Diffusive CH₄ fluxes from aquaculture ponds using floating chambers and thin boundary layer equations

Static floating chambers (FCs) are the conventional method to measure CH₄ fluxes across the water-air interface in ponds, while thin boundary layer (TBL) modelling is increasingly used to estimate CH₄ fluxes. In this study, both FCs measurements and TBL models of gas transfer velocity were used to determine CH₄ evasion from aquaculture ponds in southeastern China. The surface water CH₄ concentrations ranged from 0.4 to 9.1 μmol L-1 with an average of 4.8 ± 0.8 μmol L-1. CH₄ flux was always positive, indicating the ponds as a persistent CH₄ source to air. Mean CH₄ flux based on different TBL models showed large variations, ranging between 19 and 316 μmol m⁻² h⁻¹. Compared against the direct measurement FCs, three TBL models developed for the open sea, flowing estuarine system and lentic ecosystem (TBL_W92a, TBL_RC01, and TBL_CL98, respectively) overestimated CH₄ emission by 40–200%, while the wind tunnel-based TBL model (TBL_LM86) underestimated CH₄ emission. Two TBL models developed for lakes (TBL_W92b and TBL_CW03) gave estimates similar to FCs.