USING WAVELETS TO IDENTIFY HYDRAULIC HEAD ANOMALIES ASSOCIATED WITH METHANE EBULLITION EVENTS

Temporal patterns in multi-year hydraulic head time series data sets, collected at 2 minute intervals in Caribou Bog (central Maine), were identified using stationary wavelet analysis, This analysis reveals both low and high frequency hydraulic head fluctuation at different depths within Caribou Bog, a 2500 hectare peatland in central Maine. Daily oscillations in hydraulic head, associated with higher daytime evapotranspiration or snow melt, are isolated by wavelet analysis. Unusual high frequency oscillations are apparent in these data that are hypothesized to be associated with biogenic gas movement. The frequent high frequency hydraulic head fluctuations are identified shortly after well installation and during other research activities, indicating that early data is impacted by disturbance. Later high frequency data anomalies are synchronous with water pressure changes, with centimeter-scale high frequency oscillations occurring shortly after or during changes in water levels and atmospheric pressure associated with rain events, daily evapotranspiration cycles, and snow melt. Deep peat head anomalies are often associated with anomalies in shallower wells, suggesting these events are larger or gas is rapidly migrating through the entire peat column. Our data suggests that gas is generated in both shallow and deep peat, with more frequent ebullition events originating in shallow peat and less frequent (but potentially larger) events originating in deep peat. The timing of these events is influenced by hydraulic forcing within the peat column.