Silver nanoparticles inhibit nitrification but enhance nitrous oxide production by nitrifying organisms.

Global reactive nitrogen (N) has increased dramatically in coastal marine ecosystems over the past decades and caused numerous eco‐environmental problems. Coastal marine sediment plays a critical role in N losses via denitrification and anaerobic ammonium oxidation (anammox) and release of nitrous oxide (N2O). However, both the magnitude and contributions of denitrification, anammox, and N2O production in sediments still remain unclear, causing uncertainty in defining the N budget for coastal marine ecosystems. Here potential rates of N losses, and their contributions and controlling factors, were investigated in surface sediments during six cruises from 429 sites of the East China Sea. The potential rates of denitrification, anammox, and N2O production varied both spatially and seasonally, but the contribution of anammmox to total N2 production (%anammox) and N2O:N2 ratio only varied spatially. Both organic carbon and nitrate (NO3−) were important factors controlling N losses, N2O:N2 ratio, and %anammox. Our results also showed that marine organic carbon induced by eutrophication plays an important role in stimulating reactive N removal and increasing N2O production in warm seasons. The sediment N loss caused by denitrification, anammox, and N2O production in the study area were estimated at 2.2 × 106 t N yr−1, 4.6 × 105 t N yr−1, and 8 × 103 t N yr−1, respectively. Although sediments remove large quantities of reactive N, they act as an important source of N2O in this region influenced by NO3−‐laden rivers.

No abstract

No abstract

Ammonium (NH4+) pollution and associated processes causing environmental problems in aquatic ecosystems have attracted much attention. However, the microbial pathways of NH4+ production and removal and associated influencing factors in the sediments of urban rivers remain unclear. In this study, microbial pathways of NH4+ production and removal were quantified to examine the NH4+ balance in the sediments of Shanghai river networks. The results indicated that potential rates of gross nitrogen mineralization, dissimilatory nitrate reduction to ammonium, and nitrogen fixation ranged from 0.25 to 25.83 μg N g−1 d−1, from undetectable to 3.47 μg N g−1 d−1, and from 0.07 to 3.05 μg N g−1 d−1, respectively. The potential rates of gross NH4+ immobilization, anammox, and nitrification, as the NH4+ removal processes, ranged from 0.24 to 26.27 μg N g−1 d−1, from 0.01 to 7.97 μg N g−1 d−1, and from 0 to 9.62 μg N g−1 d−1, respectively. Temperature, dissolved oxygen, NO3−, NH4+, and total organic carbon had great influences on these NH4+ production and removal processes. In addition, the total amounts of NH4+ production and removal through microbial pathways in sediments of Shanghai river networks were estimated at approximately 2.6 × 105 t N yr−1 and 3.9 × 105 t N yr−1, respectively. Thus, the net sink of NH4+ was 1.3 × 105 t N yr−1, which accounts for 22% of total inputs of nitrogen in the river networks. These results indicate that microbial processes of removal in sediments can eliminate significant parts of NH4+ generated from microbial pathways and/or inputs from anthropogenic activities in urban rivers. Overall, these results improve understanding of NH4+ production and removal and associated influencing environmental factors and highlight the environmental importance of these processes in regulating the NH4+ budget in highly urbanized riverine ecosystems.

No abstract

No abstract

Dissimilatory nitrate/nitrite reduction processes play an important role in controlling nitrogen loading in river environments. However, the relative importance of climatic temperature regime and biogeochemical controls to dissimilatory nitrate/nitrite reduction processes remains unclear. We used nitrogen isotope tracer approach to investigate geographical variabilities of denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) in river sediments from temperate to tropical climates of China. Denitrification, anammox, and DNRA varied greatly across the climatic gradient, with potential rates of 1.47–25.7, 0.54–3.4, and 0.15–7.17 nmol N g−1 h−1, respectively. Mean measured rates throughout the sampling sites were 9.73 nmol N g−1 h−1 for denitrification, 1.29 nmol N g−1 h−1 for anammox, and 1.61 nmol N g−1 h−1 for DNRA. Denitrification and DNRA rates increased significantly from temperate to tropical climates, while no significantly spatial difference was observed for anammox rates along the climatic gradient. Mean annual temperature, total organic carbon, dissolved organic carbon, pH, NH4+, NO3–, C/N, Fe2+, and functional genes were the crucial factors affecting denitrification, anammox, and DNRA. High dissolved organic carbon and NO3– availability determined nitrogen removal capacity in river sediments. Mean annual temperature was the most important factor explaining the geographical variances of denitrification and DNRA, while the critical predictor of anammox variance was sediment pH along the climatic gradient. Our results highlight that biogeochemical controls and climatic temperature regime are important coregulators affecting the geographical variabilities of dissimilatory nitrate/nitrite reduction processes in river sediments at the continental‐scale variation.