Thesis
Unravelling the drivers of greenhouse gas emissions in Australian estuaries (Abstract & Citation only)
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2021
Metrics
59 Record Views
Abstract
Estuaries emit significant amounts of greenhouse gases (CO2, CH4, and N2O) through the processing of riverine and terrestrial organic matter as it travels towards the ocean. However, little is known about how emissions and their drivers differ with estuary type and disturbance. This study investigates the effect of geomorphology and whole-system disturbance on greenhouse gas emissions from Australian estuaries.
High-resolution underway CO2, CH4, and N2O measurements were taken in 36 estuaries across Australia under similar summer (dry) conditions and combined with similar, published data from 11 additional estuaries, encompassing three estuary types and four disturbance levels. Lagoons were a net N2O sink and a net source of CO2 and CH4. Small deltas and tidal systems were net sources of CO2, CH4, and N2O. The highest water-air fluxes were from small deltas for CO2 and N2O and lagoons for CH4. Greenhouse gas emissions increased with disturbance, but the impact of disturbance differed between estuary types.
In lagoons, reduced hydrological connectivity with adjacent environments extended organic matter availability, and seagrasses reduced CO2 concentration via photosynthetic uptake and reduced N2O concentrations by drawing down dissolved inorganic nitrogen. Increasing disturbance resulted in seagrass loss and increased N2O yield. In small deltas and tidal systems, stronger tidal exchange influenced emissions. In small deltas, moderate lateral exchange increased CO2 emissions and moderate tidal flushing decreased organic matter availability, subsequently limiting CH4 emissions. Increased catchment nitrogen inputs enhanced N2O emissions. In tidal systems, with large tidal ranges, greater marine exchange likely reduced organic matter availability and lowered CH4 and N2O emissions. High CO2 emissions in tidal systems likely reflected respiration of increased carbon input from shoreline (e.g. mangroves) and riverine sources.
Australian estuaries have 26% higher water-air CO2 flux than estuaries globally, likely due to lower freshwater flow and, therefore, longer water residence times and higher organic matter availability. Lower mean CH4 (33% less) and median N2O (97% less) water-air fluxes than global estuarine emissions mainly reflected lower disturbance pressures in estuaries and catchments, which reduced overall carbon and nitrogen loads. Annually, Australian estuaries contribute more CO2 (7 to 11%), and less CH4 (1.34%) and N2O (0.07 to 0.54%) to global emissions than expected for their 2.35% contribution to global estuarine surface area. Tidal systems were the largest source of annual greenhouse gas emissions in Australia due to their large surface area.
This study highlights the importance of including a range of estuarine geomorphic types and disturbance levels when making global estimates of estuarine greenhouse gas emissions. Global estuarine greenhouse gas emissions could be better constrained by developing a globally applicable disturbance classification scheme, and further sampling across a range of estuaries at different disturbance levels.
Details
- Title
- Unravelling the drivers of greenhouse gas emissions in Australian estuaries (Abstract & Citation only)
- Creators
- Jacob Yeo
- Contributors
- Bradley D Eyre (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Comment
- (Abstract & Citation only)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Identifiers
- 991013130111102368
- Copyright
- © Jacob Yeo 2021
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis