Resolving the organic carbon budget of a humic, oligotrophic lake in the west of Ireland

• Main Author: Doyle, Brian C.
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Biology; Chemistry; Physics; North Atlantic; North Atlantic oscillation
• Online Access: http://eprints.dkit.ie/760/

Waters draining peatland catchments are generally coloured due to high levels of dissolved and particulate organic carbon (DOC and POC). This flux represents a key link between soil and ocean carbon pools and fuels the aquatic food-web. Knowledge about these carbon fluxes is crucial to broaden our understanding of global C cycling. In three interconnected studies, the dynamics of aquatic carbon cycling were explored in the Burrishoole catchment (Ireland) and its main lake, Lough Feeagh. In the first study, changes in river water colour (a DOC proxy) were analysed in three streams feeding Lough Feeagh. Statistical analysis revealed that three variables, soil temperature, soil moisture deficit, and the North Atlantic Oscillation, explained 66% of colour variance. In the second study, high-frequency measurements of CO2, in the surface waters of Lough Feeagh, were examined along with a set of environmental variables. CO2 concentrations ranged between 491 and 1169 µatm, and the lake was a constant source of CO2 to the atmosphere. Statistical analysis revealed that inflow DOC concentration explained 68% of the CO2 variability. An organic carbon (OC) budget for Lough Feeagh during 2017 was estimated in the third study. The total OC load to the lake was 2544 t C (equivalent to 817 g m2 yr-1 of lake area), of which 51% was transported as DOC, and 41% as POC, 4% in ground water, 3% as net ecosystem production, and 1% in rainwater. The total OC fate was estimated to be 2689 t C (equivalent to 864 g m2 yr-1 of lake area) of which 49% and 12% were exported as DOC and POC respectively, 28% was deposited as sediment and 11% was emitted as CO2 to the atmosphere. These studies provided an improved understanding of the quantity of OC in flux and insights into the mechanisms driving these fluxes