High-Frequency Stable-Isotope Measurements of Evapotranspiration Partitioning in a Maize Field

Knowledge of the evaporation (E) and transpiration (T) components of evapotranspiration (ET) is important for ecohydrological modeling and agricultural productivity. The stable-isotope method offers the possibility to partition E and T due to the distinct differences in the isotopic signals of the sources. In this study, the concentration and isotopic ratios for oxygen-18 (18O) of water vapor in the ecosystem boundary layer of a growing maize field at the Hydrological Open Air Laboratory (HOAL) catchment in Austria were measured using a high-frequency field-sampling device. In conjunction with isotope samples from the soil and maize plants, these data were used to partition ET using the Keeling plot technique. Eddy covariance and sap flow measurements were used to provide a comparison to test the stable-isotope method. The fraction of transpiration (Ft) calculated with the stable-isotope method showed good agreement with the sap flow method. Overall daily average values of Ft were in a range from 43.0 to 88.5% with T accounting for an average value of 67.5% of the evapotranspiration over the nine days of the experimental period. Following a precipitation event of 9.7 mm, Ft increased from 63.4 to 88.5% over the next four days as the upper layer of the soil dried out while the plants accessed deeper soil water.

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CO<sub>2</sub> uptake of a mature <i>Acacia mangium</i> plantation estimated from sap flow measurements and stable carbon isotope discrimination

Biogeosciences Discussions ◽

10.5194/bgd-10-11583-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 11583-11625 ◽

Cited By ~ 3

Author(s):

H. Wang ◽

P. Zhao ◽

L. L. Zou ◽

H. R. McCarthy ◽

X. P. Zeng ◽

...

Keyword(s):

Stomatal Conductance ◽

Stable Isotope ◽

Carbon Isotope ◽

Sap Flow ◽

Carbon Isotope Discrimination ◽

Stable Carbon Isotope ◽

Sap Flux ◽

Stable Carbon ◽

Flow Measurements ◽

Sap Flow Measurements

Abstract. Canopy CO2 uptake (FCO2) of a subtropical mature \\textit{A. mangium} plantation was estimated by combining sap flow measurements and stable carbon isotope discrimination (Δ) in Southern China from 2004 to 2007. The mechanistic relationship linking FCO2, Δ in leaf sap, and sap flow based canopy stomatal conductance (Gs) was applied in our study. No significant seasonal variations were observed in Δ or in the ratio of the intercellular and ambient CO2 concentrations (Ci/Ca), although diurnal Ci/Ca varied between sunlit and shaded leaves. A sensitivity analysis showed that estimates of FCO2 were more sensitive to dynamics in Gs than in Ca and Δ. By using seasonally and canopy averaged Ci/Ca values, an acceptable estimate of FCO2 was obtained. FCO2 exhibited similar diurnal variation to that of Gs. Large seasonal variation in FCO2 was attributed to the responsiveness of Gs to vapour pressure deficit, photosynthetically active radiation, and soil moisture deficit. Our estimate of FCO2 for a mature A. mangium plantation (2.13 ± 0.40 g C m−2 day−1) approached the lower range of values for subtropical mixed forest, probably due to lower mean canopy stomatal conductance, higher Ci/Ca, and greater tree height than other measured forests. Our estimate was also lower than values determined by satellite-based modeling or component carbon analysis, suggesting the necessity of stand level flux data for verification. Qualitatively, the sap flux/stable isotope results compared well with gas exchange results. Differences in results between the two approaches reflected variability due to leaf position and age, which could be reduced for sap flux/stable isotope, which uses canopy average values of Gs and Ci/Ca.

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A new method of fluxgate signal extraction

Information extraction and processing ◽

10.15407/vidbir2017.45.083 ◽

2017 ◽

Vol 2017 (45) ◽

pp. 83-89

Author(s):

A.A. Marusenkov ◽

Keyword(s):

High Frequency ◽

Second Harmonic ◽

Excitation Frequency ◽

Low Noise ◽

Measuring System ◽

Signal Extraction ◽

Fluxgate Magnetometer ◽

New Approach ◽

Average Value ◽

The Time Domain

Using dedicated high-frequency measuring system the distribution of the Barkhausen jumps intensity along a reversal magnetization cycle was investigated for low noise fluxgate sensors of various core shapes. It is shown that Barkhausen (reversal magnetization) noise intensity is strongly inhomogeneous during an excitation cycle. In the traditional second harmonic fluxgate magnetometers the signals are extracted in the frequency domain, as a result, some average value of reversal magnetization noises is contributed to the output signals. In order to fit better the noise shape and minimize its transfer to the magnetometer output the new approach for demodulating signals of these sensors is proposed. The new demodulating method is based on information extraction in the time domain taking into account the statistical properties of cyclic reversal magnetization noises. This approach yields considerable reduction of the fluxgate magnetometer noise in comparison with demodulation of the signal filtered at the second harmonic of the excitation frequency.

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