POSTER SESSION 3
15:30–17:30, Wednesday, September 16
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1237 | POSTER 227
PHYTOPLANKTON BIOMASS DYNAMICS AND EMERGING EUTROPHICATION RISK IN SOUTHERN VIETNAM’S ESTUARINE SYSTEMS: A DECADE OF SENTINEL-3/OLCI AND SENTINEL-2/MSI OBSERVATIONS
Despite undergoing rapid hydrological and anthropogenic changes, southern Vietnam’s estuarine systems remain poorly investigated for their long-term phytoplankton dynamics from remote sensing. This study used Sentinel-3/OLCI and Sentinel-2/MSI observations (2016-2025) to investigate Chl-a variability and eutrophication risk across these systems. Timeseries decomposition of OLCI data showed that Chl-a variability was dominated by the seasonal pattern, accounting for over 80% of total variance and confirming monsoon influence. In the inner estuarine channels, discharge was positively correlated with SPM but negatively with Chl-a, confirming that runoff governs phytoplankton biomass through turbidity and light availability rather than nutrient supply. In contrast, offshore waters exhibit positive correlations between discharge and both Chl-a and SPM, highlighting the fertilizing influence of river-plume export. A Productivity Constraint Boundary was established from the Chl-a/SPM relationship, yielding a threshold of ~31 mg.L–1 where turbidity becomes a light-limiting factor for phytoplankton development. Trend analysis showed the more pronounced increase in Chl-a at the Saigon–Dong Nai confluence compared to Mekong branches. OLCI observations detected a significant Chl-a increase of +3.80% year–1 with a concurrent SPM decline of -2.23% year–1. Sentinel-2 data revealed that although the Saigon River Estuary remained highly eutrophic, with local Chl-a exceeding 100 μg.L–1 in urban reaches, no clear temporal evolution was detected. The increase at the confluence appeared primarily driven by the Dong Nai tributary under declining SPM conditions. The urbanized Saigon tributary is particularly sensitive to discharge, with Chl-a increasing under low flow, as evidenced by the 2020 drought.
Manh Tran, University Littoral Côte d’Opale, CNRS, University Lille, IRD, and LOG – Laboratoire d’Océanologie et de Géosciences, France, [email protected], https://orcid.org/0000-0003-4770-5561
Truong An Nguyen, Université Grenoble Alpes, CNRS, IRD, INRAE, France, [email protected]
Julien Némery, Université Grenoble Alpes, CNRS, IRD, INRAE, France, [email protected]
Julien Masson, University Littoral Côte d’Opale, CNRS, University Lille, IRD, and LOG – Laboratoire d’Océanologie et de Géosciences, France, [email protected]
Gwenaël Abril, Marine Eutrophication Lab, MAREL, CNRS – UERJ – UFF, Brazil, [email protected]
Vincent Vantrepotte, University Littoral Côte d’Opale, CNRS, University Lille, and LOG – Laboratoire d’Océanologie et de Géosciences, France, [email protected]
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
