Environment Gradient related Dissimilatory Nitrate Reduction to Ammonium in Huangmao Sea Estuary: Rates and Community Diversity

Abstract. The potential rates of dissimilatory nitrate reduction to ammonium (DNRA) in the sediments collected from Huangmao Sea Estuary (HSE), one of Pearl River Estuaries in China, were investigated. The research covers a one-year period at 20 sites of HSE based on the ¹⁵N isotope and molecular biology analysis. The results showed that the environment gradients of nitrogen pollutants decreased from the estuary to the sea, and the characteristics of terrestrial pollutant export were obvious. ¹⁵NH₄⁺ was detected in all sites in continuous-flow systems, which showed that DNRA existed in HSE potentially. In which the maximum ¹⁵NH₄⁺ was 1948.5 μg/L, accordingly in situ rate of DNRA was 6.3 μg/L.h in 72 h. The high transcripts of nrfA gene were found at the same site, with values of 1 159 715 copics/(g wet sediment). Correspondingly, a very low transcripts of nrfA were found at other sites. Principal components analysis (PCA) based on community composition at genus level showed the distribution pattern of the nrfA gene sequences. Nine samples formed three distinct clusters, corresponding to their geographical locations, which suggested that salinity was likely to affect the selection of the nrfA bacterial populations. This study provide a better understanding of DNRA in the Pearl River Estuary.