Ammonium Production and Removal in the Sediments of Shanghai River Networks: Spatiotemporal Variations, Controlling Factors, and Environmental Implications

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.

Dissimilatory Nitrate/Nitrite Reduction Processes in River Sediments Across Climatic Gradient: Influences of Biogeochemical Controls and Climatic Temperature Regime

“…It has been reported that anaerobic respiration can tend to more accumulation of sulfide in organic matter‐enriched environments (Giblin et al, ; Jensen et al, ). Therefore, the inverse relationships of anammox with DOC and NH 4 + in our study may be attributed to the higher sulfide inhibition on anammox in the high DOC and NH 4 + content environments (Jensen et al, ; Lin et al, ). The partial correlation analysis controlling for sediment pH indicated that mean annual temperature had no significant influence on anammox rates, which in turn reflected the dominant role of pH in regulating anammox rates throughout the rivers.…”

“…However, denitrification, anammox, and DNRA exhibit different sensibilities in response to temperature changes. Previous studies reported that there was no significant seasonal difference in anammox rates, although the high anammox rates were observed in winter (Lin et al, ; Lisa et al, ). Anammox was not detected even in tropical estuarine sediments (Dong et al, ), further suggesting a limited effect of temperature on anammox.…”

“…Denitrification and anammox can export nitrogen mainly through N 2 , N 2 O, and NO emissions (Reisinger et al, 2016;Stelzer et al, 2014;Stelzer & Bartsch, 2012;Xiong et al, 2017), while DNRA retains nitrogen as a more bioavailable ammonium for recycling in the rivers (Kim et al, 2016;Lin et al, 2017;Shelley et al, 2017). In many inland aquatic environments, denitrification is the dominant pathway of nitrate/nitrite reduction, which has been found to account for over 80% of total NO 3 − removal (Kreiling et al, 2011).…”

“…Unlike denitrification and anammox, DNRA is a heterotrophic process converting nitrate/nitrite into more bioavailable ammonium, which retains nitrogen for recycling within aquatic environments (Kim et al, 2016;Lin et al, 2017;Nogaro & Burgin, 2014;Shelley et al, 2017). It has been reported that DNRA can proceed using organic carbon for fermentative pathway or sulfide and Fe 2+ for chemoautotrophic metabolisms (Giblin et al, 2013).…”

Bacterial Community Shifts Driven by Nitrogen Pollution in River Sediments of a Highly Urbanized City

“…A previous study reported that NH 4 + has a positive effect on Actinobacteria abundance, and NO 3 − shows a positive correlation with Armatimonadetes , Chloroflexi and Bacteroidetes abundances [14]. In addition, nitrogen transformation pathways in urban rivers have been reported to alter in response to the increasing nitrogen input from anthropogenic activities [17,18], which may be attributed to the shifts of bacterial community [6,19]. Although these studies have improved our understanding of the alterations in microbial community composition and nitrogen cycling under nitrogen pollution stress, knowledge of the dynamics of bacterial diversity and abundance in river sediments impacted by large amount of nitrogen inputs is still limited in the highly urbanized areas.…”