ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Marine Ecosystem Ecology
Volume 12 - 2025 | doi: 10.3389/fmars.2025.1684073
This article is part of the Research TopicAquatic Environment Changes of Vegetated Regions in Rivers, Marshes, and Coastal RegionsView all 6 articles
Characteristic and source quantification of nitrogen in sediments of a subtropical mangrove estuary
Provisionally accepted
- 1Zhejiang Guangchuan Consulting Co., Ltd., Hangzhou, China
- 2Sun Yat-sen University, Guangzhou, China
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The Qingjiang Estuary mangrove forest, located at the northernmost edge of China's mangrove belt, plays a vital role in maintaining regional ecological balance. This study investigated the sources and seasonal dynamics of nitrogen and organic matter across different vegetation zones within the estuary. Sediment samples were collected during both summer (June) and autumn (November), and analyzed for total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3⁻-N), total organic carbon (TOC), and C/N ratios. Stable isotopes (δ13C and δ15N) were used to quantitatively trace nitrogen sources. Spatially, nitrogen and carbon concentrations decreased from west to east across the estuary. The results revealed distinct seasonal differences in nitrogen forms and concentrations. TN and NO3⁻- N levels significantly increased in autumn, while NH4+-N remained relatively stable. Seasonal shifts in sedimentary environments strongly influenced nitrogen accumulation patterns. PCA results revealed that variations in sediment physicochemical properties in summer and autumn significantly influenced nitrogen distribution patterns. The first principal component (PC1, explaining 37.6% of variance) was dominated by TN, NO₃⁻-N, and water content, while the second component (PC2, explaining 18% of variance) was primarily associated with TOC, C/N ratios, and pH. Bayesian mixing model analysis indicated that organic matter primarily originated from terrestrial sources, including C3 and C4 plants, with minor contributions from aquaculture and marine plankton. The average contribution rates were: other terrestrial sources (24.6%) > C3 plants (23.83%) > C4 plants (23.75%) > aquaculture (16.7%) > plankton and marine sources (11.12%). These findings will provide important insights into nitrogen dynamics and source identification in the mangrove ecosystems.
Keywords: Qingjiang Estuary, Mangrove sediments, Nitrogen dynamics, Source analysis, Stable isotopes
Received: 12 Aug 2025; Accepted: 13 Oct 2025.
Copyright: © 2025 Qiu, Tan, Zhong, Sun, Luo and Niu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Lixia Niu, niulixia@mail.sysu.edu.cn
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