Title:

The effect of a land-use gradient and sediment characteristics on methane ebullition in four headwater streams

The global atmospheric methane budget is highly affected by freshwater systems. There has been extensive research on methane contributions from lakes and wetlands such that we know wetlands are the dominated natural source of methane, about 75%, but little has been focused on streams and rivers. The bubbling of methane gas from waterbody sediments to the surface is known as ebullition. This emission pathway may account for 10-80% of transport. However, this process is overlooked based on the numerous drivers that affect the spatial and temporal variability of the data as well as the assumption that dissolved transport is the dominant transport process. This research further investigated the drivers of methane ebullition in streams during the summer months, May through August, at four locations in Massachusetts and New Hampshire. There were two forested sites, Cart Creek in Massachusetts and Dube Brook in New Hampshire as well as two urban sites, Sawmill Brook in Massachusetts and College Brook in New Hampshire, to create a land-use gradient across the streams. This gradient was observed by analyzing the sediment characteristics in the streams as human activity may influence the type of sediment that is deposited. Inverted-funnel bubble traps were utilized to collect ebullitive methane gas and sediment corers were used to collect stream sediment to analyze the conditions for methanogenesis-favorable conditions. These methods were done to inspect the spatial variables that may control and influence methane ebullition in streams. Collected methane was analyzed using a gas chromatograph to obtain a concentration and the sediment was put through numerous processes to obtain depth, percent organic matter and bulk density. Analysis of the data showed that both the land-use gradient as well as the sediment characteristics did not have an effect on the methane flux via ebullition across these four streams as there may be other possible drivers that have an influence on this process.

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