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The closed chamber technique is widely used to measure the exchange ofmethane (CH4) and carbon dioxide (CO2) from terrestrialecosystems. There is, however, large uncertainty about which model should beused to calculate the gas flux from the measured gas concentrations. Due toexperimental uncertainties the simple linear regression model (first-orderpolynomial) is often applied, even though theoretical considerations of thetechnique suggest the application of other, curvilinear models.High-resolution automatic chamber systems which sample gas concentrationsseveral hundred times per flux measurement make it possible to resolve thecurvilinear behavior and study the information imposed by the naturalvariability of the temporal concentration changes. We used more than 50 000such flux measurements of CH4 and CO2 from five field siteslocated in peat-forming wetlands ranging from 56 to 78° N toquantify the typical differences between flux estimates of different models.In addition, we aimed to assess the curvilinearity of the concentration timeseries and test the general applicability of curvilinear models. Despitesignificant episodic differences between the calculated flux estimates, theoverall differences are generally found to be smaller than the local fluxvariability on the plot scale. The curvilinear behavior of the gasconcentrations within the chamber is strongly influenced by wind-drivenchamber leakage, and less so by changing gas concentration gradients in thesoil during chamber closure. Such physical processes affect both gas speciesequally, which makes it possible to isolate biochemical processes affectingthe gases differently, such as photosynthesis limitation by chamber headspaceCO2 concentrations under high levels of incoming solar radiation. Weassess the possibility to exploit this effect for a partitioning of the netCO2 flux into photosynthesis and ecosystem respiration as an exampleof how high-resolution automatic chamber measurements could be used forpurposes beyond the estimation of the net gas flux. This shows that whilelinear and curvilinear calculation schemes can provide similar net fluxes,only curvilinear models open additional possibilities for high-resolutionautomatic chamber measurements

Calculations of automatic chamber flux measurements of methane and carbon dioxide using short time series of concentrations