Biogeochemical controls on nitrogen transformations in subtropical estuarine wetlands

Nitrogen cycling in aquatic environments of China: Progress and future challenges

“…Mean annual temperature was observed to be the most important factor shaping the geographical distribution in the DNRA process. It has also been reported that DNRA rates (0.2-1.5 nmol g À1 h À1 ) varied spatially across the estuaries and coasts of China, but there were no obvious geographical distribution patterns (Yin et al, 2014;Li et al, 2020a). In most zones, the DNRA process was of minor importance in total NO 3 À reduction.…”

“…Summer N mineralization rates in the Yangtze Estuary were in a range of 1.5–85.4 μmol N g −1 d −1 , but winter rates decreased to 0.6–52 μmol N g −1 d −1 , and higher values generally occurred in muddy zones where C and N substrates are relatively abundant (Lin et al, 2016). In the Min River Estuary, potential N mineralization rates varied between 14.6 and 312.8 μmol N g −1 d −1 , which exhibited strong relationships to sediment moisture, C and N availability as well as urease activity (Li et al, 2020a). It has also been reported that N mineralization in benthic sediments of the Pearl River Estuary ranged from 0 to 48 μmol N g −1 d −1 , which were largely affected by sediment size, organic matter, nutrients, and Fe 2+ /Fe 3+ ratios (Huang et al, 2021).…”

“…All heterotrophic and chemoautotrophic microbes take up N to build biomass, just as photosynthetic organisms require N for assimilatory purposes (Damashek and Francis, 2018). Previous studies documented that sediment NH 4 + immobilization rates in the Yangtze Estuary, Min River Estuary, and Pearl River Estuary varied from 2.8–137 μmol N g −1 d −1 , 26.8–83.7 μmol N g −1 d −1 , and 0.3–36 μmol N g −1 d −1 , respectively, showing a large variation across estuarine and coastal ecosystems of China (Huang et al, 2021; Lin et al, 2016; Li et al, 2020a). These changes are mainly related to regional differences in temperature and C and N availability and are complicated by sediment grain size and moisture.…”

“…Temperature is generally considered as an important factor in regulating the physiological activity of microorganisms, and increased temperature can promote the NH 4 + immobilization rates (Lin et al, 2016). The C and N availability can provide energy and materials for microbial metabolisms and thus influence the NH 4 + immobilization process (Lin et al, 2016; Li et al, 2020a). Besides, significantly high sediment NH 4 + immobilization rates were also observed in urban rivers, with potential rates varying between 3.36 and 368 μmol N g −1 d −1 (Lin et al, 2017).…”

“…China is rich in diverse aquatic environments mainly including rivers, paddy fields, lakes, reservoirs, aquaculture ponds, estuaries and coasts, and constructed wetlands (Ma et al, 2021), which play important roles in global biogeochemical cycling. In the past few decades, N cycling processes and related N 2 O dynamics in aquatic environments of China have been increasingly documented due to improved analytical methods (Yin et al, 2014; Li et al, 2020a). In addition, the development of molecular techniques also has been well used to reveal microbiological mechanisms associated with N cycling dynamics in aquatic environments of China (Zhu et al, 2013; Zheng et al, 2014).…”