Greenhouse Gas Fluxes from Irish Coastal Wetlands

Coastal wetlands are known for their ability to store large amounts of carbon (C). The C buried in these ecosystems can be offset in the form of greenhouse gas (GHG) emissions, namely from carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Methane and N2O are potent greenhouse gases with sustained-flux global warming potentials 45-times and 270-times that of CO2 over a 100-year period, respectively. The magnitude and variation of these potential offsets remain poorly quantified particularly for temperate European coastal wetlands. There is approximately 4000-6000 hectares of saltmarsh ecosystems in Ireland, and these contain swards of the invasive species Spartina anglica. In addition, there are areas of freshwater peatlands on the Westcoast of Ireland that are vulnerable to sea level rise. This thesis aimed to evaluate temporal GHG fluxes from invasive Spartina anglica, quantify the CO2 uptake ability of an Irish saltmarsh, investigate the impact of tidal inundation on CO2 dynamics, and investigate the effects of saltwater intrusion on coastal freshwater peat carbon dynamics. I conducted a year-long temporal analysis on CH4 and N2O fluxes from invasive Spartina anglica in a Dublin saltmarsh and found that the saltmarsh produced negligible amounts of both GHGs, with uptake seen in many cases. I collected a year’s worth of CO2 flux data using the eddy covariance method from an Irish Atlantic saltmarsh where the saltmarsh acted as a substantial sink to CO2. Tidal inundation was found to be a controlling factor for both ecosystem respiration (CO2 emission) and gross primary productivity (CO2 uptake), suppressing both processes. A month-long mesocosm experiment using intact soil cores was carried out to investigate the impact of water treatment (fresh or salt) and inundation (full or tidal) on soil carbon and GHG dynamics from an Irish coastal freshwater peatland. The mesocosm study integrates the global change factor saltwater intrusion, deepening our understanding of the potential detrimental effects of increased storm surges and sea level rise on freshwater peat C stores. The combination of these studies provides an insight into temporal coastal wetland atmospheric GHG flux dynamics while integrating global change factors, bridging key knowledge gaps on temperate coastal wetland GHG and C dynamics. This research highlights the key role Irish coastal wetlands play in climate regulation as well as the detrimental impact that saltwater intrusion has on peatland carbon storage, providing essential baseline knowledge which can inform policy makers and land managers aiming to manage coastal wetlands for GHG mitigation.