Changes in Greenhouse Gas Emissions from Onsite Wastewater Treatment Systems Due to Climate Change.

Climate change may affect the composition and amount of greenhouse gases (GHG) emitted from the soil treatment area (STA) of onsite wastewater treatment systems (OWTS) in the Northeastern United States. Higher temperatures and water tables can affect treatment by reducing the volume of unsaturated soil and oxygen available for treatment, which may result in greater production of GHGs or a shift towards more potent GHGs (e.g. CO₂ à CH₄), and increasing the global warming potential. We used intact soil mesocosms to quantify the impact of climate change (30 cm elevation in water table, 5°C increase in soil temperature) on the GHG emissions from a conventional and two types of shallow narrow STAs. Conventional STAs receive wastewater from the septic tank, with infiltration occurring deeper in the soil profile. In contrast, shallow narrow STAs receive pre-treated wastewater that infiltrates higher in the soil profile.  Greater production of methane and carbon dioxide were observed from all STA types under climate change, however the increase was more pronounced in the conventional STA.  Production of nitrous oxide decreased under climate change for all STA types, however, the decrease was more pronounced in the shallow narrow STAs.  This may indicate a change in speciation of nitrogen gas from nitrous oxide to dinitrogen gas under climate change.  Under climate change the global warming potential due to GHG release increased for the conventional STAs, but decreased for the shallow narrow STAs.  Our results indicate that climate change can affect production and speciation of GHGs, with effects dependent on the gas and STA type.