Emission of phosphine in intertidal marshes of the Yangtze Estuary

Emission of phosphine, a gaseous form of P, is presently considered a potential pathway of the P biogeochemical cycle in aquatic sediments. This study investigated the emission fluxes of phosphine and its potential production mechanisms in the intertidal marshes of the Yangtze Estuary. It is shown that the relatively high emission fluxes of phosphine were measured in warm seasons, with the values of 3.85–24.9 ng m−2 h−1 and 4.21–36.5 ng m−2 h−1 in August and September, respectively. In contrast, lower fluxes of phosphine appeared in May (1.23–6.32 ng m−2 h−1) and January (0.21–0.91 ng m−2 h−1). Also, the fluxes of phosphine were generally higher in the freshwater marsh, compared with the brackish marsh. The spatio-temporal pattern of phosphine emissions was observed to be mainly associated with sediment structure, temperature and salinity. Meanwhile, the significant correlations of phosphine emissions with sedimentary P and alkaline phosphatase activities reflect that phosphine probably derives from the microbial transformations of PO4 and organic P. In addition, it is estimated that approximately 1.08 × 106 g of phosphine is released annually from sediments into the pelagic water of the Yangtze Estuary. Therefore, it is concluded that phosphine emissions may be an important internal source of P, making a significant contribution to the occurrence of algal blooms especially during warm seasons.