Vertical Movement Of Moisture Research Articles

Effect of cavity structure on the saving up and dissipation of moisture in loess soil

Technique of loess cavity structure is a kind of technology which can increase the seepage volume of rainfall water and prolong the storage time of water in the soil, but popularization and application of the technology needs theoretical support. This paper uses the method of combining indoor experiment to study the laws of water storage and evaporation dissipation in the loess soil with cavity structure under heavy rain. Results show that, vertical movement of moisture in the soil profile shows as hierarchy, and the cavity layer is the high water-holding-capacity zone; presence of the cavity structure retains more water in the soil body, reduces or prevents the water leakage to the deeper soil, and increases the water storage capacity of the loess soil by 4.7%; cavity structure can reduce the soil evaporation of 12.6%, and significantly inhibits soil evaporation. The study confirms the remarkable function of seepage improved and anti-evaporation of loess cavity structure technology, thus build a solid theoretical basis for the popularization and utilization of it.

Strong seasonal connectivity between shallow groundwater and soil frost in a humid alpine meadow, northeastern Qinghai-Tibetan Plateau

The freeze-thaw cycle in the active soil layer plays a crucial role in cold-region hydrological processes, yet the effect of vertical water migration caused by the soil frost on shallow groundwater remains poorly quantified. The shallow groundwater level (GWL), soil frost depth and main environmental controls were monitored in a humid alpine meadow on the northeastern Qinghai-Tibetan Plateau from 2012 to 2017. GWL fluctuated with two seasonal maxima and minima during soil frost-centric year from November to October. GWL declined remarkably from the strong peak (3.9 ± 0.2 m, Mean ± S.D.) in mid-January to the strong minimum (4.8 ± 0.1 m) in mid-May, and then increased to the second peak (4.2 ± 0.2 m) in late August. This seasonal variability in GWL was mainly attributed to the freeze-thaw processes of the lower layer soil frost from November to late June both at a ∼45-day delay, respectively. The clear increasing GWL from mid-November to mid-January was probably related to the melted upper layer soil frost, which was detained in subsoil layers because of the high thermal isolating effect in topsoil Mattic Epipedon (dense organic-rich turf) and the associated negative subsoil profile temperature gradient from mid-May to late August. The seasonal N-type in GWL was thus hysteretically determined by the soil freeze-thaw processes and the related subsoil profile temperature gradient. Annually, GWL was significantly correlated with air temperature (R2 = 0.88, P = 0.003, N = 6), suggesting the shallow groundwater recharges would be weakened under the warming scenario. Annual GWL was not directly connected with annual precipitation (P = 0.81), likely owing to the high water holding capacity of the topsoil Mattic Epipedon and the similarity between precipitation input and evapotranspiration loss. This critical buffering function of the topsoil Mattic Epipedon in vertical moisture movement should be taken into consideration when modeling regional water dynamics in humid alpine meadows.

Seasonal dynamics and controls of deep soil water infiltration in the seasonally-frozen region of the Qinghai-Tibet plateau

Deep soil water infiltration is a key hydrological process in seasonally frozen regions, and displays a distinct behavior from that in other unfrozen regions; however, the seasonal dynamics and key controls of deep soil water infiltration in the seasonally frozen region of the Qinghai-Tibet plateau (QTP) are still poorly understood. In this study, we examine the seasonal dynamics of deep soil water infiltration, and attempt to quantitatively assess the relative influences of several driving factors by applying a random forests statistical analysis. The following key results were obtained. Deep soil water infiltration shows marked seasonal variation. Rainfall intensity exerts little effect on the seasonal dynamics of deep soil water infiltration as almost all rainfall returns to the atmosphere via evapotranspiration. No infiltration occurred when the depth of lower layer frozen soil reached 29 cm, whereas deep infiltration increased during the thawing of soil frost, suggesting that deep infiltration is impeded by soil freezing. Overall, the observed seasonal dynamics of deep soil water infiltration and volumetric soil moisture content were similar during the freeze-thaw process. Furthermore, deep soil water infiltration was more strongly influenced by deep volumetric soil moisture than by shallower volumetric soil moisture. Our results suggest that the topsoil Mattic Epipedon, soil organic matter content, and root systems’ role in vertical moisture movement should be taken into consideration when modeling hydrological processes in alpine meadows.

Energy balance in the semiarid area of the Loess Plateau, China

AbstractTo understand the energy balance over the complex terrain of the Loess Plateau, we analyzed data from the Semi‐Arid Climate and Environment Observatory of Lanzhou University (SACOL). From 1 June to 15 August 2008, the energy balance closure ratio ranged from 0.52 to 0.90 during the daytime when the available energy was greater than 150 W m−2; during nocturnal hours, it was about 0.25. We proposed a method based on water mass conservation to estimate the energy transmitted by the vertical movement of moisture in the soil and set out to explain the imbalance. During the daytime, the heat stored in the soil above the heat flux plate placed at 5 cm below the surface, the energy transmitted by the vertical movement of moisture in the soil, and the energy assimilated by plant photosynthesis contributed to 29.6%, 2.0%, and 1.8% of the energy residual, respectively. During stable conditions, the soil heat storage contributed to 46.4% of the energy residual, whereas the other energy terms contributed little. The instantaneous energy closure ratio was about 0.80 during unstable conditions; it was about 0.40 when the wind speed U was greater than 3.0 m s−1, while depends systematically on U under condition of U < 3.0 m s−1 during stable conditions. Under the weak wind stable condition, affected by topography‐induced nonstationary motions, the turbulence is anisotropic with a strong horizontal fluctuation and a weak vertical fluctuation, resulting in weakened heat mixing in the vertical direction and stronger unclosure of energy.

The problems of water resources in North China and the strategy

North China, whose total area is 420,000 km2, covers 2 provinces and 2 cities (Shanxi and Hebei provinces, Beijing and Tianjin) and the territories of Henan and Shandong provinces to the north of the Huanghe (Yellow) River, and part of the Inner Mongolia Autonomous Region and Liaoning Province. Most of this region, which is situated in the semi-humid, semi-arid continental climate temperate zone, gets an annual precipitation of 500–600 mm, whereas, the perennial average amount of total water resource is 50.99 billion m3, including 33.82 billion m3 of surface water, 32.94 billion m3 of ground water and 15.77 billion m3 of their duplication. Due to the intensive exploitation of water resource caused by the deficiency of water resource in North China, key elements of water balance was changed, runoff volume reduced, evaporation increased, vertical movement of moisture strengthened, water circulation pattern transformed from open system into regionally closed system; meanwhile, due to the incompetent water purification system in comparison with the wastewater discharge, the pollution of water bodies goes bad to worse. Furthermore, some water bodies becomes unusable. The reduction in runoff amount, both surface and under ground, and the pollution of water body cause a series of environmental problems. The essential contributing factors of the water resources problems in North China are the deficiency of water resource and water pollution. The deficiency was mainly caused by fast increase in water consumption and water pollution, besides the fragility of local natural conditions. The deficiency is consequently brought about by population growth and economic development incoordinate with local circumstance. The strategies to deal with the water resources problems should include the following aspects: 1) the establishment of water-saving economy and society, 2) proper management and rational utilization of water resources, 3) the exploitation of new water resources, and 4) the improvement of wastewater treatment ability.

Stochastic modeling of large‐scale flow in heterogeneous unsaturated soils

A simulation experiment is used to test the stochastic theory of unsaturated flow proposed by Mantoglou and Gelhar (1987a, b, c). Tension means and variances derived from this theory are compared to tension distributions obtained from a detailed three‐dimensional model developed by Ababou (1988). The synthetically generated unsaturated hydraulic conductivity functions used in the detailed model vary significantly over relatively small distances. Results from a simulated infiltration event indicate that the stochastic theory's predictions reproduce the overall trend of the heterogeneous tension distribution. Deviations from the predicted mean generally lie within confidence intervals derived from the predicted variance. The stochastic theory predicts less vertical moisture movement and somewhat more horizontal spreading than a comparable deterministic analysis. This reflects the fact that the effective hydraulic conductivity function used in the stochastic approach is anisotropic. The magnitude of this anisotropy increases with increasing tension.

FUNDAMENTAL STUDY ON MIGRATION AND ACCUMULATION OF SOLUTE IN UNSATURATED ZONE OF SOIL COLUMN BY EVAPORATION

The evaporation from soil surface and solute migration in an unsaturated zone above the groundwater are studied experimentally and theoretically. The experimental apparatus used in this study consists of a wind tube, soil column, groundwater feeding tank and a set of measurement equipments. The vertical profiles of solute concentration, temperature and water content along soil column, and the evaporation rate from soil surface are measured for different wind velocities.The analytical solutions of governing equations at the steady state are developed for solute migration in coupling with heat transport and moisture movement. The comparison between analytical solutions and experimental results shows an excellent agreement. The results describe that the solute migration depends upon not only vertical movement of moisture but also a depth of capillary fringe.

Fundamental study on migration of nuclides in underground disposal of low-level radioactive waste

In order to clarify the mechanism of solute migration in an unsaturated zone of soil stratum, the basic experiments on the upward and downward movements of water and solutes (NaCl, Sr, Co, Cs) under the artificial environment (rainfall-evaporation cycles) were carried out. The experimental apparatus used in this study consists of a large soil box, nozzles of rain-fall, infrared lamps, thermometer sensors, recorders and sampling tubes. The vertical profiles of solute concentration, temparature and water content in the unsaturated zone above the groundwater are measured for different groundwater depth. The analytical solutions of governing equations at the steady-state are derived. The comparison between solutions and experimental results shows a good agreement. The results describe that the solute migration depends upon not only vertical movement of moisture but also a depth of capillary fringe.