Spatial and temporal variation of CO2 and CH4 emissions from a septic tank soakaway

Celia Somlai; Jan Knappe; Laurence Gill

doi:10.1016/j.scitotenv.2019.04.449

Spatial and temporal variation of CO₂ and CH₄ emissions from a septic tank soakaway

Sci Total Environ. 2019 Aug 20:679:185-195. doi: 10.1016/j.scitotenv.2019.04.449. Epub 2019 May 5.

Authors

Celia Somlai¹, Jan Knappe², Laurence Gill³

Affiliations

¹ Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, The University of Dublin, Ireland. Electronic address: celia.somlai@tcd.ie.
² Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, The University of Dublin, Ireland; MACSI, University of Limerick, Ireland. Electronic address: jan.knappe@tcd.ie.
³ Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, The University of Dublin, Ireland. Electronic address: laurence.gill@tcd.ie.

PMID: 31082592
DOI: 10.1016/j.scitotenv.2019.04.449

Abstract

CO₂ and CH₄ flux measurements over a septic tank soakaway located in a northern maritime climate (Ireland) were conducted for a period of 81 days using a multi-chamber automated soil gas flux chamber system with high spatial and temporal resolution. Overall median CO₂ fluxes were 7.28; 6.40 μmol CO₂ m^-2 s^-1 from the soakaway and control soil, respectively. Overall median CH₄ fluxes were - 0.28; -0.67 nmol CH₄ m^-2 s^-1 from the soakaway and control soil, respectively. While CO₂ fluxes expressed strong diurnal variability driven by soil temperature, CH₄ fluxes were less affected by environmental factors and effectively limited to the first few meters from the septic tank. However, localised CH₄ degassing events were observed during drying conditions with up to 60-times higher fluxes compared to the overall median. The soakaway was found to be a net emitter of both CO₂ and CH₄, releasing a total of 7.327 kg CO₂ yr^-1 and 0.033 kg CO_2Eq. yr^-1, respectively. The apparent spatio-temporal heterogeneity of observed soil gas fluxes identified in this study emphasises the importance of integrating measurements with both high spatial and temporal resolution from on-site installations as engineered nature-based solutions.

Keywords: Anthropogenic greenhouse gas emissions; Carbon dioxide; Methane; On-site wastewater treatment system; Soil flux chamber.