Development and field application of a low-cost device for sampling greenhouse gas fluxes at the air-water interface in limnological studies

Desenvolvimento e aplicação de dispositivo de baixo custo para a amostragem de fluxos de gases de efeito estufa na interface ar-água em estudos limnológicos

Abstract

Aim  The objective of the present study was to develop and field-apply a simple device for sampling greenhouse gas flows (CO₂ and CH₄) at the air-water interface.

Methods  The device consisted of a cylindrical chamber made of high-density polyethylene with a valve to collect gases. The chamber sealing materials (silicone rubber and epoxy resin) and the system configuration (area/volume ratio A/V, and influence of ventilation) were evaluated. The device was applied in five field campaigns (n = 45). The samples were stored in gasometric containers until analysis by gas chromatography with flame ionization detection.

Results  The epoxy resin sealed the chambers better, while the non-vented device with a higher A/V ratio showed better mixing with fewer uncertainties in gas diffusion through boundary layer disturbance. The flow rates of the target gases varied greatly, from below the limit of quantification for CH₄ (< 0.062 mg m^-2 min^-1) to 0.214 mg m^-2 min^-1, and from 0.3 to 42.3 mg m^-2 min^-1 for CO₂.

Conclusions  These chambers minimize disturbances to the water body and the natural gas exchange processes obtaining more representative data on the natural emissions. Our floating chamber device proved robustness and versatility for determining gas flows at the air-water interface. However, its use must be evaluated in preliminary field work to define the sampling interval time, uncertainties and main analytical challenges to be overcome.

Keywords:
carbon dioxide (CO₂); diffusive chamber; GHGs; methane (CH₄); wastewater pollution

Graphical Abstract