Document Detail

Advection and resulting CO2 exchange uncertainty in a tall forest in central Germany.
MedLine Citation:
PMID:  18767618     Owner:  NLM     Status:  MEDLINE    
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.
Werner L Kutsch; Olaf Kolle; Corinna Rebmann; Alexander Knohl; Waldemar Ziegler; Ernst-Detlef Schulze
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Ecological applications : a publication of the Ecological Society of America     Volume:  18     ISSN:  1051-0761     ISO Abbreviation:  Ecol Appl     Publication Date:  2008 Sep 
Date Detail:
Created Date:  2008-09-04     Completed Date:  2008-12-31     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9889808     Medline TA:  Ecol Appl     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1391-405     Citation Subset:  IM    
Max-Planck-Institute for Biogeochemistry, P.O. Box 10 01 64, 07701 Jena, Germany.
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MeSH Terms
Air Movements*
Carbon Dioxide / analysis*,  metabolism
Environmental Monitoring / methods*
Models, Theoretical
Trees / metabolism*
Reg. No./Substance:
124-38-9/Carbon Dioxide

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