A novel reduced-complexity approach for modelling ebullition in peatlands.

Methane (CH4) is a greenhouse gas with a global warming potential much greater than carbon dioxide, and one of the major sources of naturally occurring CH4 are peatlands. Large amounts of CH4 can be transported from peat to the atmosphere through bubbles (ebullition). The exact controls of ebullition remain uncertain, but evidence suggests that physical processes related to gas transport and storage within the peat structure is important. Although these processes are key to replicating ebullition, no computer models of ebullition contain a detailed spatial representation of the peat structure.
This thesis investigated the role of peat structure on CH4 ebullition using computer and physical models. A computer model of ebullition was developed and tested against physical models of ebullition. The computer model contained a spatial representation of peat and rules to transport gas through the peat structure. Physical models consisted of i.) air injected into a simple porous medium, and ii.) a separate physical model with peat. Following a pattern oriented modelling approach, gas storage, bubble size, and bubble release (ebullition) were three patterns used to test the computer model. Overall the computer model was able to replicate the patterns generated from the physical models and this demonstrated that the computer model was useful for modelling CH4 ebullition from peat. The results generated with the computer model confirmed our hypothesis: peat structure and subsequent gas storage were found to be important controls on ebullition timing location and quantity. From these results, we were able to make recommendations on sampling CH4 ebullition from peat in the field.