Title: A systematic review of tracing nitrogen cycle and source in freshwater ecosystems

Authors: Indahayu Ab Rahman; Amir Shah Ruddin Md Sah; Syahidah Akmal Muhammad; Munirah Abdul Zali; Fu-Jun Yue; Si-Liang Li; Widad Fadhullah

Addresses: Environmental Technology, School of Industrial Technology, Universiti Sains Malaysia, USM 11800, Pulau Pinang, Malaysia ' School of Biological Sciences, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia ' Environmental Technology, School of Industrial Technology, Universiti Sains Malaysia, USM 11800, Pulau Pinang, Malaysia; Analytical Biochemistry Research Centre, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia ' Analytical Chemistry Applications Group, Waste Technology and Environment Division, Malaysian Nuclear Agency, 43000, Kajang, Selangor, Malaysia ' Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China ' Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China ' Environmental Technology, School of Industrial Technology, Universiti Sains Malaysia, USM 11800, Pulau Pinang, Malaysia

Abstract: Nitrogen pollution in freshwater ecosystems is a growing concern due to human activities like agriculture, urbanisation, and industrial discharges, which disrupt the nitrogen cycle and pose ecological and public health risks. This review synthesises recent advancements in identifying nitrogen sources and transformations in freshwater ecosystems, emphasising methodologies, findings, and management implications. A comprehensive literature search was conducted using databases such as Scopus, Web of Science (WoS), and ScienceDirect, focusing on studies from 2021-2024. Following the PRISMA framework, 50 primary studies were analysed. The findings are categorised into four themes: 1) nitrogen source identification; 2) nitrogen transformation and cycling; 3) isotope tracing and modelling; 4) external factors affecting the nitrogen cycle. The study highlights the importance of integrating traditional and advanced methods to tackle nitrogen pollution. It concludes that region-specific research and improved tracing techniques are essential for sustainable freshwater management and ecosystem resilience.

Keywords: nitrogen cycle; nitrogen source; nitrogen transformation; freshwater; ecosystems; bacterial denitrification; stable isotopes; modelling.

DOI: 10.1504/IJEWM.2026.154486

International Journal of Environment and Waste Management, 2026 Vol.40 No.2, pp.166 - 199

Received: 11 Feb 2025
Accepted: 18 May 2025
Published online: 30 Jun 2026 *

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