Three Gorge Dam Reservoir (TGDR) is a new forming ecosystem and its sediments dynamics remains unknown. Investigation on the nitrification and denitrification dynamics of sediments of TGDR during water collection and release events-anti-seasonal actions-is critical for nitrogen management in TGDR. In this study, we sampled sediments in three locations (upstream, center, and downstream along water flow) of South River, located in a typical small tributary, Nanhe, in TGDR during 2015 water collection and release events to characterize its physiochemical property and determine its nitrification and denitrification rates using acetylene inhabitation method. The results showed that the concentrations of physiochemical parameters of sediments (total carbon, total nitrogen, nitrate, and ammonia) were significantly higher (P<0.05) in water collection event than those in water release event, suggesting there were external materials (e. g., soil) entering into TGDR. Furthermore, the nitrification rate of sediments in water collection event[194.06 μmol·(m2·h)-1] was significantly higher than that in water release event[16.52 μmol·(m2·h)-1]. Sediments nitrification rate was positively correlated to the physiochemical parameters. In contract, the denitrification rate of sediments was higher in water release event[647.20 μmol·(m2·h)-1] than that in water collection event[24.04 μmol·(m2·h)-1). Accordingly, the denitrification rate of sediments was negatively correlated to the physiochemical parameters.
Keywords: Three Gorge Dam Reservoir; denitrification rate; nitrification rate; sediments; small tributary; water collection period; water release period.