Fig 1.
The location of flux tower in the Robinsons pasture, western Newfoundland, Canada (48.264 N, 58.665 W).
The image is similar, but not identical, to the original image, and therefore is only for illustrative purposes. The outline of the site was indicated by the red solid line and the red pin represents the location of eddy covariance (EC) tower (a); (b) a photo of the setup of EC measurement system.
Fig 2.
Footprint versus wind direction for different periods in the two study years.
The legends indicate the cumulative footprint where 70% flux were originated. The yellow, purple and blue boxes indicate varying distances from the tower where the 70% of CH4 fluxes were originated.
Table 1.
Comparison of monthly average temperature and cumulative monthly rainfall measured at Robinson Pasture during measurement periods from April, 2014 to May, 2016 with the long-term (1981–2010 average ± SD) measurements from the nearby climate station in Stephenville, Newfoundland and Labrador.
Fig 3.
The daily average air temperature (a1-a3), soil temperature at 10 cm and 50 cm (b1-b3), photosynthetic photon flux density (PPFD) (c1-c3), volumetric soil water content at depth of 10 cm (d1-d3), water table level (e1-e3) and cumulative rainfall (f1-f3) during the measurement periods.
Table 2.
Average daily air temperature, soil temperature at depth of 10 cm and 50 cm, photosynthetic photon flux density (PPFD), cumulative rainfall, and water table position for four different periods.
Negative values indicate water table was below the peatland surface.
Fig 4.
The daily average CH4 flux (a), five-day running average CH4 flux (b), five-day running average water table level (c) and five-day running average soil temperature at 50 cm (d) of different periods during the two study years.
Table 3.
Total accumulated CH4 fluxes, their uncertainties (g CH4 m-2) for the different study periods and contributions to the annual emissions in two years from May 2014 to April 2016.
RU, GU and TU in the table indicate random uncertainty, uncertainty due to gap filling and total uncertainty, respectively.
Fig 5.
The cumulative gap-filled CH4 flux during the two study years (from May 2014 to April 2016).
Table 4.
The results of stepwise multivariable regression analysis between daily average CH4 flux and abiotic variables including friction velocity (u*), vapor pressure deficit (VPD), photosynthetically active photon flux density (PPFD), air temperature (Ta), soil temperature at 10 cm and 50 cm (T10, T50), soil water content at 10 cm and 50 cm (SWC10, SWC50) and water table level (WT) and biotic variables such as gross primary productivity (GPP) and net ecosystem exchange (NEE).
Only significant (P<0.05) variables were included in the equation. No significant interactions among the variables were found (P>0.05), and the variance inflation factor (VIF) for all variables in the model is less than 5.
Table 5.
Comparison of accumulated methane flux balance for agriculturally managed peatlands and natural peatlands.