journal, 57 (2), 265–281.

Soil particle size distribution and its relationship with soil water and salt under mulched drip irrigation in Xinjiang of China

Soil particle size distribution (PSD), one of the most important soil physical attributes, is of great importance to soil water movement, soil erosion and soil solute migration. In this study, the soil PSD of 563 soil samples from the mulched drip irrigated cotton fields in Xinjiang of China were measured by laser diffraction particle size analyzer. The soil PSD characteristics and its relations with soil water and salt were studied by using the combined methods of textural triangle, fractal and multifractal analysis. The results showed very low clay content (about 1.52%) while really high sand content of the studied soil, and a complex shape of bimodal or unimodal of soil PSD. The results also showed that the two indices, i.e., standard deviation and the peak value of soil particle relative volumes, were good indicators of soil PSD and thus had good relations with fractal and multifractal characteristics. The correlative analysis further indicated that the mulched drip irrigation had a significant impact on the distribution of the soil salt, while this impact withered for the deeper soil layer. The soil texture feature was found to dominate soil water and salt distribution, especially the surface soil salt content and the deep soil water content.

A disaggregation scheme for soil moisture based on topography and soil depth

This paper reports on a new soil moisture disaggregation scheme based on topography and soil depth information. It is designed for low resolution remote sensing data assimilation into hydrological modelling. The scheme makes use of a simple Soil Vegetation Atmosphere Transfer model coupled to the TOPMODEL formalism. Water and energy balance are computed at the catchment scale, taking lateral flows due to topography into account. Lumped values of near-surface and deep soil water content are then disaggregated at local scale using simple relationship between mean quantities, local topography and soil depth information. Results for a small water catchment in South-eastern Australia show satisfactory reproduction of the local soil moisture patterns using a combination of topography and soil depth information. Due to subgrid variability and differences between the simulation and observation scale (the Digital Elevation Model pixel versus the point measurement), the point-to-point comparison between observations and simulations shows a poor correlation. Rescaling shows that a good correlation is obtained when averaging the simulated and observed soil moisture over a length of 100 m.

The effects of partial throughfall exclusion on canopy processes, aboveground production, and biogeochemistry of an Amazon forest

Moist tropical forests in Amazonia and elsewhere are subjected to increasingly severe drought episodes through the El Niño–Southern Oscillation (ENSO) and possibly through deforestation‐driven reductions in rainfall. The effects of this trend on tropical forest canopy dynamics, emissions of greenhouse gases, and other ecological functions are potentially large but poorly understood. We established a throughfall exclusion experiment in an east‐central Amazon forest (Tapajós National Forest, Brazil) to help understand these effects. After 1‐year intercalibration period of two 1‐ha forest plots, we installed plastic panels and wooden gutters in the understory of one of the plots, thereby excluding ∼890 mm of throughfall during the exclusion period of 2000 (late January to early August) and ∼680 mm thus far in the exclusion period of 2001 (early January to late May). Average daily throughfall reaching the soil during the exclusion period in 2000 was 4.9 and 8.3 mm in the treatment and control plots and was 4.8 and 8.1 mm in 2001, respectively. During the first exclusion period, surface soil water content (0–2 m) declined by ∼100 mm, while deep soil water (2–11 m) was unaffected. During the second exclusion period, which began shortly after the dry season when soil water content was low, surface and deep soil water content declined by ∼140 and 160 mm, respectively. Although this depletion of soil water provoked no detectable increase in leaf drought stress (i.e., no reduction in predawn leaf water potential), photosynthetic capacity declined for some species, the canopy thinned (greater canopy openness and lower leaf area index) during the second exclusion period, stem radial growth of trees &lt;15 m tall declined, and fine litterfall declined in the treatment plot, as did tree fruiting. Aboveground net primary productivity (NPP) (stemwood increment and fine litter production) declined by one fourth, from 15.1 to 11.4 Mg ha−1 yr−1, in the treatment plot and decreased slightly, from 11.9 to 11.5 Mg ha−1 yr−1, in the control plot. Stem respiration varied seasonally and was correlated with stem radial growth but showed no treatment response. The fastest response to the throughfall exclusion, and the surface soil moisture deficits that it provoked, was found in the soil itself. The treatment reduced N2O emissions and increased CH4 consumption relative to the control plot, presumably in response to the improved soil aeration that is associated with soil drying. Our hypothesis that NO emissions would increase following exclusion was not supported. The conductivity and alkalinity of water percolating through the litter layer and through the mineral soil to a depth of 200 cm was higher in the treatment plot, perhaps because of the lower volume of water that was moving through these soil layers in this plot. Decomposition of the litter showed no difference between plots. In sum, the small soil water reductions provoked during the first 2 years of partial throughfall exclusion were sufficient to lower aboveground NPP, including the stemwood increment that determines the amount of carbon stored in the forest. These results suggest that the net accumulation of carbon in mature Amazon forests indicated by recent permanent plot and eddy covariance studies may be very sensitive to small reductions in rainfall. The soil water reductions were also sufficient to increase soil emissions of N2O and to increase soil consumption of CH4—both radiatively important gases in the atmosphere. The possible reduction of tree reproductive activity points to potentially important effects of drought on the long‐term species composition of Amazon forests.

A simulation of the surface energy budget and soil water content over the Hydrologic Atmospheric Pilot Experiments‐Modélisation du Bilan Hydrique forest site

The surface energy budget and soil water content variation are simulated for a two month period during the 1986 Hydrologic Atmospheric Pilot Experiment‐Modélisation du Bilan Hydrique (HAPEX‐MOBILHY) (J.C. André et al., 1988) using the Oregon State University Coupled Atmosphere Plant Snow (CAPS) model. When initialized and driven by the observed soil water content and atmospheric forcing, the CAPS model closely simulated the observed surface energy budget and the variation of soil water content. Lateral transports of soil water may cause significant impacts on the simulated soil water content during the later part of the simulation. Vegetation appears to significantly affect the surface energy budget and temporal variation of soil water content. We found two major mechanisms by which vegetation controls the surface energy budget and soil water content: (1) dependencies of transpiration on ambient conditions, and (2) direct hydrological coupling between the atmosphere and deep soil water through the root structure. Compared to the simulation without vegetation, net effects of vegetation are (1) sustained evaporation over the entire simulation period, (2) more gradual variation of near surface soil water content, and (3) continued reduction of deep soil water content through transpiration. Soil heat flux becomes an important component of the surface energy budget over a bare soil surface. The simulated surface energy budget is strongly dependent on the initial soil water content, however, dependence of the simulated surface energy budget on the initial soil temperature was relatively minor.