Removal Capacities and Environmental Constrains of Denitrification and Anammox Processes in Eutrophic Riverine Sediments

Abstract

Excessive nitrogen (N) loading has had severe consequences in coastal zones around the world. Denitrification and anammox are major microbial pathways for removing N in aquatic environments before it is exported to the coast. To assess two processes in eutrophic riverine systems, the denitrification and anammox and their bacterial participants were investigated in sediments of the Xiaoqing (XQ) River and Jiaolai (JL) River in Northeast China. By combining the evidence from N 15 isotope tracing experiment and functional gene-based analysis, it was found that denitrification and anammox are ubiquitous along the investigated riverine sediments. The denitrification varied from 39.38 to 1433.01 nmol N 2 m −2 h −1 . Moreover, the anammox rates were in the range of 15.91 to 1209.97 nmol N 2 m −2 h −1 . Quantitative PCR results revealed that the nirK and nirS genes were in the order of 10 4 -10 6 copies g −1 and 10 3 -10 5 copies g −1 , respectively, in both river sediments, while the hzsA was in the order of 10 6 -10 5 copies g −1 in XQ at approximately two orders of magnitude compared with JL. The phylogenetic analysis of functional genes revealed the high diversity of the denitrifier and low diversity of anammox bacteria. Variance partitioning analyses verified that the grain particle characteristics were the major factor group determined the N removal efficiency. The denitrification and anammox processes were estimated to have removed 16.1% of the inorganic nitrogen inputs before being exported to Laizhou Bay, which highlights that a more extensive understanding of the regularity of the N removal processes is important in the technical remediation of eutrophication problems.

An Underestimated Contribution of Deltaic Denitrification in Reducing Nitrate Export to the Coastal Zone (Po River–Adriatic Sea, Northern Italy)

“…As the N availability in receiving water bodies increases, excessive algal growth is stimulated and the eventual organic matter results in bottom water anoxia and cascading effects such as biodiversity loss, and alterations in food web structure and function [1,2]. At the same time, riverine sediments are active sites for biogeochemical reactions, such as denitrification, which acts as a natural buffer against nitrate (NO 3 − ) pollution [3,4]. Denitrification, the stepwise reduction of NO 3 − to nitrogen gas (N 2 ) under anaerobic conditions, is widely recognized as the dominant biogeochemical process responsible for permanent N removal in rivers and transitional environments [5][6][7].…”

Nutrient Dynamics and Ecosystem Metabolism of Megacity Rivers: Influence of Elevated Nutrient Concentrations in Beijing’s Waterways

“…In urban rivers, N and P are regarded as major pollution stressors and reach urban waterways via multiple sources [9][10][11]. For example, vehicle exhaust and atmospheric deposition [12,13], urban impervious surface [14,15], and wastewater treatment plant (WWTP) effluents [16,17] all can contribute to elevated N or P in urban rivers. The impairment of water quality and ecological function caused by excessive nutrients in urban rivers is the core concept of the Urban Stream Syndrome (USS) which provides a framework for evaluating responses to urbanization [4,[18][19][20][21].…”

Nutrient Dynamics at the Sediment-Water Interface: Influence of Wastewater Effluents

“…Urban areas are the focus of nutrient pollution due to both point and non-point pathways to urban rivers (Wakida and Lerner 2005). For example, urban impervious areas are known to contribute to elevated nutrients in urban rivers (Bedore et al 2008;Dodds 2006;Li et al 2020). The loss of vegetation and soils that effectively entrap particulate nutrients can lead to higher loads than if the vegetation and soil were in place.…”