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| Titel |
A high-resolution measurement technique for vertical CO2 and H2O profiles within and above crop canopies and its use for flux partitioning |
| VerfasserIn |
Patrizia Ney, Marius Schmidt, Anne Klosterhalfen, Alexander Graf |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143706
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| Publikation (Nr.) |
 EGU/EGU2017-7455.pdf |
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| Zusammenfassung |
| We present a portable elevator-based setup for measuring CO2, water vapor, temperature and
wind profiles from the soil surface to the surface layer above crop canopies. The end of a tube
connected to a closed-path gas analyzer is continuously moved up and down over the profile
height (currently 2 m), while concentrations are logged at a frequency of 20 Hz. Temperature
and wind speed are measured at the same frequency by a ventilated finewire thermocouple
and a hotwire, respectively, and all measurements are duplicated as a continuous fixed-height
measurement at the top of the profile. Test measurements were carried out at the TERENO
research site of Selhausen (50∘52’09”N, 06∘27’01”E, 104.5 m MSL, Germany,
ICOS site DE-RuS) in winter wheat, winter barley and a catch crop mixture during
different stages of crop development and different times of the day (spring 2015 to
autumn 2016). We demonstrate a simple approach to correct for time lags, and the
resulting half-hourly mean profiles of CO2 and H2O over height increments of 2.5
cm. These results clearly show the effects of soil respiration and photosynthetic
carbon assimilation, varying both during the daily cycle and during the growing
season.
Post-harvest measurements over bare soil and short intercrop canopy (<20 cm) were
analyzed in the framework of Monin-Obukhov similarity theory to check the validity of the
measurement and raw data processing approach. Derived CO2 and latent heat fluxes show a
good agreement to eddy-covariance measurements.
In a next step, we applied a dispersion matrix inversion (modified after Warland and
Thurtell 2000, Santos et al. 2011) to the concentration profiles to estimate the vertical source
and sink distribution of CO2 and H2O. First results showed reasonable values for evaporation,
transpiration and aboveground net primary production, but a likely overestimation of
soil respiration. We discuss possible causes associated with exchange processes
near the soil surface below a dense canopy, and the potential use of the wind and
temperature profiles in efforts to improve the dispersion parametrization in this
region.
Santos, E.A., Wagner-Riddle, C., Warland, J.S. and Brown, S. (2011): Applying a
Lagrangian dispersion analysis to infer carbon dioxide and latent heat fluxes in a corn canopy.
Agricultural and Forest Meteorology 151: 620-632.
Warland, J.S. and Thurtell, G.W. (2000): A Lagrangian solution to the relationship
between a distributed source and concentration profile. Boundary-Layer Meteorology 96:
453-471. |
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