Seasonal Moisture Variations Research Articles

A sub-pixel method for estimating planting fraction of paddy rice in Northeast China

Timely and accurate data regarding the distribution of paddy rice are valuable for various agricultural studies. In this study, we aimed to develop a sub-pixel method for estimating the planting fraction of paddy rice in Northeast China. This method assumes low seasonal variations in moisture in paddy rice fields compared with other upland crops due to the presence of flooding water throughout the growing season. We used the coefficient of variation (CV) of the land surface water index (LSWI) derived from the moderate resolution imaging spectroradiometer (MODIS) to indicate the water condition. High resolution images obtained by an unmanned aerial vehicle (UAV) were used to test this assumption and to develop the relationship between the CV of LSWI and the planting fraction of paddy rice. The results showed that the CV of LSWI could effectively indicate the planting fraction of paddy rice, where our method explained 84% of the variation in the planting fraction of paddy rice in the UAV survey sites. Validation based on the statistical data showed that this method explained 78% and 85% of the variations in the paddy rice area at the county and prefecture levels, respectively. Moreover, the performance of this method was good independent of the field survey data, and this alternative approach may facilitate mapping of the planting distribution of paddy rice over large areas.

Determination of the Characteristic Values and Variation Ratio for Sensitive Soils

In 2008, Romania adopted Eurocode 7, part II, regarding the geotechnical investigations – called SR EN1997-2/2008. However a previous standard already existed in Romania, by using the mathematical statistics in determination of the calculation values, the requirements of Eurocode can be taken into consideration. The setting of characteristics and calculations values of the geotechnical parameters was finally issued in Romania at the end of 2010 at standard NP122-2010 – “Norm regarding determination of the characteristic and calculation values of the geotechnical parameters”. This standard allows using of data already known from analysed area and setting the calculation values of geotechnical parameters. However, this possibility exist, it is not performed easy in Romania, considering that there isn’t any centralized system of information coming from the geotechnical studies performed for various objectives of private or national interests. Every company performing geotechnical studies tries to organize its own data base, but unfortunately none of them use existing centralized data. When determining the values of calculation, an important role is played by the variation ratio of the characteristic values of a geotechnical parameter. There are recommendations in the mentioned Norm, that could be taken into account, regarding the limits of the variation ratio, but these values are mentioned for Quaternary age soils only, normally consolidated, with a content of organic material < 5%. All of the difficult soils are excluded from the Norm even if they exist and affect the construction foundations on more than a half of the Romania’s surface. A type of difficult soil, extremely widespread on the Romania’s territory, is the contractile soil (with high swelling and contractions, very sensitive to the seasonal moisture variations). This type of material covers and influences the construction foundations in one over third of Romania’s territory. This work is proposing to be a step in determination of limits of the variation ratios for the contractile soils category, for the most used geotechnical parameters in the Romanian engineering practice, namely: the index of consistency and the cohesion.

Effect of Moisture Hysteresis on the Resilient Modulus of Lime-Treated Expansive Clay

Abstract Several studies have asserted that seasonal moisture variation of unsaturated subgrade has a significant impact on its resilient modulus and, consequently, on the pavement performance and longevity. In regard to unsaturated lime-treated expansive subgrade, little research has addressed the influence of moisture variation on resilient modulus (MR). In this context, this study aims at evaluating the effect of the drying and wetting cycle on the resilient behavior of lime-treated expansive clay at optimum lime conditions. Initially, the effects of lime content and curing period on the MR of lime-treated expansive clay were investigated to evaluate the optimum lime content. This involved conducting a series of repeated load tests under different lime contents and curing periods. In addition, a complementary series of tests were conducted to evaluate the unconfined compression strength along the same drying and wetting paths. Test data indicated that lime treatment resulted in a 370 % increase in the MR after 28 days curing. On the other hand, the effect of the wetting and drying cycle, depicted as the relationship between MR and suction (or water content), showed a hysteresis phenomenon. Further examination of the MR along the drying path indicated a positive contribution of suction to the resilient behavior of lime-treated samples up to a specific suction value (&amp;gt;20 MPa), after which this contribution is considered negligible. Hysteresis phenomenon was also observed for unconfined compression strength because of wetting and drying; however, with a different trend. The discrepancy between hysteresis trends were attributed to differences in loading characteristics.

Instrumentation for Monitoring Pavement Performance in Cold Regions

AbstractThe mechanistic–empirical (ME) design guide developed under the National Cooperative Highway Research Program represents a true change in the approach to engineering road structures. Changes in material properties with seasonal variations in moisture and temperature condition, which influence the mechanical response of the materials and hence the structural response of road layers, forced reliance on empirical measures to predict performance. These empirical functions will require calibration to ensure the prediction model is responsive to local conditions including adopted construction practice. The performance of pavements in cold regions clearly reveal the need to properly measure the distribution of stresses, strains, moisture, and thermal regimes, within road layers over a period of time. This paper presents the design, implementation, and use of a practical road instrumentation monitoring system capable of capturing all structural and environmental data for roadways. This proposed road insta...

Soil Resilient Modulus Regressed from Physical Properties and Influence of Seasonal Variation on Asphalt Pavement Performance

Subgrade soil, as the critical underlying support for other pavement layers and traffic loads, should be stiff enough to maintain the integrity of pavement structures and the smoothness of pavement surface. The resilient modulus, as an indicator of subgrade stiffness, is an essential input in the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical Pavement Design Guide (MEPDG). At input level 1 of MEPDG, the MEPDG generalized model is required to describe resilient modulus of subgrade soil, and the coefficients of this model are used for pavement design. The change of the resilient modulus model has raised the interest of many state highway agencies and made it necessary to convert old resilient modulus test data into new ones required for the MEPDG model. In this study, the coefficients of the generalized and the universal models for soil resilient modulus were obtained through regression of the results of 13 soils in Tennessee. The coefficients of the two models were also compared. There is a potential risk that the coefficients from the universal model may be mistakenly used in the MEPDG instead of those coefficients from the generalized model. The consequence of this improper use was demonstrated in the comparison between the miscalculated and the real resilient moduli. The coefficients of the generalized model were correlated to soil physical properties, which provided an alternate time-saving and economical method to obtain soil resilient modulus as level 2 inputs. The coefficients were obtained at different post-compaction water contents, to allow the estimation of pavement response under seasonal moisture variation of subgrade. Rutting and roughness of two typical pavement sections were analyzed to investigate the influence of the seasonal variation of soil resilient modulus on pavement performance. The results showed that moisture variation had a significant effect on subgrade resilient modulus and, subsequently, on pavement performance. It is recommended that seasonal change in soil resilient modulus be considered in the analysis on pavement performance.

Autogenic Microbial Genesis of Middle Miocene Palustrine Ooids; Nullarbor Plain, Australia

Abstract Miocene palustrine ooids located in the Nullarbor Plain, southern Australia, illustrate the importance of microbes and soil processes in the formation of these spherically laminated grains in pedogenic settings. These particles are composed of dense minimicrite and include a wide assortment of microbially produced structures. Such biogenicity includes interpreted extracellular polymers (EPS), algal filaments, palygorskite and sepiolite nano-fiber mats, bacterial spores, and meniscate fabrics. Ooid nuclei are peloids that are interpreted to have formed via microbial binding of lacustrine sediment in a subsequent palustrine environment, both at the surface and inside underlying karst cavities. The peloids are encapsulated in multigenerational micrite laminations that form the spherical cortex. Individual cortical laminae are made up of degraded minimicrite crystals and complex encrusting mats of palygorskite and sepiolite nano-fibers. Cortex generation is interpreted to have been an annual process involving alternating soil hydration states. In this conceptual model, during the wet season, ooids were covered in bacterial mucus that bound ions from solution and produced hydrated Mg-Si gels that evenly surrounded the entire ooid. Gel dehydration during the following dry season resulted in precipitation of fibrous palygorskite and sepiolite. Succeeding seasonal variations in moisture produced numerous laminae that ultimately resulted in a multigenerational ooid cortex. This annual microbial process provides a new mechanism involving an autogenic formation of ooids that may be applied to a wide variety of pedogenic sediments. Unlike the more common marine ooids that require constant movement to achieve cortical precipitation, the process of grainification, combined with microbially mediated mineral precipitation under different soil hydration states, results in the in-place formation of terrestrial ooids.

Analysis of seven-year moderate resolution imaging spectroradiometer vegetation water indices for drought and fire activity assessment over Georgia of the United States

Using a seven-year history of the satellite measurements and meteorology data over Georgia, USA, this study investigated the capability of a series of satellite-derived vegetation water indices for drought monitoring, as well as the connection between fire occurrence and drought conditions. The vegetation water indices are normalized calculations between MODIS near infrared band 2 and shortwave infrared bands 5, 6, 7, and the difference between bands 6 and 7, denoted by NDWI2,5, NDWI2,6, NDWI2,7 and NMDI, respectively. Results show that the drought conditions indicated by NMDI, NDWI2,6 and NDWI2,7 agree well with what have been identified by meteorology data. NMDI, however, has demonstrated more dependable results regarding seasonal moisture variations, as well as stronger responses to drought conditions than NDWI2,6, and NDWI2,7. The annual fire number exhibits high correspondence to drought conditions. Drought intensity also influenced fire extent and the most widespread fires occurred during the driest years. Analysis reveals that NMDI can be used as an effective indicator for fire risk monitoring. It is expected that this research will greatly benefit many applications, such as monitoring drought and detecting fire danger potential.

TRANSPIRATION AND HYDRAULIC STRATEGIES IN A PIñON–JUNIPER WOODLAND

Anthropogenic climate change is likely to alter the patterns of moisture availability globally. The consequences of these changes on species distributions and ecosystem function are largely unknown, but possibly predictable based on key ecophysiological differences among currently coexisting species. In this study, we examined the environmental and biological controls on transpiration from a piñon-juniper (Pinus edulis-Juniperus osteosperma) woodland in southern Utah, USA. The potential for climate-change-associated shifts in moisture inputs could play a critical role in influencing the relative vulnerabilities of piñons and junipers to drought and affecting management decisions regarding the persistence of this dominant landscape type in the Intermountain West. We aimed to assess the sensitivity of this woodland to seasonal variations in moisture and to mechanistically explain the hydraulic strategies of P. edulis and J. osteosperma through the use of a hydraulic transport model. Transpiration from the woodland was highly sensitive to variations in seasonal moisture inputs. There were two distinct seasonal pulses of transpiration: a reliable spring pulse supplied by winter-derived precipitation, and a highly variable summer pulse supplied by monsoonal precipitation. Transpiration of P. edulis and J. osteosperma was well predicted by a mechanistic hydraulic transport model (R2 = 0.83 and 0.92, respectively). Our hydraulic model indicated that isohydric regulation of water potential in P. edulis minimized xylem cavitation during drought, which facilitated drought recovery (94% of pre-drought water uptake) but came at the cost of cessation of gas exchange for potentially extended periods. In contrast, the anisohydric J. osteosperma was able to maintain gas exchange at lower water potentials than P. edulis but experienced greater cavitation over the drought and showed a lesser degree of post-drought recovery (55% of pre-drought uptake). As a result, these species should be differentially affected by shifts in the frequency, duration, and intensity of drought. Our results highlight the sensitivity of this woodland type to potential climate-change-associated shifts in seasonal moisture patterns and demonstrate the utility of mechanistic hydraulic models in explaining differential responses of coexisting species to drought.

Seasonal variations in moisture use in a piñon–juniper woodland

In water-limited environments of the intermountain region of North America, summer precipitation may play a role in the structure and function of aridland communities and ecosystems. This study examined the potential reliance on summer precipitation of two widespread, coexisting woody species in the southwestern United States, Pinus edulis Englmn. (Colorado piñon) and Juniperus osteosperma (Torr) Little (Utah juniper). The current distributions of P. edulis and J. osteosperma are highly suggestive of different dependencies on summer rainfall. We hypothesized that P. edulis was dependent on summer precipitation, utilizing summer precipitation even during extremely dry summers, whereas J. osteosperma was not dependent, using summer precipitation only when amounts were above some minimum threshold. Using sap flux and stable isotopic methods to assess seasonal water sources and water use efficiency, we examined the response of these two species to seasonal variations in moisture at a site located near the northern limits of the North American monsoon. Both sap flux and isotopic results indicated that P. edulis was responsive to summer rain, while J. osteosperma was not. Following summer rain events, sap flux density increased in P. edulis for several days, but not in J. osteosperma. Isotopic evidence indicated that P. edulis took up summer-derived moisture to a greater extent than J. osteosperma. Values of the natural abundance stable isotope ratio of carbon of leaf soluble carbohydrates increased over the summer for P. edulis, indicative of assimilation at higher water use efficiency, but were invariant for J. osteosperma. Our results supported the hypothesis that P. edulis and J. osteosperma are differentially sensitive to summer precipitation and are discussed in the light of potential changes in the seasonality of precipitation associated with climate change.

Precipitation from vertical motion: a statistical diagnostic scheme

AbstractThe relationship between precipitation and atmospheric vertical motion is investigated over the globe. By combining and averaging precipitation rates within small ranges of vertical motion, the mean precipitation rate is found to vary smoothly with vertical motion. The relationship is modelled with a simple function that assumes zero precipitation for subsidence and linearly increasing precipitation for ascending motion. Function parameters are computed from National Centers for Environmental Prediction reanalysis data individually for every grid point and calendar month. Variations in the slope account for geographical and seasonal variations in moisture and other precipitation factors. At each grid point, the scheme diagnoses precipitation rate from a single concurrent value of vertical motion. It is shown to have moderate skill over climatology in predicting mean monthly precipitation. The midlatitudes, oceans and the winter season are favoured. The scheme is designed to extract precipitation fields from a dry general circulation model, based on the simulated vertical motion. Application to climate modelling is discussed. Copyright © 2003 Royal Meteorological Society

Evaluating Moisture Sensors and Monitoring Seasonal Moisture Variation in Low-Volume Roads

For the past several years, the Forest Service of the U.S. Department of Agriculture has been evaluating a quantitative technique for the application and removal of load restrictions by observing relationships among pavement stiffness, pavement damage, soil moisture, and seasonal freezing and thawing. Laboratory tests of time-domain reflectometry (TDR) and radio frequency (RF) sensors showed them to be reasonably accurate and repeatable when compared with known moisture values in several soil types. Laboratory tests of the probes under repeated adverse freezethaw cycling showed the probes to be durable. Although the field survival rate of TDRs surpassed that of RFs, analysis of field data collected at seven locations in four national forests showed that permanently installed sensors strategically located on a forest road network can provide an affordable method for quantitatively determining the beginning and end of critical periods of pavement weakening associated with springthaw. This information would be useful in administering periods of spring-thaw load restrictions. The laboratory and field test programs conducted are outlined. The field technique is applicable to any secondary road subjected to seasonal freezing.

Analyzing ground-water gley and surface-water (pseudogley) effects in paleosols

Sedimentological studies of ancient fluvial systems commonly do not consider in detail palaeosols in floodplain deposits. This is the case of the upper Paleocene Esplugafreda Formation (Pyrenees, Spain), a 100–340 m thick alluvial succession, in which palaeosols represent more than 80% of its thickness. This unit closely predates the climate crisis of the Paleocene/Eocene transition, the PETM (Paleocene/Eocene Thermal Maximum). The purpose of this paper is to define the palaeoenvironmental conditions of formation of these palaeopedogenic conditions, and to establish possible changes during the late Paleocene directly prior to the onset of the PETM. This paper analyses the palaeosols in terms of variations in ‘aquic conditions’, concerning to water saturation, reduction and formation of redoximorphic features in soils.The uppermost part of the Esplugafreda Formation consists of cumulative sandy mudstone palaeosols, laterally associated with sparse channel deposits. Two pedotypes were recognised: Pont d'Orrit and Areny. A mud content >60% (mainly montmorillonite), pedogenic slickensides, wedge-shaped aggregates, mukkara and blow structures indicate that both pedotypes belong to the Vertisol order. They reveal a climate characterised by strong seasonal moisture variations. The Pont d'Orrit pedotype, which dominates the lower portion of the succession, shows reddish brown horizons (Bss), calcareous nodules concentration (Bssk horizon) and scarce redoximorphic features, which indicate a semi-arid climate. The Areny pedotype, which prevails in the upper part, shows a yellow horizon (Bssg) containing goethite and abundant redoximorphic features, which reveal aquic conditions. There is no clear sedimentological evidence that river flooding became relatively more frequent in the upper part of the succession, suggesting that the aquic conditions were caused by an increase in precipitation. This study demonstrates that (i) changes in some pedogenic features within the Vertisols enable interpretation of palaeoenvironmental variations and (ii) this region experienced a changing climate in the late Paleocene, before the onset of the PETM.

Geology of Dallas, Texas, United States of America

Dallas, the seventh largest city in the United States and the second largest city in Texas, lies within the Blackland Prairie physiographic province. The modern city, born on a “hardrock” crossing in the Trinity River in 1845, was also the site of many earlier Indian settlements dating to 11,000 B.C. The city is located on the updip edge of the Gulf Coastal Plain at the northwestern limit of the East Texas Embayment. A wedge of 610–1,372 m of Cretaceous age sedimentary rocks underlies the city. Paleozoic rocks of undetermined thickness are encountered below these units. Surficial deposits include, in ascending order, the Eagle Ford Shale, the Austin Chalk, the Ozan Formation (Taylor Marl) of Cretaceous age, and terraced alluvial deposits of Quaternary age. Soils consist of residual clays and silty clays (CH-CL) over bedrock and transported silty and sandy clays and gravels in terraced alluvial deposits and recent alluvium. Only three major constraints were identified in Dallas: expansive soils and bedrock, slope instability, and flooding. Most damage due to expansive soils is concentrated in areas of lightly loaded structures. Here techniques such as “pre-wetting,” lime stabilization and engineered slabs or pier and beam foundations systems are being utilized. Heavily loaded structures are usually tied into bedrock below the zone of seasonal moisture variation through means of drilled-shaft foundations. Most slope instability and flooding problems are administered through avant-garde hillslope and flood-plain ordinances. Dallas9s water supply is projected to be adequate through the year 2050. While surface water reservoirs are the major source of water, ground water, considered an emergency water source by the city, is being mined by private industry and surrounding municipalities at rates faster than apparent recharge. Solid waste is managed through a 4 km 2 landfill operation and is projected to be adequate for the next 50–75 years. Hazardous waste is transported to the Texas Gulf Coastal depositories.

Nitrogen studies on black soils form the Darling Downs, Queensland. I. Seasonal variations in moisture and mineral nitrogen fractions

A study of the equilibrium levels of moisture, nitrate nitrogen, and ammonium nitrogen is reported on two representative black soils (developed from basaltic colluvium and alluvium respectively) from the Darling Downs for the years 1952-1954 inclusive. Both soils were under native grassland in 1952; a portion of the sampling area at each site was cultivated early in 1953 and left fallow for the rest of the sampling programme. The moisture contents of surface (0-6 in.) grassland and fallow plots varied directly with rainfall. Subsoil under grass showed low moisture contents which increased only after heavy rain but decreased thereafter, probably owing to transpiration. Under fallow, subsoil moisture was higher and showed significant fluctuations, suggesting that losses occurred by slow liquid flow or vapour movement a t moisture contents between field capacity and the wilting point. Ammonia-nitrogen contents at the surface were lower than for comparable soils in temperate regions and showed a significant decrease with depth; values for the corresponding fallow plots were similar in amount and varied similarly with depth. Surface soils showed minor fluctuations with season, being higher in summer. Under incubation conditions at 25°C, ammonia nitrogen rarely fell below 1.0 mg/kg oven-dry soil, which suggests that this is the minimum threshold concentration of ammonia nitrogen in these soils for the nitrification process. Nitrate nitrogen showed a significant rise in summer on the colluvial basaltic soil under grass. The soil developed on basaltic alluvium showed no such seasonal trend and contained uniformly low amounts of this fraction. Cultivation resulted in a sharp rise in nitrate nitrogen in both soils, the wetter alluvial soil showing a longer time lag. There was some evidence of nitrification in the 6-12 in. depth a t one site, but below this rises in nitrate nitrogen, which were correlated with rainfall and increases in moisture content, could be accounted for by leaching. Incubation tests gave rise to highly variable nitrate nitrogen contents and such tests were found unreliable in these soils, probably owing to imperfect aeration of the laboratory sample. Analyses for total nitrogen of several alluvial black soils from the same area showed a progressive decline in this constituent with increasing periods of cultivation; in the first 26 years of cultivation about 0.8 per cent. of the total nitrogen is lost per annum. This value agrees with the nitrate nitrogen accession in fallow subsoil, suggesting that leaching of nitrate formed at the surface is a major factor determining losses in total nitrogen. The implications of these findings are discussed.