Moisture Dependence Research Articles

Energy-saving irrigation management

A significant part of the water resources used in agricultural production comes for irrigation. Due to the strong dependence of soil moisture on weather factors, the irrigation process must be carefully managed. To date, irrigation management is mainly carried out either as a function of soil moisture or according to a predetermined program. The article shows that both methods of management are imperfect since they can lead to a violation of agrotechnical requirements and waste of water. In order to improve the quality of irrigation and eliminate overspending of water resources, it was proposed to manage the water in a combined way. In this case, the formation of the control action occurs according to the results of the comparison of the controlled variable and disturbing influences with the reference values. The controlled value is the soil moisture, and as disturbing influences are considered the temperature and humidity of the air, atmospheric pressure, wind speed, precipitation. In addition, the proposed irrigation management method takes into account the forecast of the synoptic services on precipitation, their intensity and duration. To obtain information on the controlled value, as well as on disturbing influences, appropriate measuring devices are used, and information on the prediction of precipitation is delivered from a specialized server via the Internet. Before starting to use the control method, the agrotechnical requirements, the type, age and vegetation period of the plants are determined and set. The inclusion of irrigation equipment is carried out in accordance with the program and shut down - depending on the magnitude of the control signal.

Comparison of TDR and X-ray method for determining moisture transport parameters

This work compares two methods, the X-ray method and the time domain reflectometry (TDR) method, which are used for determining moisture transport parameters, such as moisture diffusivity, w-λ profile and absorption coefficient. Both methods are suitable for measuring instantaneous moisture content profiles during water transfer through a porous material. However, while the X-ray method is fully non-destructive, the TDR measurement requires installation of TDR probes into the measured material and the obtained results can be influenced by the quality of the contact between the TDR probe and material.The moisture transport parameters were determined from the measured moisture profiles during the process of water uptake, realized on calcium silicate samples. The same measurement arrangement and sample treatment were applied for both methods. The moisture diffusivity moisture dependence was calculated using Boltzmann transformation.The moisture transport parameters obtained by the TDR method were sufficiently close to the values obtained from the X-ray measurement.

Influence of moisture dependency of pressboard on transformer winding clamping pressure

Short circuit (SC) strength of a power transformer is influenced by its winding clamping pressure. The required level of clamping pressure is selected at the design stage based on the maximum allowable SC current level of the transformer. Progressive loss of clamping pressure is a common problem in power transformers. Shrinkage and fading of the stiffness of solid insulation due to thermal degradation are the most common causes of this problem. It has also been identified that changes in the moisture content and repetitive compression cycles on pressboard during high current faults tend to change the winding clamping pressure. This study aims to investigate the effects of moisture and compression cycles on winding clamping pressure through a set of laboratory experiments and finite element analyses. Thickness change and compressive stress-strain curves of pressboard were measured under different moisture conditions. The results were then used to calculate changes in winding geometry and clamping pressure of a 100 kVA three phase, disc type transformer winding.

Large-scale vegetation responses to terrestrial moisture storage changes

Abstract. The normalised difference vegetation index (NDVI) is a useful tool for studying vegetation activity and ecosystem performance at a large spatial scale. In this study we use the Gravity Recovery and Climate Experiment (GRACE) total water storage (TWS) estimates to examine temporal variability of the NDVI across Australia. We aim to demonstrate a new method that reveals the moisture dependence of vegetation cover at different temporal resolutions. Time series of monthly GRACE TWS anomalies are decomposed into different temporal frequencies using a discrete wavelet transform and analysed against time series of the NDVI anomalies in a stepwise regression. The results show that combinations of different frequencies of decomposed GRACE TWS data explain NDVI temporal variations better than raw GRACE TWS alone. Generally, the NDVI appears to be more sensitive to interannual changes in water storage than shorter changes, though grassland-dominated areas are sensitive to higher-frequencies of water-storage changes. Different types of vegetation, defined by areas of land use type, show distinct differences in how they respond to the changes in water storage, which is generally consistent with our physical understanding. This unique method provides useful insight into how the NDVI is affected by changes in water storage at different temporal scales across land use types.

Historical climate controls soil respiration responses to current soil moisture

Ecosystem carbon losses from soil microbial respiration are a key component of global carbon cycling, resulting in the transfer of 40-70 Pg carbon from soil to the atmosphere each year. Because these microbial processes can feed back to climate change, understanding respiration responses to environmental factors is necessary for improved projections. We focus on respiration responses to soil moisture, which remain unresolved in ecosystem models. A common assumption of large-scale models is that soil microorganisms respond to moisture in the same way, regardless of location or climate. Here, we show that soil respiration is constrained by historical climate. We find that historical rainfall controls both the moisture dependence and sensitivity of respiration. Moisture sensitivity, defined as the slope of respiration vs. moisture, increased fourfold across a 480-mm rainfall gradient, resulting in twofold greater carbon loss on average in historically wetter soils compared with historically drier soils. The respiration-moisture relationship was resistant to environmental change in field common gardens and field rainfall manipulations, supporting a persistent effect of historical climate on microbial respiration. Based on these results, predicting future carbon cycling with climate change will require an understanding of the spatial variation and temporal lags in microbial responses created by historical rainfall.

Applying fractal analysis to detect spatio-temporal variability of soil moisture content on two contrasting land use hillslopes

Soil moisture variations in space and time are critical in ecological, hydrological, pedological and environmental studies. This study used fractal analysis to detect the spatio-temporal variability of soil moisture on two contrasting land use hillslopes in the hilly area of Taihu Lake Basin of China. Surface (0–20cm) soil moisture data from January 2013 to September 2015 (a total of 37 sampling days) were analyzed at 39 and 38 sites on the tea garden and forest hillslopes, respectively, with a spatial resolution of about 8m. Results showed that the forest hillslope was significantly (P<0.05) wetter than the tea garden hillslope. The spatial mean soil moisture on both hillslopes had a significant negative linear correlation (R2=0.753 for tea garden (P<0.05) and R2=0.459 for forest (P<0.05)) with corresponding CV for 37 sampling dates. The fractal dimension (D) was found to be better than the nugget/sill ratio in describing the spatial dependence of soil moisture. The advantage of the D is that it does not require the modelling of the semivariogram since it can be calculated on the basis of the experimental semivariogram. Soil moisture on the forest hillslope showed stronger spatial dependence than that on the tea garden hillslope according to D. However, the soil moisture on both hillslopes showed similar temporal dependence and a low-to-moderate autocorrelation structure. In addition, the temporal variability of soil moisture content was spatially correlated on tea garden hillslope. If a location is temporally autocorrelated, the locations nearby tend also to be temporally autocorrelated. It would be possible to make more accurate moisture trend predictions for temporal autocorrelated locations with small D. These findings had important applications related to sampling design, simulation of soil water flow and agricultural water resources management.

The dendroecological potential of shrubs in north Iranian semi-deserts

In deserts and semi-deserts such as in the Irano-Turanian region in northern Iran, forest vegetation is scarce but shrubs are dominant. For this floristic province, placed in a biodiversity hotspot with a cold and dry climate, we provide the first climate-growth study on shrubs. From stems of three wide-spread shrubs (Astragalus, Rhamnus and Ephedra species) annual rings were identified and their widths measured.On average, around 40-year long annual-ring series per stem were obtained, cross-dated and related to meteorological variables. Astragalus and Rhamnus reflected a clear regional climate signal in their ring widths whereas Ephedra showed an only weak association with climate variables. While above-average air humidity in combination with low temperatures in spring and summer favored shrub growth, precipitation had surprisingly only a weak effect on growth. From the abundance of fog events in this area, we concluded that the extreme moisture dependency of the shrubs before and throughout the growing season may have been relieved by the uptake of fog drip through the foliage.As projected by climate models, the deficit in humidity will intensify and temperature will continue to rise in this region. So, the ability of the Irano-Turanian endemic shrubs to infiltrate into neighboring regions could become limited and their current distribution range may be confined to higher elevations which provide a moister and cooler environment.

Influence of moisture content on mode I fracture process of Pinus pinaster: evolution of micro-cracking and crack-bridging energies highlighted by bilinear softening in cohesive zone model

This paper is dedicated to the study of the effect of moisture content on fracture properties of wood through the corresponding effect on the softening function used in cohesive zone model to describe quasi-brittle failure of wood. Bi-linear softening parameters of cohesive zone model are estimated from equivalent linear elastic fracture mechanics resistance curve obtained from a significant number of fracture tests performed in mode I for a wide range of moisture contents (from 5 to $$30\%$$ moisture). The evolution of the cohesive zone parameters as a function of the moisture exhibits a moisture dependence of the fracture properties of wood and especially the increase of the cohesive energy related to the crack-bridging phenomenon.

Moisture-dependent orthotropic elasticity and strength properties of Chinese fir wood

Elastic and strength properties are very important material characteristics in mechanical modelling. Due to the anisotropic and hygroscopic nature of wood, a characterization of wood mechanical behavior will require knowledge of its moisture-dependent properties in relation to the three principal axes of anisotropy. The influence of moisture content (MC) on the elastic and strength anisotropy of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) wood was examined in the present study. Selected parameters, including the anisotropic Young’s moduli, shear moduli, Poisson’s ratios, yield and ultimate stress values in the longitudinal, radial and tangential directions, were determined in compression and tension tests at different moisture conditions. The results indicated that a distinct moisture dependency is exhibited for the elastic and strength behavior of Chinese fir wood. With the exception of some Poisson’s ratios, all investigated elastic and strength parameters were shown to decrease with increasing MC, whereby individual moduli and strength values were affected by the MC to different degrees. The two- and three-dimensional representation of the compliance matrix and the two-dimensional visualization of a yield surface give a valuable overview on the moisture-dependent elastic and strength anisotropy of Chinese fir wood.

Methodology to evaluate performance of pavement structure using soil moisture profile

Variation of moisture content in the subgrade layer of a flexible pavement may play a significant role in its structural performance by influencing the stiffness of the pavement system. The objective of this study is to develop and test methodologies to incorporate the soil moisture profile into flexible pavement evaluation and to determine how the changes of water table level will affect the pavement deformation. Falling weight deflectometer (FWD) data at two locations in Minnesota and Oklahoma were used to estimate the in situ measured pavement deformation with seasonal changes of water content. Then, a layer elastic analysis approach was adjusted to include the moisture dependency of the subgrade resilient modulus in calculating the deflection basin. The controlling parameters in these set of analyses were asphalt layer temperature, the degree of water saturation in unbound materials, depth to the groundwater table, and depth to bedrock. The environmental data for this study were obtained from the Long Term Pavement Performance-Seasonal Monitoring Program (LTPP-SMP) for the two pavement sections for different climatic conditions. The comparisons showed that dividing the subgrade layer into sublayers with variable, moisture-dependent modulus according to the location of moisture measurements will result in more accurate estimation of the pavement deflection. In addition, the predicted deflections indicated that considering moisture data up to the depth associated with 10% of surface vertical stress may suffice for this type of analysis. However, the overall quality of prediction is sensitive to the material type in the subgrade layer.

The impact of salinity on the microbial response to drying and rewetting in soil

In saline soils, the severity of drought for the soil microbial community is exacerbated by accumulating concentrations of salts during drying. In this study we investigated how bacterial growth and respiration responses to drying-rewetting were affected by salinity. To do this, we adjusted a non-saline soil to four different salinities (0, 2, 7 and 22 mg NaCl g−1), followed by addition of plant material and a one-month incubation. Following the incubation period, we assessed the moisture dependence of respiration and growth, as well as the responses of bacterial growth and respiration to a cycle of air-drying followed by rewetting to optimal moisture. The inhibition of bacterial growth and respiration by reducing moisture increased with higher salt concentrations. As such, salinity was shown to increase the negative impact of drying on bacterial growth and alter the bacterial growth and respiration dynamics after rewetting. Drying-rewetting of soils with low salinity resulted in an immediate onset and gradual resuscitation of bacterial growth to levels similar to before drying. In contrast, in soils with higher salinity growth increased exponentially after a lag period of several hours. The duration of the lag period induced by salinity increased with the amount of salt added. The observed lag period matched previously reported results observed in response to more severe drying by e.g. longer duration of drought and drought combined with starvation. In treatments with a salt concentration ≤7 mg NaCl g−1 a high respiration pulse occurred immediately after rewetting and subsequently respiration declined. In the most saline treatment the initial respiration was reduced below the level of continuously moist soil to later increase exponentially in parallel with the increase in bacterial growth. We conclude that soil salinity increases the inhibition of microbial activity by low moisture, that fundamentally different responses to drying-rewetting cycles can be induced, and that high salt concentrations can substantially delay the pulse of respiration induced by rewetting dry soil.

Ecosystem nitrogen fixation throughout the snow-free period in subarctic tundra: effects of willow and birch litter addition and warming.

Nitrogen (N) fixation in moss-associated cyanobacteria is one of the main sources of available N for N-limited ecosystems such as subarctic tundra. Yet, N2 fixation in mosses is strongly influenced by soil moisture and temperature. Thus, temporal scaling up of low-frequency insitu measurements to several weeks, months or even the entire growing season without taking into account changes in abiotic conditions cannot capture the variation in moss-associated N2 fixation. We therefore aimed to estimate moss-associated N2 fixation throughout the snow-free period in subarctic tundra in field experiments simulating climate change: willow (Salix myrsinifolia) and birch (Betula pubescens spp. tortuosa) litter addition, and warming. To achieve this, we established relationships between measured insitu N2 fixation rates and soil moisture and soil temperature and used high-resolution measurements of soil moisture and soil temperature (hourly from May to October) to model N2 fixation. The modelled N2 fixation rates were highest in the warmed (2.8±0.3kg N ha-1 ) and birch litter addition plots (2.8±0.2kg N ha-1 ), and lowest in the plots receiving willow litter (1.6±0.2kg N ha-1 ). The control plots had intermediate rates (2.2±0.2kg N ha-1 ). Further, N2 fixation was highest during the summer in the warmed plots, but was lowest in the litter addition plots during the same period. The temperature and moisture dependence of N2 fixation was different between the climate change treatments, indicating a shift in the N2 fixer community. Our findings, using a combined empirical and modelling approach, suggest that a longer snow-free period and increased temperatures in a future climate will likely lead to higher N2 fixation rates in mosses. Yet, the consequences of increased litter fall on moss-associated N2 fixation due to shrub expansion in the Arctic will depend on the shrub species' litter traits.

Hygrothermal behavior of a CFRR-metal adhesively bonded joint with coupled transfer of heat and moisture through the thickness

The coupled heat and moisture transfer and the induced hygrothermal stress in a carbon fiber reinforced resin (CFRR)-metal adhesively bonded joint is investigated theoretically in this article. The adhesive joint is treated as a three-layer narrow plate and the whole problem is simplified to be one-dimensional along the thickness. Temperature and moisture dependencies of the resin matrix in CFRR as well as the adhesive material properties are taken into account. The Luikov’s equations for heat and mass transfer are applied to build the coupling diffusion system of heat and moisture. The differential quadrature method (DQM) is used in space domain and the Runge–Kutta method used in time domain to achieve the numerical results of temperature and moisture fields as well as the induced hygrothermal stress distributions. Investigations in this paper may offer theoretical references to studies of adhesively bonded structures of dissimilar materials operating in complex environment conditions.

Copolarized and Cross-Polarized Backscattering From Random Rough Soil Surfaces From L-Band to Ku-Band Using Numerical Solutions of Maxwell's Equations With Near-Field Precondition

We extend the 3-D numerical method of Maxwell's equation (NMM3D) for rough soil surface scattering from L-band to C-, X-, and Ku-bands. We illustrate the results for copolarization, cross-polarization, and polarization ratio (HH/VV). Copolarized and cross-polarized backscattering coefficients from NMM3D are analyzed for frequency dependence, incident angle dependence, and soil moisture dependence. We also cross compare results from analytical and empirical models. The 16 $\times$ 16 squared wavelength $(\lambda^2)$ of rough surface is applied for NMM3D using 256 processors on NSF Extreme Science and Engineering Discovery Environment clusters. Polarization ratio, HH/VV, is studied to address the feature of dependence on frequency for same fields (same physical parameters for the model). HH/VV is shown useful to provide additional information to study land surface. Results from NMM3D are also validated with POLARSCAT measurement data-1. NMM3D shows good agreement with data and better performance while considering copolarization, cross-polarization, and polarization ratio (HH/VV) together. The key advancement in computation efficiency in this paper is the implementation of a physically based near-field precondition algorithm in NMM3D to accelerate parallel computation. With precondition, the computation time is faster by ten times for larger root-mean-square height.

Impact of scaling to the resistive switching effect in organic polymer – based structures

AbstractThe resistive switching effect has been studied in a set of organic polymer - based structures of a different composition and size scale from macro to micro. It is shown that scaling down reduces both the threshold switching voltage Vth and the respective effective electric field Eth. Furthermore, introduction of metal micro particles into a macro scale polymer matrix provides the same effect. Therefore the metal particle incorporation may be regarded as an alternative method of effective scaling, depending on an application. Switching speed of less than 15 ns, threshold voltage Vth ~ (2 – 25) V, 105 cycle endurance, no significant moisture dependence and high retention time 3.5 months for scaled down samples aswell as for metal doped macro samples have been demonstrated. These characteristics are suitable for constructing memory devices. The switching effect mechanisms are discussed.

Biofilm as a redox conductor: a systematic study of the moisture and temperature dependence of its electrical properties.

Some microbial biofilms are electrically conductive. However, the mechanism of electron transport remains unclear. Here, we show that μm-scale long-distance electron transport through electrode-grown Geobacter sulfurreducens biofilms occurs via redox conduction, as determined by electrical measurements performed under varied hydration states and temperatures.

Impacts of grid resolution on surface energy fluxes simulated with an integrated surface-groundwater flow model

Abstract. The hydrological component of the Terrestrial Systems Modeling Platform (TerrSysMP), which includes integrated surface-groundwater flow, was used to investigate the grid resolution dependence of simulated soil moisture, soil temperature, and surface energy fluxes over a sub-catchment of the Rur, Germany. The investigation was motivated by the recent developments of new earth system models, which include 3-D physically based groundwater models for the coupling of land–atmosphere interaction and subsurface hydrodynamics. Our findings suggest that for grid resolutions between 100 and 1000 m, the non-local controls of soil moisture are highly grid resolution dependent. Local vegetation, however, strongly modulates the scaling behavior, especially for surface fluxes and soil temperature, which depends on the radiative transfer property of the canopy. This study also shows that for grid resolutions above a few 100 m, the variation of spatial and temporal patterns of sensible and latent heat fluxes may significantly affect the resulting atmospheric mesoscale circulation and boundary layer evolution in coupled runs.

Modelling stomatal conductance of wheat: An assessment of response relationships under elevated CO2

This study proposes Jarvis-type model parameterisations for estimating stomatal conductance (gs) in wheat (Triticum aestivum L.) under ambient [CO2] (a[CO2], approximately 390μmolmol−1) and elevated [CO2] (e[CO2], approximately 550μmolmol−1), based on measurements collected in the Australian Grains Free Air CO2 Enrichment (AGFACE) facility. Relationships of gs with phenological and environmental factors were evaluated using a boundary line technique. Results suggest that gs-response functions for vapour pressure deficit (VPD), volumetric soil moisture (VSM) and temperature dependence were different between a[CO2] and e[CO2]: VPD induced stomatal closure at approximately 3 and 2.5kPa under a[CO2] and e[CO2] respectively, and optimum temperature was 2°C lower under e[CO2]. Elevated [CO2] decreased maximum gs (gmax) by approximately 35%.

Relationships between photosynthesis and formaldehyde as a probe of isoprene emission

Abstract. Atmospheric oxidation of isoprene emission from land plants affects radiative forcing of global climate change. There is an urgent need to understand the factors that control isoprene emission variability on large spatiotemporal scales but such direct observations of isoprene emission do not exist. Two readily available global-scale long-term observation-based data sets hold information about surface isoprene activity: gross primary productivity (GPP) and tropospheric formaldehyde column variability (HCHOv). We analyze multi-year seasonal linear correlations between observed GPP and HCHOv. The observed GPP–HCHOv correlation patterns are used to evaluate a global Earth system model that embeds three alternative leaf-level isoprene emission algorithms. GPP and HCHOv are decoupled in the summertime in the southeast US (r=−0.03). In the Amazon, GPP and HCHOv are weakly correlated in March-April-May (MAM), correlated in June-July-August (JJA) and weakly anticorrelated in September-October-November (SON). Isoprene emission algorithms that include soil moisture dependence demonstrate greater skill in reproducing the observed interannual seasonal GPP–HCHOv correlations in the southeast US and the Amazon. In isoprene emission models that include soil moisture dependence, isoprene emission is correlated with photosynthesis and anticorrelated with HCHOv. In an isoprene emission model without soil moisture dependence, isoprene emission is anticorrelated with photosynthesis and correlated with HCHOv. Long-term monitoring of isoprene emission, soil moisture and meteorology is required in water-limited ecosystems to improve understanding of the factors controlling isoprene emission and its representation in global Earth system models.

The annual cycle of snowfall at Summit, Greenland

AbstractWhile snow accumulation over central Greenland has been extensively studied, interannual variability of snowfall in the region is not well understood due to a dearth of observations. The Integrated Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS) project at Summit, Greenland, offers a unique, ground‐based opportunity to study precipitation in central Greenland where the surface mass balance is positive. Combining data from a Precipitation Occurrence Sensor System (POSS), Millimeter‐wavelength Cloud Radar (MMCR), and snow stake field, the annual cycle of precipitation at Summit is examined. Average daily snowfall is higher by a factor of 3 from June to October compared to November to May, while surface height change is only higher by 15% during the same timeframes. This reduced variability in surface height is explained by the seasonally varying nature of latent heat flux, compaction, and wind contributions. The ICECAPS remote sensors and stake field measurements do not agree as far as total annual water equivalent. This discrepancy is likely due to a low bias in the POSS and MMCR snowfall retrievals for Summit. To further examine the seasonal cycle, snowfall measurements by the POSS were linked to local meteorological parameters, including wind direction, liquid water path (LWP), 2 m temperature, and precipitable water vapor. An observed wind direction and moisture dependence are consistent with snowfall being linked to pulses of moist air that originate over nearby, ice‐free ocean, a resource that becomes more readily available in summertime as the winter sea ice retreats. LWP is shown to have little relationship to snowfall, indicating that ice‐phase precipitation processes are quite important for snowfall at Summit.