These two processes play a pivotal role in the removal of excess nitrogen from ecosystems. This research sheds light on the multi-dimensional spatial patterns of denitrification and anammox along a 3,500 km latitudinal gradient, providing important insights into their contributions to global nitrogen cycling and offering implications for improving environmental management and biogeochemical models in river ecosystems.
Human activities such as agriculture, fossil fuel combustion, and nitrogen-fixing crop cultivation have led to a substantial increase in reactive nitrogen (N) inputs, reaching an estimated 210 Tg per year globally. Approximately 65 Tg of this nitrogen enters freshwater systems annually, contributing to environmental problems like hypoxia, algal blooms, and biodiversity loss. Denitrification, which converts nitrate (NO3−) to nitrogen gas (N2), has long been the main process for nitrogen removal in aquatic ecosystems. Anammox, discovered in the 1990s, is now recognized as a key process in nitrogen removal in freshwater and marine environments. However, the detailed spatial dynamics of these processes in natural river ecosystems have not been well understood, particularly across latitudinal gradients.
A study (DOI: 10.48130/nc-0025-0004) published in Nitrogen Cycling on 17 September 2025 by Wenzhi Liu’s team, Wuhan Botanical Garden, Chinese Academy of Sciences, highlights the importance of both denitrification and anammox in nitrogen cycling and offers new insights into the environmental and biological factors that regulate these processes in river ecosystems.
A research team conducted an extensive study to examine the environmental factors and biological communities influencing nitrogen removal processes in riverine ecosystems. The team measured total nitrogen (TN), ammonium (NH4+-N), nitrate (NO3–-N), and organic carbon concentrations in river water and sediment samples across different sites in China. The results showed that TN concentrations in river water varied from 1.4 to 10.6 mg·L−1, with NH4+-N and NO3–-N levels averaging 0.4 and 2.0 mg·L−1, respectively. Channel sediments and riparian rhizosphere soils contained the highest levels of NH4+-N and NO3–-N, respectively, while no significant differences were found across different soil types. Soil physicochemical properties, including total carbon (TC) and soil organic carbon (SOC) concentrations, were significantly higher in channel sediments and riparian rhizosphere soils than in riparian bulk soils. In microbial community analysis, denitrifying bacteria exhibited much higher abundance than anammox bacteria, with nirS gene abundance being greater in channel sediments and nirK gene abundance in riparian rhizosphere soils. Denitrification rates ranged widely from 0.4 to 195.5 nmol N g−1·h−1, with surface soils exhibiting the highest rates and both denitrification and anammox rates declining with soil depth. In channel sediments and riparian rhizosphere soils, denitrification was the dominant process, while anammox contributed more significantly in riparian bulk soils, accounting for 52.5%-58.3% of nitrogen removal. Statistical analysis revealed that soil physicochemical properties, such as SOC, iron content, and the abundance of nirS genes, were key factors influencing denitrification rates. For anammox, soil nitrate levels had the most significant impact.
Understanding the relative contributions of denitrification and anammox to nitrogen cycling in riverine wetlands can improve predictions of nitrogen dynamics, especially in regions where high nitrate concentrations lead to water quality issues. Integrating the anammox process into global nitrogen cycling models could lead to more accurate assessments of nitrogen removal potential and better strategies for managing aquatic ecosystems. Moreover, the research emphasizes the importance of riparian zones in nitrogen removal, particularly in areas with sandy, low-organic-matter soils. This highlights the need to preserve and restore riparian ecosystems to enhance their role in mitigating nitrogen pollution.
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References
DOI
10.48130/nc-0025-0004
Original Source URL
https://doi.org/10.48130/nc-0025-0004
Funding information
This work was supported by the National Natural Science Foundation of China (U24A20641, 32301369, and 32401364), the China Postdoctoral Science Foundation (2024M751752), and the Hubei Province Postdoctoral Science Foundation (2024HBBHCXB052).
About Nitrogen Cycling
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.