 |
| Titel |
A comparison of linear and exponential regression for estimating diffusive methane fluxes by closed-chamber - results from laboratory and field campaigns |
| VerfasserIn |
P. Schreiber, I. Forbrich, L. Kutzbach, A. Hormann, U. Wolf, M. Miglovec, M. Pihlatie, J. R. Christiansen, M. Wilmking |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029010
|
|
|
|
|
|
| Zusammenfassung |
| Closed chambers are the most common method to determine methane (CH4) fluxes in
peatlands. The concentration change over time is monitored, and the flux is usually calculated
by the slope of a linear regression function. However, chambers tend to slow down the gas
diffusion by changing the concentration gradient between soil and atmosphere.
Theoretically, this would result in a near-exponential concentration change in the chamber
headspace.
Here, we present data from a laboratory experiment and from two field campaigns on the
basis of which we evaluate flux calculation approaches based either on linear or exponential
regression models. To compare the fit performances of the two models, we used
the Akaike Information Criterion with small sample second order bias correction
(AICc). For checking the quality of flux data, we used the standard deviation of
residuals.
The calibration system in the laboratory experiment used during the chamber calibration
campaign at Hyytiälä Forestry Field Station in August 2008 has been described by Pumpanen
et al. (2004). Five different flux levels on two different soil porosities where tested.
Preliminary results show that most concentration-over-time datasets were best described by
the exponential model as evaluated by the AICc. It appeared that the flux calculation using the
exponential model was better suited to determine the preset fluxes than that using the linear
model.
In the dataset of the first field campaign (April to October 2007) from Salmisuo (Finland,
62.46Ë N, 30.58Ë E), however, the majority of fluxes was best fitted with a linear regression
on all microsite types. Those fluxes which are best fitted exponentially are most probable
due to chamber artefacts. They occurred mostly during a drought period in August
2007, which seemed to increase the artificial impact of the chamber. However,
these results might be site-specific: In Ust-Pojeg (Russia, 61.56Ë N, 50.13Ë E),
where CH4 emissions are supposed to be higher than in Salmisuo, more fluxes (ca.
30% during April to June 2008) were selected to be best fitted with an exponential
regression.
References:
Pumpanen, J., Kolari, P., Ilvesniemi, H., Minkkinen, K., Vesala, T., Niinistö, S., Lohila,
A., Larmola, T., Morero, M., Pihlatie, M., Janssens, I., Curiel Yuste, J., Grünzweig, J. M.,
Reth, S., Subke, J.-A., Savage, K., Kutsch, W., Østreng, G., Ziegler, W., Anthoni,
P., Lindroth, A. & Hari, P. 2004. Comparison of different chamber techniques for
measuring soil CO2 efflux. Agricultural and Forest Meteorology 123, 159-176. |
|
|
|
|
|
|