scholarly journals Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

2016 ◽  
Vol 20 (8) ◽  
pp. 3099-3108 ◽  
Author(s):  
Tuvia Turkeltaub ◽  
Daniel Kurtzman ◽  
Ofer Dahan
Keyword(s):  
Real Time ◽  
Water Table ◽  
Vadose Zone ◽  
Land Surface ◽  
Agricultural Land ◽  
Root Zone ◽  
Isotopic Signature ◽  
Nitrate Transport ◽  
Mass Migration ◽  
Crop Field

Abstract. Nitrate is considered the most common non-point pollutant in groundwater. It is often attributed to agricultural management, when excess application of nitrogen fertilizer leaches below the root zone and is eventually transported as nitrate through the unsaturated zone to the water table. A lag time of years to decades between processes occurring in the root zone and their final imprint on groundwater quality prevents proper decision-making on land use and groundwater-resource management. This study implemented the vadose-zone monitoring system (VMS) under a commercial crop field. Data obtained by the VMS for 6 years allowed, for the first time known to us, a unique detailed tracking of water percolation and nitrate migration from the surface through the entire vadose zone to the water table at 18.5 m depth. A nitrate concentration time series, which varied with time and depth, revealed – in real time – a major pulse of nitrate mass propagating down through the vadose zone from the root zone toward the water table. Analysis of stable nitrate isotopes indicated that manure is the prevalent source of nitrate in the deep vadose zone and that nitrogen transformation processes have little effect on nitrate isotopic signature. The total nitrogen mass calculations emphasized the nitrate mass migration towards the water table. Furthermore, the simulated pore-water velocity through analytical solution of the convection–dispersion equation shows that nitrate migration time from land surface to groundwater is relatively rapid, approximately 5.9 years. Ultimately, agricultural land uses, which are constrained to high nitrogen application rates and coarse soil texture, are prone to inducing substantial nitrate leaching.

scholarly journals Real-time monitoring of nitrate transport in deep vadose zone under a crop field – implications for groundwater protection

2016 ◽  
Author(s):  
T. Turkeltaub ◽  
D. Kurtzman ◽  
O. Dahan
Keyword(s):  
Real Time ◽  
Water Table ◽  
Vadose Zone ◽  
Root Zone ◽  
Temporal Variations ◽  
Nitrate Transport ◽  
Natural Soil ◽  
Agricultural Field ◽  
Table Analysis ◽  
Concentration Time Series

Abstract. Nitrate is considered the most common non-point pollutant in groundwater. It is often attributed to agricultural management, when excess application of nitrogen fertilizer leaches below the root zone and is eventually transported as nitrate through the unsaturated zone to the water table. A lag time of years to decades between processes occurring in the root zone and their final imprint on groundwater quality prevents proper decision-making on land use and groundwater-resource management. In this study, water flow and solute transport through the deep vadose zone underlying an agricultural field were monitored using a vadose-zone monitoring system (VMS). Data obtained by the VMS over a period of 6 years allowed detailed tracking of water percolation and nitrate migration from the surface through the entire deep vadose zone to the water table at 18 m depth. The temporal variations in the vadose zone sediment water content were used to evaluate the link between rain patterns and water fluxes. A nitrate concentration time series, which varied with time and depth, revealed – in real time – a major pulse of nitrate mass propagating down through the vadose zone from the root zone toward the water table. Analysis of stable nitrate isotopes indicated that manure is the prevalent source of nitrate in the deep vadose zone, and these isotopes were barely affected by natural soil or industrial nitrogen components. Total nitrate mass estimations and simulated pore-water velocity using the analytical solution of the convection–dispersion equation indicated dominance of nitrate vertical transport, and excluded the possibility of lateral nitrate input. Accordingly, prevention of groundwater pollution from surface sources such as agriculture has to include effective and continuous monitoring of the entire vadose zone.

scholarly journals Assimilation of ASCAT near-surface soil moisture into the SIM hydrological model over France

2011 ◽  
Vol 15 (12) ◽  
pp. 3829-3841 ◽  
Author(s):  
C. Draper ◽  
J.-F. Mahfouf ◽  
J.-C. Calvet ◽  
E. Martin ◽  
W. Wagner
Keyword(s):  
Soil Moisture ◽  
Real Time ◽  
Land Surface ◽  
Hydrological Model ◽  
Surface Soil ◽  
Root Zone ◽  
Surface Soil Moisture ◽  
Near Surface ◽  
Model Soil ◽  
Dry Bias

Abstract. This study examines whether the assimilation of remotely sensed near-surface soil moisture observations might benefit an operational hydrological model, specifically Météo-France's SAFRAN-ISBA-MODCOU (SIM) model. Soil moisture data derived from ASCAT backscatter observations are assimilated into SIM using a Simplified Extended Kalman Filter (SEKF) over 3.5 years. The benefit of the assimilation is tested by comparison to a delayed cut-off version of SIM, in which the land surface is forced with more accurate atmospheric analyses, due to the availability of additional atmospheric observations after the near-real time data cut-off. However, comparing the near-real time and delayed cut-off SIM models revealed that the main difference between them is a dry bias in the near-real time precipitation forcing, which resulted in a dry bias in the root-zone soil moisture and associated surface moisture flux forecasts. While assimilating the ASCAT data did reduce the root-zone soil moisture dry bias (by nearly 50%), this was more likely due to a bias within the SEKF, than due to the assimilation having accurately responded to the precipitation errors. Several improvements to the assimilation are identified to address this, and a bias-aware strategy is suggested for explicitly correcting the model bias. However, in this experiment the moisture added by the SEKF was quickly lost from the model surface due to the enhanced surface fluxes (particularly drainage) induced by the wetter soil moisture states. Consequently, by the end of each winter, during which frozen conditions prevent the ASCAT data from being assimilated, the model land surface had returned to its original (dry-biased) climate. This highlights that it would be more effective to address the precipitation bias directly, than to correct it by constraining the model soil moisture through data assimilation.

scholarly journals Satellite Determination of Peatland Water Table Temporal Dynamics by Localizing Representative Pixels of A SWIR-Based Moisture Index

2020 ◽  
Vol 12 (18) ◽  
pp. 2936
Author(s):  
Iuliia Burdun ◽  
Michel Bechtold ◽  
Valentina Sagris ◽  
Annalea Lohila ◽  
Elyn Humphreys ◽  
...  
Keyword(s):  
Time Series ◽  
Soil Moisture ◽  
Water Table ◽  
Land Surface ◽  
Temporal Dynamics ◽  
Root Zone ◽  
Pearson Correlation ◽  
Remotely Sensed ◽  
Rooting Depth ◽  
Surface Model

The OPtical TRApezoid Model (OPTRAM) is a physically-based approach for remote soil moisture estimation. OPTRAM is based on the response of short-wave infrared (SWIR) reflectance to vegetation water status, which in turn responds to changes of root-zone soil moisture. In peatlands, the latter is tightly coupled to water table depth (WTD). Therefore, in theory, the OPTRAM index might be a useful tool to monitor WTD dynamics in peatlands, although the sensitivity of OPTRAM index to WTD changes will likely depend on vegetation cover and related rooting depth. In this study, we aim at identifying those locations (further called ‘best pixels’) where the OPTRAM index is most representative of overall peatland WTD dynamics. In peatlands, the high saturated hydraulic conductivity of the upper layer largely synchronizes the temporal WTD fluctuations over several kilometers, i.e., even though the mean and amplitude of the WTD dynamics may vary in space. Therefore, it can be assumed that the WTD time series, either measured at a single location or simulated for a grid cell with the PEATland-specific adaptation of the NASA Catchment Land Surface Model (PEATCLSM), are representative of the overall peatland WTD dynamics. We took advantage of this concept to identify the ‘best pixel’ of all spatially distributed OPTRAM pixels within a peatland, as that pixel with the highest time series Pearson correlation (R) with WTD data accounting for temporal autocorrelation. The OPTRAM index was calculated based on various remotely sensed images, namely, Landsat, MODIS, and aggregated Landsat images at MODIS resolution for five northern peatlands with long-term WTD records, including both bogs and fens. The ‘best pixels’ were dominantly covered with mosses and graminoids with little or no shrub or trees. However, the performance of OPTRAM highly depended on the spatial resolution of the remotely sensed data. The Landsat-based OPTRAM index yielded the highest R values (mean of 0.7 across the ‘best pixels’ in five peatlands). Our study further indicates that, in the absence of historical in situ data, PEATCLSM can be used as an alternative to localize ‘best pixels’. This finding enables the future applicability of OPTRAM to monitor WTD changes in peatlands on a global scale.

The Soil System

2003 ◽  
Author(s):  
Arthur W. Warrick
Keyword(s):  
Water Table ◽  
Vadose Zone ◽  
Soil Profile ◽  
Atmospheric Pressure ◽  
Root Zone ◽  
Pore Space ◽  
Critical Role ◽  
Chemical Properties ◽  
Parent Material ◽  
Capillary Fringe

Soil exists at the boundary between the atmosphere and the Earth’s subsurface. It plays a critical role in the hydrologic cycle, in addition to serving as the location of most human activity. An examination below the Earth’s surface generally reveals a profile similar to that shown in figure 1-1 A. The first zone encountered is the soil zone. This soil has developed from parent material through biological and other factors of weathering. If time is sufficient, then horizons will have formed with differing physical and chemical properties. At greater depths the soil merges with additional unconsolidated material. Eventually, at still greater depths, bedrock is encountered. The dimensions of these various zones are highly variable. For example, the soil profile may exist on bedrock that is partially exposed at the soil surface. Conversely, the unconsolidated layer can be hundreds of meters thick, as is the case in many alluvial basins. The subsurface can also be described in terms of water regimes that exist.The hydrologic profile consists of the vadose zone and the phreatic zone. The vadose zone is from the ground surface to the permanent water table, and includes the root zone, the soil profile, and the capillary fringe, which is a tension-saturated zone bordering the water table. The water at the water table is at atmospheric pressure; above the water table the pressure is less than atmospheric pressure and below the water table it is greater. The system is unsaturated above the capillary fringe, meaning that not only is the water under tension, but that some of the pore space is filled with air. The extent of the capillary fringe is dependent on the porous material. Generally, itextends a few centimeters for coarse material, or perhaps a meter for fine materials. A more complete depiction would include further saturated regions in the vadose zone, such as those due to surface infiltration or due to impeding layers that result in a perched water. Historically, the term groundwater was used to denote water beneath the permanent water table, but it is now commonly used to describe all subsurface water.

scholarly journals Influence of the vadose zone on groundwater pollution - A review

2019 ◽  
Vol 1 (1) ◽  
pp. 41-44
Author(s):  
Banajarani Panda ◽  
Chidambaram S
Keyword(s):  
Soil Properties ◽  
Water Content ◽  
Water Table ◽  
Vadose Zone ◽  
Groundwater Pollution ◽  
Land Surface ◽  
Unsaturated Zone ◽  
Water Movement ◽  
Ground Surface ◽  
Fluid Distribution

The vadose zone is the geologic profile that lies between the water table and the ground surface. It has low water content relative to the saturated zone and commonly referred as the unsaturated zone. Recharge to the water table passes through the vadose zone and understanding transport through this region is critical in groundwater pollution studies. Groundwater pollution is controlled by a number of physical and chemical processes which may retard or transform contaminants as they pass through the vadose zone.  Porous materials hold water under tension as a component of soil structure, ambient fluid pressures and other factors. When vadose zone water content is below saturation, leakage liquid as well as the dissolved materials passed on in it are retained. Hydrologically, the depth of unsaturated zone plays an important role in controlling water movement and contaminant transport from the land surface to the aquifer. The purpose of this study is to present an overview of the principles of fluid flow and moisture retention in the vadose zone and its influence on groundwater pollution. The study is presented in two parts: Part I includes descriptions of zones of soil moisture, basic principles of properties controlling the fluid distribution in pore spaces and how subsurface soil properties can be used to assess the leachate mobility. Part II review the principle of fluid movement in the vadose zone and impact of seepage on groundwater pollution. This study will focus on how vadose zone conditions and soil properties act to control groundwater pollution.

scholarly journals Assimilation of ASCAT near-surface soil moisture into the French SIM hydrological model

2011 ◽  
Vol 8 (3) ◽  
pp. 5427-5464 ◽  
Author(s):  
C. Draper ◽  
J.-F. Mahfouf ◽  
J.-C. Calvet ◽  
E. Martin ◽  
W. Wagner
Keyword(s):  
Soil Moisture ◽  
Real Time ◽  
Land Surface ◽  
Hydrological Model ◽  
Surface Soil ◽  
Root Zone ◽  
Degree Of Saturation ◽  
Surface Soil Moisture ◽  
Near Surface ◽  
The Mean

Abstract. The impact of assimilating near-surface soil moisture into the SAFRAN-ISBA-MODCOU (SIM) hydrological model over France is examined. Specifically, the root-zone soil moisture in the ISBA land surface model is constrained over three and a half years, by assimilating the ASCAT-derived surface degree of saturation product, using a Simplified Extended Kalman Filter. In this experiment ISBA is forced with the near-real time SAFRAN analysis, which analyses the variables required to force ISBA from relevant observations available before the real time data cut-off. The assimilation results are tested against ISBA forecasts generated with a higher quality delayed cut-off SAFRAN analysis. Ideally, assimilating the ASCAT data will constrain the ISBA surface state to correct for errors in the near-real time SAFRAN forcing, the most significant of which was a substantial dry bias caused by a dry precipitation bias. The assimilation successfully reduced the mean root-zone soil moisture bias, relative to the delayed cut-off forecasts, by close to 50 % of the open-loop value. The improved soil moisture in the model then led to significant improvements in the forecast hydrological cycle, reducing the drainage, runoff, and evapotranspiration biases (by 17 %, 11 %, and 70 %, respectively). When coupled to the MODCOU hydrogeological model, the ASCAT assimilation also led to improved streamflow forecasts, increasing the mean discharge ratio, relative to the delayed cut off forecasts, from 0.68 to 0.76. These results demonstrate that assimilating near-surface soil moisture observations can effectively constrain the SIM model hydrology, while also confirming the accuracy of the ASCAT surface degree of saturation product. This latter point highlights how assimilation experiments can contribute towards the difficult issue of validating remotely sensed land surface observations over large spatial scales.

Combining subsurface drainage and windbreaks to control dryland salinity

2006 ◽  
Vol 86 (3) ◽  
pp. 555-563
Author(s):  
H. Steppuhn
Keyword(s):  
Vadose Zone ◽  
Land Surface ◽  
Root Zone ◽  
Subsurface Drainage ◽  
Water Levels ◽  
Blowing Snow ◽  
Dryland Salinity ◽  
Water Tables ◽  
The Mean ◽  
A Site

The reclamation of salinized soil involves lowering ground water levels, draining the vadose zone, and leaching the salts from the root zone. Plastic drain tubing placed 1.5 to 1.8 m below the land surface can lower water tables and drain phreatic water, but irrigation is usually required to leach the offending salts. The leaching process in non-irrigated drylands depends on natural precipitation. Rows of tall wheatgrass, Thinopyrum ponticum (Podp.) Lui & Wang, (1.2 m mean height) spaced on 15.2-m centres across saline fields can retain blowing snow, augment water for leaching salts, and moderate evapotranspiration, especially when grown in conjunction with subsurface drainage. The mean salinity of saturated soil paste extracts from sets of soil samples taken every fall from such a site in southwestern Saskatchewan averaged 14.1 dS m-1 during 1985–1990 before the drainage was installed, 13.0 dS m-1 for 1991–1992 after drainage but before the grass windbreaks became established, and 9.6 dS m-1 for 1993–1998 with both drainage and windbreaks in place. Key words: Saline soil, engineered drainage, snow management, grass barriers

A New Automated Passive Capillary Lysimeter for Logging Real-Time Drainage Water Fluxes

2017 ◽  
Vol 33 (6) ◽  
pp. 849-857
Author(s):  
J. D. Jabro ◽  
W. M. Iversen ◽  
W. B. Stevens ◽  
B. L. Allen ◽  
U. M. Sainju
Keyword(s):  
Real Time ◽  
Vadose Zone ◽  
Spread Spectrum ◽  
Root Zone ◽  
Sandy Loam ◽  
Irrigation System ◽  
Cropping Systems ◽  
Soil Surface ◽  
Drainage Water ◽  
Water Fluxes

Abstract.Effective monitoring of chemical transport through the soil profile requires accurate and appropriate instrumentation to measure drainage water fluxes below the root zone of cropping systems. The objectives of this study were to methodically describe in detail the construction and installation of a novel automated PCAP (passive capillary) lysimeter design, and to evaluate the efficacy of this design for logging and monitoring real-time drainage water fluxes occurring below the root zone of corn ( L.) and soybean ( L.) under an overhead sprinkler irrigation system. Sixteen cylindrical PCAP lysimeters with outside dimensions of 32.39 cm in diameter ×74.8 cm height (1000 cm2 surface area) were designed, constructed, and placed 90 cm below the soil surface in a Lihen sandy loam. Two watermark soil moisture and temperature sensors were positioned at 30 and 76 cm depths above each PCAP to monitor soil temperature and water potential continuously. This new design incorporated wireless spread spectrum technology to enable an automated datalogger to transmit drainage water amounts simultaneously every 15 min to a remote host. Logged drainage amounts were compared with those manually collected using several statistical methods. The root mean square error (RMSE), the logging efficacy (EF), and the mean difference (MD) were 0.0375, 0.964 and 0.0335 cm, respectively, for 4-yr combined data. The MD between logged and collected drainage amounts was very small and not significantly different from zero for 4-yr combined results. Statistical results indicated that the new lysimeter performed exceptionally well and was capable of monitoring drainage water fluxes in the vadose zone. Real-time seamless monitoring and logging drainage water fluxes was thus possible without the need for costly time-consuming supportive procedures. Keywords: Drainage, Lysimeter, Root zone, Vadose zone.

Conception of vadose zone research in the area of Goczałkowice reservoir.

2013 ◽  
Vol 2 (1) ◽  
pp. 22-26
Author(s):  
Joanna Czekaj ◽  
Kamil Trepka
Keyword(s):  
Vadose Zone ◽  
Unsaturated Zone ◽  
Vertical Profile ◽  
Structural Model ◽  
Historical Data ◽  
Integrated System ◽  
Nitrate Transport ◽  
Strategic Research ◽  
Research Site ◽  
Observation Wells

Abstract Goczałkowice reservoir is one of the main source of drinking water for Upper Silesia Region. In reference to Water Frame Directive matter since 2010 the strategic research project: „Integrated system supporting management and protection of dammed reservoir (ZiZoZap)”, which is being conducted on Goczałkowice reservoir, has been pursued. In the framework of this project complex groundwater monitoring is carried on. One aspect is vadose zone research, conducted to obtain information about changes in chemical composition of infiltrating water and mass transport within this zone. Based on historical data and the structural model of direct catchment of Goczałkowice reservoir location of the vadose zone research site was selected. At the end of November 2012 specially designed lysimeter was installed with 10 MacroRhizon samplers at each lithological variation in unsaturated zone. This lysimeter, together with nested observation wells, located in the direct proximity, create the vadose zone research site which main aim is specifying the amount of nitrate transport in the vertical profile.

Impact of LULC Changes on LST in Rajshahi District of Bangladesh: A Remote Sensing Approach

2020 ◽  
Vol 3 (1) ◽  
pp. 11-23 ◽  
Author(s):  
Abdulla Al Kafy ◽  
Abdullah Al-Faisal ◽  
Mohammad Mahmudul Hasan ◽  
Md. Soumik Sikdar ◽  
Mohammad Hasib Hasan Khan ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Surface Temperature ◽  
Land Surface ◽  
Agricultural Land ◽  
Global Climate ◽  
Urban Expansion ◽  
Water Bodies ◽  
Landsat 8 ◽  
Lulc Changes ◽  
The Impact

Urbanization has been contributing more in global climate warming, with more than 50% of the population living in cities. Rapid population growth and change in land use / land cover (LULC) are closely linked. The transformation of LULC due to rapid urban expansion significantly affects the functions of biodiversity and ecosystems, as well as local and regional climates. Improper planning and uncontrolled management of LULC changes profoundly contribute to the rise of urban land surface temperature (LST). This study evaluates the impact of LULC changes on LST for 1997, 2007 and 2017 in the Rajshahi district (Bangladesh) using multi-temporal and multi-spectral Landsat 8 OLI and Landsat 5 TM satellite data sets. The analysis of LULC changes exposed a remarkable increase in the built-up areas and a significant decrease in the vegetation and agricultural land. The built-up area was increased almost double in last 20 years in the study area. The distribution of changes in LST shows that built-up areas recorded the highest temperature followed by bare land, vegetation and agricultural land and water bodies. The LULC-LST profiles also revealed the highest temperature in built-up areas and the lowest temperature in water bodies. In the last 20 years, LST was increased about 13ºC. The study demonstrates decrease in vegetation cover and increase in non-evaporating surfaces with significantly increases the surface temperature in the study area. Remote-sensing techniques were found one of the suitable techniques for rapid analysis of urban expansions and to identify the impact of urbanization on LST.

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