Validation of a minimum microclimate disturbance chamber for net ecosystem flux measurements
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| Title: | Main Title: Validation of a minimum microclimate disturbance chamber for net ecosystem flux measurements |
| Description: | Abstract: A minimum-disturbance chamber for canopy net CO2 and H2O flux measurements is described. Thesystem is a passively (optionally actively) ventilated tunnel with large (similar to 0.14 m2) in- and outletcross sections covering a surface area of approximately 1.6 m2. A differential, non-drying closed-path gasanalyzer is used to minimize the requirement for concentration build-ups or drawdowns between the inandoutlet, and 0.05 mm thick FEP (fluorinated ethylene propylene) film is used as top and wall materialto minimize radiation modifications.First measurement results in passively ventilated mode are presented from two different sites: awheat field at a lowland site in the westernmost part of Germany, and differently cropped adjacentfields in the Pyrenee foothills in France, including grassland and a cereal-dominated crop mixture forfodder production. Flux estimates derived from measurements over 20–30 min deployments were comparedto concurrent observations by three eddy covariance (EC) stations. The system compared wellto EC measurements, with bias of−6.6% for latent heat flux and +9.0% for CO2 flux (R2 = 0.78 and 0.74,respectively).The presence of the chamber causes a reduction of less than 4% in incoming shortwave radiation, andan increase of about 18% in downward longwave radiation. Near the outlet, CO2 concentration was onaverage modified by−3% with respect to outside conditions, water vapour concentration by +22%, andtemperature by +0.9 K, staying below published modifications of a comparable non-steady-state chamberclosed for 2 min. Ventilation speed varied by less than 9% across the inlet cross section. Limitations includea minimum wind speed requirement that can be set as low as 0.2 m s−1 for a raw data logging frequencyof 1 s−1 or higher, but would need to be higher for slow-response gas analyzers. At the same time, ameasurement period of 10 min or more is recommended to minimize random errors from storage termfluctuations. A correction for the added water vapour volume by evapotranspiration is derived and tested,which typically affects H2O flux itself by less than +2% and CO2 flux measurements by 1 [1]mol/J latentheat. |
| Identifier: | 10.1016/j.agrformet.2013.02.001 (DOI) |
Responsible Party
| Creators: | Alexander Graf (Author), J. Werner (Author), Matthias Langensiepen (Author), Anneke van de Boer (Author), Marius Schmidt (Author), Moritz Kupisch (Author), Harry Vereecken (Author) |
| Publisher: | Elsevier |
| Publication Year: | 2013 |
Topic
| TR32 Topic: | Vegetation |
| Related Subproject: | B5 |
| Subjects: | Keywords: CO2, Eddy Covariance, Evapotranspiration, H2O, Chamber |
File Details
| Filename: | 2013_Graf_AFM.pdf |
| Data Type: | Text - Article |
| Size: | 14 Pages |
| File Size: | 1.5 MB |
| Date: | Accepted: 05.02.2013 |
| Mime Type: | application/pdf |
| Data Format: | |
| Language: | English |
| Status: | Completed |
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| Download Permission: | Only Project Members |
| General Access and Use Conditions: | For internal use only |
| Access Limitations: | For internal use only |
| Licence: | [TR32DB] Data policy agreement |
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Specific Information - Publication
| Publication Status: | Published |
| Review Status: | Peer reviewed |
| Publication Type: | Article |
| Article Type: | Journal |
| Source: | Agricultural and Forest Meteorology |
| Source Website: | www.elsevier.com/locate/agrformet |
| Volume: | 174-175 |
| Number of Pages: | 14 (1 - 14) |
Metadata Details
| Metadata Creator: | Alexander Graf |
| Metadata Created: | 02.12.2013 |
| Metadata Last Updated: | 02.12.2013 |
| Subproject: | B5 |
| Funding Phase: | 2 |
| Metadata Language: | English |
| Metadata Version: | V50 |
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| Page Visits: | 1023 |
| Metadata Downloads: | 0 |
| Dataset Downloads: | 2 |
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