scholarly journals Long-term and high frequency non-destructive monitoring of water stable isotope profiles in an evaporating soil column

2015 ◽  
Vol 12 (4) ◽  
pp. 3893-3918 ◽  
Author(s):  
Y. Rothfuss ◽  
S. Merz ◽  
J. Vanderborght ◽  
N. Hermes ◽  
A. Weuthen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Stable Isotope ◽  
Soil Water ◽  
Temporal Resolution ◽  
Liquid Water ◽  
Classical Method ◽  
Soil Column ◽  
Soil Surface ◽  
High Temporal Resolution ◽  
Non Destructive

Abstract. The stable isotope compositions of soil water (δ2H and δ18O) carry important information about the prevailing soil hydrological conditions and for constraining ecosystem water budgets. However, they are highly dynamic, especially during and after precipitation events. The classical method of determining soil water δ2H and δ18O at different depths, i.e., soil sampling and cryogenic extraction of the soil water, followed by isotope-ratio mass spectrometer analysis is destructive and laborious with limited temporal resolution. In this study, we present a new non-destructive method based on gas-permeable tubing and isotope-specific infrared laser absorption spectroscopy. We conducted a laboratory experiment with an acrylic glass column filled with medium sand equipped with gas-permeable tubing at eight different soil depths. The soil column was initially saturated from the bottom, exposed to evaporation for a period of 290 days, and finally rewatered. Soil water vapor δ2H and δ18O were measured daily, sequentially for each depth. Soil liquid water δ2H and δ18O were inferred from the isotopic values of the vapor assuming thermodynamic equilibrium between liquid and vapor phases in the soil. The experimental setup allowed following the evolution of typical exponential-shaped soil water δ2H and δ18O profiles with unprecedentedly high temporal resolution. As the soil dried out, we could also show for the first time the increasing influence of the isotopically depleted ambient water vapor on the isotopically enriched liquid water close to the soil surface (i.e., atmospheric invasion). Rewatering at the end of the experiment led to instantaneous resetting of the stable isotope profiles, which could be closely followed with the new method.

scholarly journals Long-term and high-frequency non-destructive monitoring of water stable isotope profiles in an evaporating soil column

2015 ◽  
Vol 19 (10) ◽  
pp. 4067-4080 ◽  
Author(s):  
Y. Rothfuss ◽  
S. Merz ◽  
J. Vanderborght ◽  
N. Hermes ◽  
A. Weuthen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Stable Isotope ◽  
Soil Water ◽  
Liquid Water ◽  
Isotope Effects ◽  
Soil Column ◽  
Soil Surface ◽  
Kinetic Isotope Effects ◽  
Experimental Conditions ◽  
Kinetic Isotope

Abstract. The stable isotope compositions of soil water (δ2H and δ18O) carry important information about the prevailing soil hydrological conditions and for constraining ecosystem water budgets. However, they are highly dynamic, especially during and after precipitation events. In this study, we present an application of a method based on gas-permeable tubing and isotope-specific infrared laser absorption spectroscopy for in situ determination of soil water δ2H and δ18O. We conducted a laboratory experiment where a sand column was initially saturated, exposed to evaporation for a period of 290 days, and finally rewatered. Soil water vapor δ2H and δ18O were measured daily at each of eight available depths. Soil liquid water δ2H and δ18O were inferred from those of the vapor considering thermodynamic equilibrium between liquid and vapor phases in the soil. The experimental setup allowed for following the evolution of soil water δ2H and δ18O profiles with a daily temporal resolution. As the soil dried, we could also show for the first time the increasing influence of the isotopically depleted ambient water vapor on the isotopically enriched liquid water close to the soil surface (i.e., atmospheric invasion). Rewatering at the end of the experiment led to instantaneous resetting of the stable isotope profiles, which could be closely followed with the new method. From simple soil δ2H and δ18O gradients calculations, we showed that the gathered data allowed one to determinate the depth of the evaporation front (EF) and how it receded into the soil over time. It was inferred that after 290 days under the prevailing experimental conditions, the EF had moved down to an approximate depth of −0.06 m. Finally, data were used to calculate the slopes of the evaporation lines and test the formulation for kinetic isotope effects. A very good agreement was found between measured and simulated values (Nash and Sutcliffe efficiency, NSE = 0.92) during the first half of the experiment, i.e., until the EF reached a depth of −0.04 m. From this point, calculated kinetic effects associated with the transport of isotopologues in the soil surface air layer above the EF provided slopes lower than observed. Finally, values of kinetic isotope effects that provided the best model-to-data fit (NSE > 0.9) were obtained from inverse modeling, highlighting uncertainties associated with the determinations of isotope kinetic fractionation and soil relative humidity at the EF.

scholarly journals Comparison between two lidar methods to retrieve microphysical properties of liquid-water clouds

2018 ◽  
Vol 176 ◽  
pp. 01032 ◽  
Author(s):  
Cristofer Jimenez ◽  
Albert Ansmann ◽  
David Donovan ◽  
Ronny Engelmann ◽  
Jörg Schmidt ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Liquid Water ◽  
High Temporal Resolution ◽  
Lidar System ◽  
Microphysical Properties

Since 2010, the Raman dual-FOV lidar system permits the retrieval of microphysical properties of liquid-water clouds during nighttime. A new robust lidar depolarization approach was recently introduced, which permits the retrieval of these properties as well, with high temporal resolution and during daytime. To implement this approach, the lidar system was upgraded, by adding a three channel depolarization receiver. The first preliminary retrieval results and a comparison between both methods is presented.

scholarly journals Characterization of high temporal resolution prr acquisition by fast comtec card: Deadtime, PRR desaturation, temperature calibration and retrieval.

2018 ◽  
Vol 176 ◽  
pp. 01017 ◽  
Author(s):  
Giovanni Martucci ◽  
Valentin Simeonov ◽  
Ludovic Renaud ◽  
Alexander Haefele
Keyword(s):  
Water Vapor ◽  
Temporal Resolution ◽  
Dead Time ◽  
Temporal Stability ◽  
Acquisition System ◽  
High Temporal Resolution ◽  
Temperature Calibration ◽  
Raman Lidar ◽  
Meteorological Observations

RAman Lidar for Meteorological Observations (RALMO) is operated at MeteoSwiss and provides continuous measurements of water vapor and temperature since 2010. While the water vapor has been acquired by a Licel acquisition system since 2008, the temperature channels have been migrated to a Fastcom P7888 acquisition system, since August 2015. We present a characterization of this new acquisition system, namely its dead-time, desaturation, temporal stability of the Pure Rotational Raman signals and the retrieval of the PRR-temperature.

scholarly journals Measuring Soil Water Content under Turfgrass Using the Dual-probe Heat-pulse Technique

1998 ◽  
Vol 123 (5) ◽  
pp. 937-941 ◽  
Author(s):  
Y. Song ◽  
J.M. Ham ◽  
M.B. Kirkham ◽  
G.J. Kluitenberg
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Tall Fescue ◽  
Soil Column ◽  
Gravimetric Method ◽  
Soil Surface ◽  
Heat Pulse ◽  
Pulse Technique ◽  
Dual Probe

Measurements of soil water content near the soil surface often are required for efficient turfgrass water management. Experiments were conducted in a greenhouse to determine if the dual-probe heat-pulse (DPHP) technique can be used to monitor changes in soil volumetric water content (θv) and turfgrass water use. `Kentucky 31' Tall fescue (Festuca arundinacea Schreb.) was planted in 20-cm-diameter containers packed with Haynie sandy loam (coarse-silty, mixed, calcareous, mesic Typic Udifluvents). Water content was measured with the DPHP sensors that were placed horizontally at different depths between 1.5 and 14.4 cm from the surface in the soil column. Water content also was monitored gravimetrically from changes in container mass. Measurements started when the soil surface was covered completely by tall fescue. Hence, changes in θv could be attributed entirely to water being taken up by roots of tall fescue. Daily measurements were taken over multiple 6- or 7-day drying cycles. Each drying cycle was preceded by an irrigation, and free drainage had ceased before measurements were initiated. Soil water content dropped from ≈0.35 to 0.10 m3·m-3 during each drying cycle. Correlation was excellent between θv and changes in water content determined by the DPHP and gravimetric methods. Comparisons with the gravimetric method showed that the DPHP sensors could measure average container θv within 0.03 m3·m-3 and changes in soil water content within 0.01 m3·m-3.

scholarly journals A global database of water vapor isotopes measured with high temporal resolution infrared laser spectroscopy

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Zhongwang Wei ◽  
Xuhui Lee ◽  
Franziska Aemisegger ◽  
Marion Benetti ◽  
Max Berkelhammer ◽  
...  
Keyword(s):  
Water Vapor ◽  
Laser Spectroscopy ◽  
Temporal Resolution ◽  
Infrared Laser ◽  
High Temporal Resolution ◽  
Global Database ◽  
Infrared Laser Spectroscopy

scholarly journals Synergy of Satellite- and Ground-Based Observations for Continuous Monitoring of Atmospheric Stability, Liquid Water Path, and Integrated Water Vapor: Theoretical Evaluations Using Reanalysis and Neural Networks

2020 ◽  
Vol 59 (7) ◽  
pp. 1153-1170
Author(s):  
Maria Toporov ◽  
Ulrich Löhnert
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Temporal Resolution ◽  
Liquid Water ◽  
Atmospheric Stability ◽  
Satellite Observations ◽  
Liquid Water Path ◽  
Water Path ◽  
Atmospheric State ◽  
Humidity Profiles

AbstractAtmospheric stability plays an essential role in the evolution of weather events. While the upper troposphere is sampled by satellite sensors, and in situ sensors measure the atmospheric state close to the surface, only sporadic information from radiosondes or aircraft observations is available in the planetary boundary layer. Ground-based remote sensing offers the possibility to continuously and automatically monitor the atmospheric state in the boundary layer. Microwave radiometers (MWR) provide temporally resolved temperature and humidity profiles in the boundary layer and accurate values of integrated water vapor and liquid water path, and the differential absorption lidar (DIAL) measures humidity profiles with high vertical and temporal resolution up to 3000-m height. Both instruments have the potential to complement satellite observations by additional information from the lowest atmospheric layers, particularly under cloudy conditions. This study presents a neural network retrieval for stability indices, integrated water vapor, and liquid water path from simulated satellite- and ground-based measurements based on the COSMO regional reanalysis (COSMO-REA2). Focusing on the temporal resolution, the satellite-based instruments considered in the study are the currently operational Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the future Infrared Sounder (IRS), both in geostationary orbit. Relative to the retrieval based on satellite observations, the additional ground-based MWR/DIAL measurements provide valuable improvements not only in the presence of clouds, which represent a limiting factor for infrared SEVIRI/IRS, but also under clear-sky conditions. The root-mean-square error for convective available potential energy, for instance, is reduced by 24% if IRS observations are complemented by ground-based MWR measurements.

scholarly journals Continuous, near-real-time observations of water stable isotope ratios during rainfall and throughfall events

2019 ◽  
Vol 23 (7) ◽  
pp. 3007-3019 ◽  
Author(s):  
Barbara Herbstritt ◽  
Benjamin Gralher ◽  
Markus Weiler
Keyword(s):  
Stable Isotope ◽  
Isotopic Composition ◽  
Real Time ◽  
Temporal Resolution ◽  
Tree Canopy ◽  
Dead Volume ◽  
High Temporal Resolution ◽  
Time Lags ◽  
Mixing Processes ◽  
Water Stable Isotope

Abstract. The water isotopic composition of throughfall is affected by complex diffusive exchange with ambient water vapour, evaporative enrichment of heavy isotopes, and mixing processes in the tree canopy. All interception processes occur simultaneously in space and time, generating a complex pattern of throughfall depth and water isotopic composition. This pattern ultimately cascades through the entire hydrologic system and is therefore crucial for isotope studies in catchment hydrology, where recharge areas are often forested, while reference meteorological stations are generally in the open. For the quasi real-time observation of the water isotopic composition (δ18O and δ2H) of both gross precipitation and throughfall, we developed an approach combining a membrane contactor (Membrana) with a laser-based Cavity Ring-Down Spectrometer (CRDS, Picarro), obtaining isotope readings every 2 s. A setup with two CRDS instruments in parallel analysing gross precipitation and throughfall simultaneously was used for the continuous observation of the temporal effect of interception processes on the stable isotopes of water. All devices were kept small to minimize dead volume with time lags of only 4 min for water from the rainfall collectors to the isotope analysers to increase the temporal resolution of isotope observations. Complementarily, meteorological variables were recorded at high temporal resolution at the same location. The achieved evolution from discrete liquid or event-based bulk samples to continuous measurements allows for direct comparison of water stable isotope data with common meteorological measurements. Future improvements of the spatial representativeness will make our approach an even more powerful tool towards detailed insight into the dynamic processes contributing to interception during rainfall events.

Isotope labeling experiment to infer ecohydrological travel times

2020 ◽  
Author(s):  
David Mennekes ◽  
Michael Rinderer ◽  
Stefan Seeger ◽  
Hugo de Boer ◽  
Natalie Orlowski ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Uptake ◽  
Temporal Resolution ◽  
Water Vapor Pressure ◽  
Root Water Uptake ◽  
Field Conditions ◽  
High Temporal Resolution ◽  
Travel Times ◽  
Isotope Measurements

<p>Stable water isotopes are promising tracers to study soil-tree interactions and root water uptake. Traditionally, destructive sampling techniques are applied to measure the isotopic signature in soils and plant tissues but these methods are limited in their temporal resolution. For calculating ecohydrological travel times from soil water to transpiration, high frequent isotope measurements are required. Recently, in-situ water isotope probes have been successfully applied in beech trees to yield high-frequent isotope measurements under field conditions but the complexity and heterogeneity of natural field conditions can make a systematical method testing difficult. Here, we test whether the new probes are capable of capturing tree species-specific differences in root water uptake and associated travel times.<br>We test this in a controlled experiment using large pots with three 4-6 meter high and 20 year old coniferous and deciduous trees: <em>Pinus pinea</em>, <em>Alnus</em> <em>x spaethii</em> and <em>Quercus</em> <em>suber</em> that are expected to have different water uptake strategies. We applied deuterated irrigation water to the homogeneous soils in the pots and traced the water flux from the soils through the trees with in-situ isotope probes in high temporal resolution.<br>This contribution presents preliminary results on ecohydrological travel times in relation to environmental parameters such as sap flow, photosynthetic activity, matrix potential, soil water content, water vapor pressure deficit and solar radiation.<br>Our in-situ isotope probes were capable to capture the breakthrough of the isotope tracer in all trees. The calculated travel times were shorter for the Pinus and Alnus compared to the Quercus which suggests differences in root water uptake. Detailed results from such controlled experiments are fundamental for testing new measurement techniques such as the in-situ isotope probes. Such results are important to better interpret results measured under natural and therefore more complex and heterogeneous field conditions.</p>

scholarly journals Water Vapor Exchange between Soil and Atmosphere over a Gobi Surface near an Oasis in the Summer

2004 ◽  
Vol 43 (12) ◽  
pp. 1917-1928 ◽  
Author(s):  
Qiang Zhang ◽  
Ronghui Huang
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Soil Layer ◽  
Soil Surface ◽  
Northwest China ◽  
Atmospheric Humidity ◽  
Shallow Layer ◽  
Using Data

Abstract Using data observed at Dunhuang, in the Gansu, in the arid region of northwest China in the summer, the characteristics of the soil water content, temperature, and atmospheric humidity were analyzed. It was found that the depth of the active soil temperature layer is about 5 cm, which is much thinner than that of typical soils. In addition, not only is the atmospheric humidity gradient in the surface layer often inverted, but so too is the soil water content gradient in the shallow layer. The diurnal variation of soil water content can be divided into four stages, including wet, water loss, dry, and water gain. It is shown that in soil water content profiles the depth of the active soil layer is about 10 cm, and soil water content inversion is the primary feature in the shallow layer during the “wet” stage. The presence of soil water content inversion indicates that soil in the shallow layer can absorb water from the air through condensation in the nighttime and emit water vapor to the air through evaporation in the daytime. The formation of a soil water content inversion is mainly related to the state of the soil surface temperature.

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