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  Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany

Kutsch, W. L., Kolle, O., Rebmann, C., Knohl, A., Ziegler, W., & Schulze, E. D. (2008). Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany. Ecological Applications, 18(6), 1391-1405.

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 Creators:
Kutsch, W. L.1, Author           
Kolle, O.2, Author           
Rebmann, C.1, Author           
Knohl, A.1, Author           
Ziegler, W.1, Author           
Schulze, E. D.1, Author           
Affiliations:
1Department Biogeochemical Processes, Prof. E.-D. Schulze, Max Planck Institute for Biogeochemistry, Max Planck Society, ou_1497751              
2Service Facility Field Measurements & Instrumentation, O. Kolle, Max Planck Institute for Biogeochemistry, Max Planck Society, ou_1497769              

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Free keywords: Advection Carbon balance Eddy covariance Katabatic fluxes Tall vegetation Undisturbed forests Net ecosystem exchange Surface-air exchange Micrometeorological observations Eddy covariance Soil respiration Complex terrain Carbon Fluxes Vegetation Sites
 Abstract: Potential losses by advection were estimated at Hainich Forest, Thuringia, Germany, where the tower is located at a gentle slope. Three approaches were used: (1) comparing nighttime eddy covariance fluxes to an independent value of total ecosystem respiration by bottom-up modeling of the underlying processes, (2) direct measurements of a horizontal CO2 gradient and horizontal wind speed at 2 m height in order to calculate horizontal advection, and (3) direct measurements of a vertical CO2 gradient and a three-dimensional wind profile in order to calculate vertical advection. In the first approach, nighttime eddy covariance measurements were compared to independent values of total ecosystem respiration by means of bottom-up modeling of the underlying biological processes. Turbulent fluxes and storage term were normalized to the fluxes calculated by the bottom-up model. Below a u(*) threshold of 0.6 m/s the normalized turbulent fluxes decreased with decreasing u(*), but the flux to the storage increased only up to values less than 20% of the modeled flux at low turbulence. Horizontal advection was measured by a horizontal CO2 gradient over a distance of 130 m combined with horizontal wind speed measurements. Horizontal advection occurred at most of the evenings independently of friction velocity above the canopy. Nevertheless, horizontal advection was higher when u(*) was low. The peaks of horizontal advection correlated with changes in temperature. A full mass balance including turbulent fluxes, storage, and horizontal and vertical advection resulted in an increase of spikes and scatter but seemed to generally improve the results from the flux measurements. The comparison of flux data with independent bottom-up modeling results as well as the direct measurements resulted in strong indications that katabatic flows along the hill slope during evening and night reduces the measured apparent ecosystem respiration rate. In addition, anabatic flows may occur during the morning. We conclude that direct measurements of horizontal and vertical advection are highly necessary at sites located even on gentle hill slopes. [References: 56]

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 Dates: 2008
 Publication Status: Issued
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Title: Ecological Applications
Source Genre: Journal
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Publ. Info: Tempe, AZ : Ecological Society of America
Pages: - Volume / Issue: 18 (6) Sequence Number: - Start / End Page: 1391 - 1405 Identifier: CoNE: https://pure.mpg.de/cone/journals/resource/954925593483
ISSN: 1051-0761