Importance of sediment organic matter to methane ebullition in a sub-tropical freshwater reservoir

Alistair Grinham; Matthew Dunbabin; Simon Albert

doi:10.1016/j.scitotenv.2017.10.108

Importance of sediment organic matter to methane ebullition in a sub-tropical freshwater reservoir

Sci Total Environ. 2018 Apr 15:621:1199-1207. doi: 10.1016/j.scitotenv.2017.10.108. Epub 2017 Oct 18.

Authors

Alistair Grinham¹, Matthew Dunbabin², Simon Albert³

Affiliations

¹ School of Civil Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. Electronic address: a.grinham@uq.edu.au.
² Institute for Future Environments, Queensland University of Technology, Brisbane, QLD 4001, Australia.
³ School of Civil Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia.

PMID: 29054653
DOI: 10.1016/j.scitotenv.2017.10.108

Abstract

This paper summarises the results of an extensive field campaign which demonstrates that high sediment organic matter is the primary driver of methane ebullition in a sub-tropical, freshwater reservoir. Methane emissions from freshwater reservoirs represent an important global methane source. Whilst diffusive methane fluxes are commonly used for predicting total emissions, recent studies show that the under-reported ebullitive fluxes can vary by over three orders of magnitude within an individual system and have a greater relative contribution compared to diffusion. Key to predicting this variability in emission rates is to better understand the primary drivers of different emission pathways, and in particular ebullition. Zones of catchment derived organic material as well as elevated water column chlorophyll a concentration have been associated with increased rates of ebullition. Little Nerang Dam (LND), a subtropical freshwater reservoir in Queensland Australia, consistently experiences high rates of ebullition adjacent to major inflow arms that are both deposition zones of catchment organic material as well as areas with elevated water column chlorophyll a concentration. A year-long study of emission rates was undertaken on LND during which water column chlorophyll a concentration, bottom water temperature and sediment organic matter content were assessed for methane ebullition potential. This included a transect with high-spatial sampling (259 sites) from the dam wall to the ebullition zones to explore the relationship between water column chlorophyll a concentration, sediment organic matter content and methane ebullition. These results showed that ebullition was associated with the large forest litter deposits adjacent to major inflow sites where sediment organic matter content was significantly higher compared with the main body of the reservoir.

Keywords: Australia; Ebullition; Freshwater reservoir; Methane; Sub-tropics.