Effect Of Initial Soil Moisture Research Articles

Initial soil moisture conditions affect the responses of colloid mobilisation and associated cadmium transport in opposite directions

The effects of initial soil moisture on colloid-associated transport are still poorly understood given the well-recognized significance of colloid-facilitated transport of strongly-sorbing contaminants. In this study, Cd leaching was sequentially conducted in an intact soil column under three initial moisture conditions (near saturation, field capacity and dryness). Soil colloids were always the dominant carriers for Cd. However, upon the lowering of initial soil moisture, increased transport of colloids (96.2→101.0→168.2 mg) was observed, surprisingly, along with decreased transport of colloid-associated Cd (C-Cd) (23.9→10.7→8.2 µg) and enrichment factor (248.4→105.9→48.8 mg/kg) of Cd on colloids, resulting from pH reduction which increased Cd desorption and colloid size increase and/or ζ-potential decrease that showed lower affinity for Cd. Correlation, redundancy analysis and structural equation modelling revealed the dominantly positive role of colloids, EC plus cations (Ca2+ and Mg2+) in the release of C-Cd and dissolved Cd (D-Cd), respectively, under initial moistures of near saturation and field capacity. Under initially dry conditions, soil water potential showed dominantly negative effects on the transport of both C-Cd and D-Cd. These findings highlighted the critical role of initial moisture conditions in modulating colloid-facilitated Cd mobilisation, providing insights into the environmental risk assessment of heavy metals in other leaching scenarios.

Understanding the role of initial soil moisture and precipitation magnitude in flood forecast using a hydrometeorological modelling system

AbstractWe adapted the WRF‐Hydro modelling system to Hurricane Florence (2018) and performed a series of diagnostic experiments to assess the influence of initial soil moisture and precipitation magnitude on flood simulation over the Cape Fear River basin in the United States. Model results suggest that: (1) The modulation effect of initial soil moisture on the flood peak is non‐linear and weakens as precipitation magnitude increases. There is a threshold value of the soil saturation, below and above which the sensitivity of flood peak to the soil moisture differentiates substantially; (2) For model spin‐up, streamflow needs longer time to reach the ‘practical’ equilibrium (10%) than the soil moisture and latent heat flux. The model uncertainty from spin‐up can propagate through the hydrometeorological modelling chain and get amplified into the flood peak; (3) For ensemble flood modelling with a hydrometeorological system, modelling uncertainty is dominated by the precipitation forecast. Spin‐up induced uncertainty can be minimized once the model reaches the ‘practical’ equilibrium.

A simple method for correcting the effects of initial soil moisture on Modified Philip-Dunne Infiltrometer drawdown curves

The effect of varying initial soil moisture (θin) of a given soil on the drawdown curve measured using the Modified Philip-Dunne Infiltrometer (MPDI) and consequently on the estimated saturated hydraulic conductivity (Κs) value, was investigated. The laboratory tests completed using three different types of soil show that the drawdown curve was sensitive to θin for all three soils. This resulted in yielding Κs values that are sensitive to the values of θin. The lowest value of Κs was observed when the MPDI was used under wet conditions. To obtain a consistent estimate of Κs, a new correction factor was developed. This factor can be multiplied with the geometrical coefficient used in the governing equations of the MPDI to make appropriate corrections. After employing the correction factor, the variations in Κs values for all three tested soils decreased from 66%, 61% and 59%, to 26%, 16% and 26%, respectively. In situ experimental tests also show similar results and the coefficient of variation decreased from 81% to 61% after applying the correction factor. The performance was further validated by testing the relative performance of the MPDI against the results obtained using Minidisk Infiltrometer (MDI) under varying θin values. Results from the MDI show that the coefficient of variation for the Κs values of the three soils were 20%, 28%, and 32%, which are similar to the variations obtained after applying the correction factor in the MPDI model calculations. The aforementioned results indicate that the correction method proposed in this study is a useful method for improving the overall performance of MPDI.

Hydrologic Performance of an Extensive Green Roof in Syracuse, NY

Green roof performance reported in literature varies widely—the result of differences in green roof design and climate, as well as limitations in study design and duration. The need exists for full-scale studies under real climate conditions to inform the design, modeling, and planning of new green roof installations. The purpose of this study is to quantify hydrologic performance of a large green roof and characterize its dominant physical processes. To achieve this, a 5550 m2 extensive green roof in Syracuse, New York, designed to hold a 25.4 mm rain event, is monitored for 21 months. Over the monitoring period, the roof retains 56% of the 1062 mm of rainfall recorded. Peak runoff is reduced by an average of 65%. Eleven events exceed 20 mm and are responsible for 38% of the rainfall and 24% of the annual retention. Retention in the summer is lower than that in the fall or spring, as a result of greater rainfall intensity during the period sampled. Soil moisture during winter months remains high, reducing the ability of the roof to retain rainfall volume from new events. Comparison of seasonal data demonstrates the strong influence of rainfall intensity on runoff and the effect of initial soil moisture on event retention.

Effects of Initial Soil Moisture, Clod Size, and Clay Content on Ammonia Volatilization after Subsurface Band Application of Urea.

Ammonia losses from broadcast urea vary based on soil physical and chemical properties; however, less is known about how soil properties affect NH losses after subsurface banding of urea. Therefore, three field trials were established to determine how initial soil moisture, clod size, and clay content affect NH volatilization from subsurface-banded (0.025-m depth) urea using wind tunnels. The first study measured volatilization after banding in a loamy mixed frigid Typic Humaquept at 50, 100, 150, 200, or 250 g kg gravimetric water content (WC). Study 2 measured volatilization from the same soil after covering the bands with soil clods that ranged from <2 to >24 mm in diameter, whereas Study 3 measured volatilization from transplanted, acidic soils with clay contents ranging from 5 to 57%. Cumulative 17-d NH losses for study one ranged from 8.3 to 20.8% of applied N, with the soil wetted to 200 g kg WC experiencing the greatest losses. For Study 2, cumulative NH volatilization losses ranged from 10.8 to 20.8% of applied N, with the greatest losses from the largest clod sizes. For Study 3, NH losses ranged from 2.5 to 51.7% of applied N, with the NH losses correlated to the maximum pH measured in the band ( < 0.001), and to the soil cation exchange capacity ( = 0.054), titratable acidity ( = 0.072), and clay content ( = 0.100). However, the soil with high silt, not sand, content had the highest volatilization losses, suggesting that high silt soils may have the greatest potential for NH volatilization.

A modeling study of the influence of initial soil moisture on summer precipitation during the East Asian summer monsoon

The state-of-the-art WRF model is used to investigate the impact of the antecedent soil moisture on subsequent summer precipitation during the East Asian summer monsoon (EASM) period. The control experiment with realistic soil moisture condition can well reproduce the seasonal pattern from low- to high- atmosphere, as well as the spatial distribution of precipitation belt in East China. Compared with the control experiment, the sensitivity experiment in which the initial soil moisture is reduced generates more precipitation along the East China Sea, and less rainfall over both Central and South China. This suggests that the effect of initial soil moisture on monsoonal precipitation in East China is regionally dependent. The influence on precipitation is mostly attributed to the change in precipitation from mid July to late August. The initial soil moisture condition plays a role in changing the seasonal pattern and atmospheric circulation due to the weak heating and geopotential gradient, leading to a reduction in southeasterly flow and moisture flux from South China Sea. The changes between DRY and CTL runs result in reduced southerly wind over the ocean (south of ˜25 °N) and enhanced northerly wind over the land (north of ∼25 °N). The temperature and associated circulation changes due to drier initial soil moisture anomaly result in reduced southerly winds over East China, and therefore a weakened EASM system. The averaged moisture flux decreases significantly over Central China but increases along the East China Sea. In addition, the drier soil moisture perturbation exerts an effect on suppressing (enhancing) vertical velocity over Central China (along the East China Sea), thus leading to more (less) cloud water and rain water. Therefore, the influence of soil moisture exerts an opposite impact on surface precipitation between these two regions, with more and less accumulation rainfall in Central China and along the East China Sea, respectively.

Natural dam breaching due to overtopping: effects of initial soil moisture

Natural dams formed by landslides may produce disastrous floods after dam outbursts. How the breaching characteristics of natural dams are affected by initial soil moisture has remained insufficiently understood. In this paper, we present the results of a series of laboratory tests that assessed five different initial soil moistures (0.3, 2.4, 4.2, 7.3, and 10.3%). Under the present experimental conditions with dams composed of gravel–sand–clay mixtures, the failure of natural dams was primarily caused by the erosion of overtopping flow, and lateral mass collapse also caused breach widening. According to the test results, three stages of the breaching process of natural dams made of different initial soil moistures were observed. The results show that peak discharge increased with the increase in the initial soil moisture, while the breaching time and height of the residual dam decreased. In the process of the breach, the backward erosion was weakened gradually with the increase in the initial soil moisture. When the initial soil moisture increased, the breach deepened faster than it widened, and the ratio of the breaching width to depth after dam outburst tended to be greater than 1 at first and then less than 1. A function of the breaching width and depth is established, making it possible to calculate both variables. This function is based on a shape parameter that linearly decreases with initial soil moisture.

Effects of Rain Intensity and Initial Soil Moisture on Hydrological Responses in Laboratory Conditions

Abstract Although the possibility of measuring and analysing all parts of the rainfall, infiltration, runoff, and erosion process as a natural hydrologic cycle in field conditions is still one of the more unattainable goals in the hydrological sciences, it can be accomplished in laboratory conditions as a way to understand the whole process. The initial moisture content is one of the most effective factors on soil infiltration, runoff, and erosion responses. The present research was conducted on a 2 m2 laboratory plot at a slope of 9% on a typical sandy-loam soil. The effects of the initial soil moisture content on the infiltration, runoff, and erosion processes were studied at four levels of initial soil moisture content (12, 25, 33, and 40 volumetric percentage) and two rainfall intensities (60 and 120 mm h-1). The results showed a significant (p ≤ 0.05) correlation between rainfall intensity and downstream splash, with r = 0.87. The results reflected the theory of hydrological responses, showing significant (p ≤ 0.05) correlations with r =-0.93, 0.98, -0.83, 0.88, and 0.73 between the initial soil moisture content and the time-to-runoff, runoff coefficient, drainage as a part of the infiltrated water, downstream splash, and total outflow sediment, respectively.

Modeling effect of initial soil moisture on sorptivity and infiltration

[1] A soil's capillarity, associated with the parameter sorptivity, is a dominant control on infiltration, particularly at the onset of rainfall or irrigation. Many mathematical models used to estimate sorptivity are only valid for dry soils. This paper examines how sorptivity and its capillary component (as wetting front potential) change with initial degree of saturation. We capture these effects with a simple modification to the classic Green-Ampt model of sorptivity. The modified model has practical applications, including (1) accurately describing the relative sorptivity of a soil at various water contents and (2) allowing for quantification of a soil's saturated hydraulic conductivity from sorptivity measurements, given estimates of the soil's characteristic curve and initial water content. The latter application is particularly useful in soils of low permeability, where the time required to estimate hydraulic conductivity through steady-state methods can be impractical.

Soil moisture influences the development of Haemonchus contortus and Trichostrongylus colubriformis to third stage larvae

Two climate chamber experiments were conducted to determine the effect of varying initial soil moisture (0, 10 and 15%), simulated rainfall amount (0, 12 and 24mm) and simulated rainfall timing (days −1, 0 and 3 relative to faecal deposition) on development (day 14) of Haemonchus contortus and Trichostrongylus colubriformis to the third stage larvae (L3) and faecal moisture (FM). Increasing initial soil moisture content from 0 to 10 or 15% led to higher recovery of total L3 (P<0.001). Total L3 recovery increased with each level of simulated rainfall (P<0.001) in the ascending order of 0, 12 and 24mm. There was an interaction between the effects of initial soil moisture and simulated rainfall amount on the recovery of total L3, showing that the benefit of increased simulated rainfall lessened with increasing soil moisture. Simulated rainfall on the day of deposition resulted in higher recovery of L3 (P<0.001) than simulated rainfall on other days. FM on day 3 relative to faecal deposition was best associated with recovery of total H. contortus and T. colubriformis L3 (R2=0.32–0.46), reinforcing the importance of sufficient moisture soon after faecal deposition. The effects of initial soil moisture, and the amount and timing of simulated rainfall on development to L3 were largely explained by changes to FM and soil moisture values within 4 days relative to faecal deposition. These results highlight the influence of soil moisture and its interaction with rainfall on development of H. contortus and T. colubriformis to L3. Consequently we recommend that soil moisture be given greater importance and definition in the conduct of ecological studies of parasitic nematodes, in order to improve predictions of development to L3.

Effects of Initial Soil Moisture on Rainfall Generation and Subsequent Hydrologic Response during the North American Monsoon

Abstract Through the use of a mesoscale meteorological model and distributed hydrologic model, the effects of initial soil moisture on rainfall generation, streamflow, and evapotranspiration during the North American monsoon are examined. A collection of atmospheric fields is simulated by varying initial soil moisture in the meteorological model. Analysis of the simulated rainfall fields shows that the total rainfall, intensity, and spatial coverage increase with higher soil moisture. Hydrologic simulations forced by the meteorological fields are performed using two scenarios: (i) fixed soil moisture initializations obtained via a drainage experiment in the hydrologic model and (ii) adjusted initializations to match conditions in the two models. The scenarios indicate that the runoff ratio increases with higher rainfall, although a change is observed from a linear (fixed initialization) to a nonlinear response (adjusted initialization). Variations in basin response are attributed to controls exerted by rainfall, soil, and vegetation properties for varying initial conditions. Antecedent wetness significantly influences the runoff response through the interplay of different runoff generation mechanisms and also controls the evapotranspiration process. The authors conclude that a regional increase in initial soil moisture promotes rainfall generation, streamflow, and evapotranspiration for this warm-season case study.

Time‐lagged effects of spring Tibetan Plateau soil moisture on the monsoon over China in early summer

AbstractThe objective of the present study is to investigate the effect of initial soil moisture in the Tibetan Plateau (ISMTP) during the spring period on the local and regional climate in subsequent months. Numerical experiments with different ISMTP are made from 1 April to 30 June for the year 1998 using a regional climate model. This was a wet year with anomalously high summer precipitation over China. The same experiments have also been done for the year 1995, which was a normal year with respect to the summer rainfall over China. In both years, the snow amount over the Tibetan Plateau (TP) was higher than normal in the preceding winter/spring. The results of the experiments indicated that an increase in the ISMTP may lead to decreases in the air temperature, vertical velocity, and surface heating over the TP in June. In addition to the local effects, an increase in the ISMTP may also lead to modifications of the climate in some remote regions in early summer, such as an increase in the amount of monsoon precipitation over the mid to lower reaches of the Yangtze River region in eastern China and a decrease over the south China region. These precipitation differences due to the changes in ISMTP are consistent with those due to anomalous snow cover over the TP in winter or spring. Physically, the Tibetan High is weakened with an increase in ISMTP, which leads to a change in the strength of the Asian summer monsoon. Copyright © 2007 Royal Meteorological Society

A large-eddy simulation study of cumulus clouds over land and sensitivity to soil moisture

A series of large-eddy simulations (LES) of non-precipitating cumulus clouds over land was performed. These simulations were idealized from observed conditions at the Southern Great Plains ARM site on 21 June 1997 and were intended to investigate the effect of initial soil moisture on the structure of the cloudy boundary layer. The surface fluxes were either dominated by latent heat or sensible heat flux, with the transition between one regime and the other occurring over a very narrow soil moisture range. The effect on clouds was mixed. Cloud fraction was nearly identical throughout all experiments. Simulations with dominant sensible heat fluxes led to more turbulent boundary layers and higher cloud bases. Simulations dominated by latent heat flux tended to have fewer but stronger updrafts in the cloud layer.

Dynamics of nematodes and protozoa following the experimental addition of cattle or pig slurry to soil

An experimental system was used in which slurry could be placed in the central section of a tube, between two cores of packed, sieved soil. The system simulated the direct injection of slurry into soil and there was movement of water and substrate from the slurry into the surrounding soil. The effects of initial soil moisture, soil nitrate concentration and slurry type, on communities of nematodes and protozoa in soil sections adjacent to and away from the slurry were investigated. Protozoa increased rapidly in the soil layer adjacent to the slurry, but responded more quickly following the addition of pig slurry than cattle slurry. Pig slurry also specifically stimulated ciliates, especially larger Hypotrich ciliates. Nematodes, however, were stimulated to a greater extent by cattle than pig slurry. It is argued that pig slurry contained a greater proportion of readily-available C than cattle slurry. There was also a substantial increase in nematode numbers in soil up to 12 cm from the slurry. This was attributed to the migration of nematodes away from the soil section adjacent to the slurry. A separate experiment was conducted with gel-stabilised cattle slurry, which restricted the movement of water and substrate from the slurry. In this case there was no stimulation of microfauna in soil more than 2 mm from the soil-slurry interface, the largest changes occurred within the slurry phase.

Numerical experiments of the effects of initial desert moisture on the climate change

A numerical model with thep-sigma incorporated coordinate system and primitive equations is used to simulate the effect of initial soil moisture in desert areas on the climate change. The results show that the present deserts have a tendency to expand. When the initial soil moisture in the desert regions increases, the desert areas will shrink but can not disappear. The small deserts may not remain any longer when there are sources of water vapour around. Both the land-sea contrast and the topography are the background conditions of the present desert distribution through the mechanism of the downdrafts and the rare precipitation over the desert regions. The increase of the initial desert soil moisture will weaken the summer monsoon circulation and, consequently, the monsoonal precipitation.

The infiltration envelope: Results from a theoretical infiltrometer

The theoretical partial differential equation for unsaturated soil moisture flow is solved by a versatile numerical scheme designed for accurate simulation of infiltration from various patterns of rainfall. This model is used to study the independent effects of soil type, initial soil moisture, rainfall rate and rainfall pattern. The results of the investigation are expressable as a simple parametric model for vertical infiltration. Infiltration from a suddenly ponded surface is shown to be an asymptotic limit to increasing rainfall rates. A single dimensionless formula is found to accurately describe the infiltration decay curves for all soils, initial conditions, and rainfall rates tested, and another dimensionless relation predicts time to ponding under arbitrary rainfall patterns as a function of infiltrated rainfall depth. The effect of initial soil moisture is shown to be well described by a simple linear effect on the normalizing time in the dimensionless system. Uses and implications of these results are discussed.