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

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 C(H)4 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.