Cross‐correlation analysis of the dynamics of methane emissions from a boreal peatland

Abstract

The effects of temperature, water table, and precipitation on the methane fluxes from a boreal low‐sedge Sphagnum papillosum pine fen were analyzed with statistical cross correlations of daily data. The six measurement sites represented different vegetation surfaces of the mire (hummocks, lawns, and flarks) with increasing moisture. The dynamics were analyzed separately for the early summer (May‐July) and the late summer (August‐October) periods in addition to the whole summer (May‐October) period. Methane emissions increased with increasing peat temperature. During the late summer period, changes in peat temperatures at depths of 20 and 50 cm were reflected in methane emissions within 2 days. The persistently high water tables during the measurement period probably did not reveal the dynamics between water table fluctuations and methane emissions very clearly. Methane emission levels correlated negatively with depths of the water tables, that is, high methane emissions were associated with low water tables and vice versa. The suppression of methane emissions by filling the unsaturated gas space during precipitation and the increased release rate caused by a declining water table could explain the result. Methane emissions correlated positively with changes in water tables, that is, a rise in water table increased methane emissions during the early and whole summer periods. Precipitation increased emissions with a lag from zero to several days throughout the summer. Generally, the estimated responses of methane fluxes to precipitation and changes in water table indicated similar time lags. Methane flux from the flark surfaces seemed to respond rapidly to rainfall and changes in water table with a lag of zero or 1 day. In the lawn‐low hummock, the lawn and one hummock site, methane flux showed a slow response with several days lag. This study strongly indicates that temperature, water table, and precipitation affect methane emissions with complex interactions.