scholarly journals First on-line isotopic characterization of N<sub>2</sub>O above intensively managed grassland

2015 ◽  
Vol 12 (8) ◽  
pp. 2517-2531 ◽  
Author(s):  
B. Wolf ◽  
L. Merbold ◽  
C. Decock ◽  
B. Tuzson ◽  
E. Harris ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Temporal Resolution ◽  
Isotopic Signature ◽  
Repeated Measurements ◽  
Spectrometric Analysis ◽  
High Temporal Resolution ◽  
Site Preference ◽  
Nitrifier Denitrification ◽  
Isotopic Characterization ◽  
Intensively Managed

Abstract. The analysis of the four main isotopic N2O species (14N14N16O, 14N15N16O, 15N14N16O, 14N14N18O) and especially the intramolecular distribution of 15N ("site preference", SP) has been suggested as a tool to distinguish source processes and to help constrain the global N2O budget. However, current studies suffer from limited spatial and temporal resolution capabilities due to the combination of discrete flask sampling with subsequent laboratory-based mass-spectrometric analysis. Quantum cascade laser absorption spectroscopy (QCLAS) allows the selective high-precision analysis of N2O isotopic species at trace levels and is suitable for in situ measurements. Here, we present results from the first field campaign, conducted on an intensively managed grassland site in central Switzerland. N2O mole fractions and isotopic composition were determined in the atmospheric surface layer (at 2.2 m height) at a high temporal resolution with a modified state-of-the-art laser spectrometer connected to an automated N2O preconcentration unit. The analytical performance was determined from repeated measurements of a compressed air tank and resulted in measurement repeatability of 0.20, 0.12 and 0.11‰ for δ15Nα, δ15Nβ and δ18O, respectively. Simultaneous eddy-covariance N2O flux measurements were used to determine the flux-averaged isotopic signature of soil-emitted N2O. Our measurements indicate that, in general, nitrifier-denitrification and denitrification were the prevalent sources of N2O during the campaign and that variations in isotopic composition were due to alterations in the extent to which N2O was reduced to N2 rather than to other pathways, such as hydroxylamine oxidation. Management and rewetting events were characterized by low values of the intramolecular 15N site preference (SP), δ15Nbulk and δ18O, suggesting that nitrifier-denitrification and incomplete heterotrophic bacterial denitrification responded most strongly to the induced disturbances. The flux-averaged isotopic composition of N2O from intensively managed grassland was 6.9 ± 4.3, −17.4 ± 6.2 and 27.4 ± 3.6‰ for SP, δ15Nbulk and δ18O, respectively. The approach presented here is capable of providing long-term data sets also for other N2O-emitting ecosystems, which can be used to further constrain global N2O inventories.

scholarly journals First on-line isotopic characterization of N<sub>2</sub>O emitted from intensively managed grassland

2015 ◽  
Vol 12 (2) ◽  
pp. 1573-1611 ◽  
Author(s):  
B. Wolf ◽  
L. Merbold ◽  
C. Decock ◽  
B. Tuzson ◽  
E. Harris ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Temporal Resolution ◽  
Isotopic Signature ◽  
Repeated Measurements ◽  
Spectrometric Analysis ◽  
High Temporal Resolution ◽  
Site Preference ◽  
Nitrifier Denitrification ◽  
Isotopic Characterization ◽  
Intensively Managed

Abstract. The analysis of the four main isotopic N2O species (14N14N16O, 14N15N16O, 15N14N16O, 14N14N18O) and especially the intramolecular distribution of 15N (site preference, SP) has been suggested as a tool to distinguish source processes and to help constrain the global N2O budget. However, current studies suffer from limited spatial and temporal resolution capabilities due to the combination of discrete flask sampling with subsequent laboratory-based mass spectrometric analysis. Quantum cascade laser absorption spectroscopy (QCLAS) allows selective high-precision analysis of N2O isotopic species at trace levels and is suitable for in situ measurements. Here, we present results from the first field campaign, conducted on an intensively managed grassland in central Switzerland. N2O mole fractions and isotopic composition were determined in the atmospheric surface layer (2 m height) at high temporal resolution with a modified state-of-the-art laser spectrometer connected to an automated N2O preconcentration unit. The analytical performance was determined from repeated measurements of a compressed air tank and resulted in measurement repeatability of 0.20, 0.12 and 0.11‰ for δ15Nα, δ15Nβ and δ18O, respectively. Simultaneous eddy-covariance N2O flux measurements were used to determine the flux-averaged isotopic signature of soil-emitted N2O. Our measurements indicate that in general, nitrifier-denitrification and denitrification were the prevalent sources of N2O during the campaign, and that variations in isotopic composition were rather due to alterations in the extent to which N2O was reduced to N2, than other pathways such as hydroxylamine oxidation. Management and rewetting events were characterized by low values of the intra-molecular 15N site preference (SP), δ15Nbulk and δ18O, suggesting nitrifier denitrification and incomplete heterotrophic bacterial denitrification responded most strongly to the induced disturbances. Flux-averaged isotopic composition of N2O from intensively managed grassland was 6.9 ± 4.3, -17.4 ± 6.2 and 27.4 ± 3.6‰ for SP, δ15Nbulk and δ18O, respectively. The approach presented here is capable of providing long-term datasets also for other N2O emitting ecosystems, which can be used to further constrain global N2O inventories.

scholarly journals Real-time observations of stable isotope dynamics during rainfall and throughfall events

2018 ◽  
Author(s):  
Barbara Herbstritt ◽  
Benjamin Gralher ◽  
Markus Weiler
Keyword(s):  
Isotopic Composition ◽  
Real Time ◽  
Temporal Resolution ◽  
Tree Canopy ◽  
Dead Volume ◽  
High Temporal Resolution ◽  
Time Lags ◽  
Mixing Processes ◽  
Hydrologic System ◽  
Time Observation

Abstract. The isotopic composition of throughfall is affected by complex exchange, enrichment, and mixing processes in the tree canopy. All interception processes occur simultaneously in space and time generating a complex pattern of throughfall in amount and isotopic composition. This pattern ultimately cascades through the entire hydrologic system and is therefore crucial for 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 isotopic composition of both gross precipitation and throughfall we developed an approach combining an off-the-shelf membrane contactor (Membrana) with a laser-based Cavity Ring-Down Spectrometer (CRDS, Picarro), obtaining isotope readings every two seconds. For the continuous observation of the temporal effect of interception processes two setups with two CRDS instruments in parallel were used analysing gross precipitation and throughfall simultaneously. All devices were kept small to minimize dead volume and thereby, with time-lags of only four minutes, to increase the temporal resolution of isotope observations. Complementarily, meteorological variables were recorded in high temporal resolution at the same location. Comparing these high temporally resolved continuous measurements with discrete liquid or event-based bulk samples, this approach proves to be a powerful tool towards more insight in the very dynamic processes contributing to interception during rainfall events.

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.

scholarly journals Phenomics data processing: Extracting temperature dose-response curves from repeated measurements

2021 ◽  
Author(s):  
Lukas Roth ◽  
Hans-Peter Piepho ◽  
Andreas Hund
Keyword(s):  
Temporal Resolution ◽  
Stem Elongation ◽  
Temperature Response ◽  
Repeated Measurements ◽  
High Temporal Resolution ◽  
Asymptotic Model ◽  
Parametric Modelling ◽  
Response Curves ◽  
Starting Point ◽  
Cardinal Temperatures

Temperature is a main driver of plant growth and development. New phenotyping tools enable quantifying the temperature response of hundreds of genotypes. Yet, particularly for field-derived data, the process of temperature response modelling bears potential flaws and pitfalls with regard to the interpretation of derived parameters. In this study, climate data from three growing seasons with differing temperature distributions served as starting point for a wheat stem elongation growth simulation, based on a four-parametric Wang-Engel temperature response function. To extract dose-responses from the simulated data, a novel approach to use temperature courses with high temporal resolution was developed. Linear and asymptotic parametric modelling approaches to predict the cardinal temperatures were investigated. An asymptotic model extracted the base and optimum temperature of growth and the maximum growth rate with high precision, whereas simpler, linear models failed to do so. However, when including seasonally changing cardinal temperatures, the prediction accuracy of the asymptotic model was strongly reduced. We conclude that using an asymptotic model based on temperature courses with high temporal resolution is suitable to extract meaningful parameters from field-based data. Consequently, applying the presented modelling approach to high-throughput phenotyping data of breeding nurseries may help selecting for climate suitability.

scholarly journals In situ observations of the isotopic composition of methane at the Cabauw tall tower site

2016 ◽  
Vol 16 (16) ◽  
pp. 10469-10487 ◽  
Author(s):  
Thomas Röckmann ◽  
Simon Eyer ◽  
Carina van der Veen ◽  
Maria E. Popa ◽  
Béla Tuzson ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
High Precision ◽  
Temporal Resolution ◽  
Isotope Ratio ◽  
Mesoscale Model ◽  
Ambient Air ◽  
High Temporal Resolution ◽  
Model Calculations ◽  
Dual Isotope

Abstract. High-precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS)-based technique for in situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands and performed in situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of (+0.25 ± 0.04) ‰ for δ13C and (−4.3 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high-precision and high-temporal-resolution dataset not only reveals the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget when they are performed at multiple sites that are representative for the entire European domain.

Multidetector-row Computed Tomography in the Assessment of Coronary Artery Disease – New Techniques and Insights

2010 ◽  
Vol 6 (2) ◽  
pp. 43 ◽  
Author(s):  
Andreas H Mahnken ◽  
Keyword(s):  
Computed Tomography ◽  
Coronary Artery Disease ◽  
Coronary Artery ◽  
Data Acquisition ◽  
Temporal Resolution ◽  
High Temporal Resolution ◽  
Multidetector Row ◽  
Ct Scanners ◽  
Artery Disease ◽  
Cardiac Mdct

Over the last decade, cardiac computed tomography (CT) technology has experienced revolutionary changes and gained broad clinical acceptance in the work-up of patients suffering from coronary artery disease (CAD). Since cardiac multidetector-row CT (MDCT) was introduced in 1998, acquisition time, number of detector rows and spatial and temporal resolution have improved tremendously. Current developments in cardiac CT are focusing on low-dose cardiac scanning at ultra-high temporal resolution. Technically, there are two major approaches to achieving these goals: rapid data acquisition using dual-source CT scanners with high temporal resolution or volumetric data acquisition with 256/320-slice CT scanners. While each approach has specific advantages and disadvantages, both technologies foster the extension of cardiac MDCT beyond morphological imaging towards the functional assessment of CAD. This article examines current trends in the development of cardiac MDCT.

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