[Diurnal Variations of CH and NO 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 (CH and NO) 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 CH from the UDP and DP ranged from 0.04 to 0.10 mg·(m·h) and 14.04 to 33.72 mg·(m·h), respectively, with means of (0.07±0.01) mg·(m·h) and (24.74±2.33) mg·(m·h). The CH flux was lower during the day and higher at night with a net flux as the sources of the CH. The fluxes of NO from the UDP ranged from -0.027 to 0.011 mg·(m·h), and the average fluxes of (0.002±0.004) mg·(m·h) showed "weak absorption by day and emission at night." The NO fluxes from the DP were emitted all day (ranging from 0.59 to 1.76 mg·(m·h)) with the average fluxes of NO (1.07±0.15) mg·(m·h) indicating higher fluxes at night and lower fluxes during the day. Our research demonstrated that drainage would significantly enhance CH and NO 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 CH and NO emissions during early winter. Clearly, future measurements at high frequency over a long time and at different spatial scales would be worth researching from drained aquaculture ponds.