Lai, Longyun, Müller, Moritz, Sukri, Rahayu Sukmaria, Wong, Changi, Mujahid, Aazani, Liu, Sumei, Xu, Zhaomeng, Rixen, Tim ORCID: https://orcid.org/0000-0001-8376-891X, Warneke, Thorsten, Notholt, Justus and Jiang, Shan (2025) Dissolved nitrogen in a tropical river-sea continuum: a seasonal view on the distribution and transformation. Deep Sea Research Part II: Topical Studies in Oceanography, 225 . p. 105583. DOI https://doi.org/10.1016/j.dsr2.2025.105583.

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Abstract

The Belait River is a typical blackwater river in Brunei, characterized by deep tea-brown water rich in dissolved organic matter (DOM) derived from surrounding peat swamps and rainforests. This study provides a systematic assessment of the chemical composition, transformation, and transport processes of dissolved nitrogen (N) in the Belait River during alternating wet and dry seasons by integrating nitrate (NO3−) stable isotope techniques with microbial analyses. Results indicate that dissolved organic nitrogen (DON) constitutes the primary component of total dissolved nitrogen (TDN), with its seasonal dynamics significantly controlled by hydrological climate and microbial activity. Along the salinity gradient, DON decreases due to dilution and degradation, while ammonium (NH4+) and NO3− accumulate significantly in densely populated areas owing to anthropogenic inputs. The extremely low dissolved inorganic phosphorus (DIP) concentrations in the Belait River highlight the crucial role of P limitation in maintaining the system's oligotrophic state. Through the investigation in this representative blackwater system, this study highlights complex N cycling mechanisms in blackwater and provides a critical gauge in land-ocean material fluxes at the Indo-Pacific Convergence Area.

Document Type:	Article
Programme Area:	PA2
Research affiliation:	Biogeochemistry and Geology > Carbon and Nutrient Cycling
Refereed:	Yes
Open Access Journal?:	No
DOI:	https://doi.org/10.1016/j.dsr2.2025.105583
ISSN:	0967-0645
Date Deposited:	09 Jan 2026 13:32
Last Modified:	09 Jan 2026 13:32
URI:	https://cris.leibniz-zmt.de/id/eprint/6063

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