Timescale dependence of environmental controls on methane efflux from Poyang Hu, China

Abstract. Lakes are an important natural source of CH₄ to the atmosphere. However, the multi-seasonal CH₄ efflux from lakes has been rarely studied. In this study, the CH₄ efflux from Poyang Hu, the largest freshwater lake in China, was measured monthly over a 4-year period by using the floating-chamber technique. The mean annual CH₄ efflux throughout the 4 years was 0.54 mmol m⁻² day⁻¹, ranging from 0.47 to 0.60 mmol m⁻² day⁻¹. The CH₄ efflux had a high seasonal variation with an average summer (June to August) efflux of 1.34 mmol m⁻² day⁻¹ and winter (December to February) efflux of merely 0.18 mmol m⁻² day⁻¹. The efflux showed no apparent diel pattern, although most of the peak effluxes appeared in the late morning, from 10:00 to 12:00 CST (GMT + 8). Multivariate stepwise regression on a seasonal scale showed that environmental factors, such as sediment temperature, sediment total nitrogen content, dissolved oxygen, and total phosphorus content in the water, mainly regulated the CH₄ efflux. However, the CH₄ efflux only showed a strong positive linear correlation with wind speed within 1 day on a bihourly scale in the multivariate regression analyses but almost no correlation with wind speed on diurnal and seasonal scales.