Diurnal Variations of CH4 and N2O Fluxes from the Drained Aquaculture Pond in the Minjiang River Estuary During Early Winter

: Annual drainage is a typical management activity practiced by operators as a way to export aquaculture effluent, accelerate aerobic decomposition of bottom soils, and avoid eutrophication during the non-culture period after harvest. Drainage activities can cause large changes in hydrology, nutrient cycling, sediment physicochemical properties, and even broad ecosystem functions. In order to understand the effects of drainage on the diurnal variation characteristics and magnitude of greenhouse gas (CH4 and N2O) fluxes from the aquaculture ponds of the estuaries, a 24-hour continuous monitoring was conducted from one undrained pond (UDP) and one drained pond (DP) during early winter in the Minjiang River estuary on the southeast coast of China. Over the entire study period, the fluxes of CH4 from the UDP and DP ranged from 0.04 to 0.10 mg·(m2·h)-1 and 14.04 to 33.72 mg·(m2·h)-1, respectively, with means of (0.07±0.01) mg·(m2·h)-1 and (24.74±2.33) mg·(m2·h)-1. The CH4 flux was lower during the day and higher at night with a net flux as the sources of the CH4. The fluxes of N2O from the UDP ranged from -0.027 to 0.011 mg·(m2·h)-1, and the average fluxes of (0.002±0.004) mg·(m2·h)-1 showed "weak absorption by day and emission at night." The N2O fluxes from the DP were emitted all day (ranging from 0.59 to 1.76 mg·(m2·h)-1) with the average fluxes of N2O (1.07±0.15) mg·(m2·h)-1 indicating higher fluxes at night and lower fluxes during the day. Our research demonstrated that drainage would significantly enhance CH4 and N2O release from the aquaculture ponds. The study also preliminarily confirms that the undrained pond converted to a drained pond considerably alter the diurnal variation characteristics of the CH4 and N2O emissions during early winter. Clearly, future measurements in situ at high frequency over a long time and at different spatial scales would be worth researching from drained aquaculture ponds.