Phosphorus adsorption/desorption processes in the tropical Saigon River estuary (Southern Vietnam) impacted by a megacity

2019

Article référencé dans le Web of Science WOS:000489190500019

Nguyen T. T. N., Nemery J., Gratiot Nicolas, Garnier J., Strady Emilie, Tran V. Q., Nguyen A. T., Nguyen T. N. T., Golliet Claire, Aime Joanne

Estuarine Coastal and Shelf Science, 2019, 227, p. art. 106321 [13 p.] ISSN 0272-7714

The Saigon River flows through one of the most rapidly growing megacities of Southeast Asia, Ho Chi Minh City (HCMC, > 8.4 million inhabitants). This tidal river is characterized by a tropical monsoon climate, alternating a wet and a dry season. In the last few decades, increased economic and urban developments of HCMC have led to harmful impacts on the water quality of this tidal river, with severe eutrophication events. This situation results from the conjunction of contrasting hydrological seasons and the lack of upgraded sanitation infrastructures: indeed, less than 10% of the domestic wastewater is collected and treated before being discharged directly into urban canals or rivers. This study focuses on P dynamics because this is considered the key nutrient factor controlling freshwater eutrophication. Based on field measurements and original laboratory experiments, we assessed the P levels in the river water and sediments, and investigated P adsorption/desorption capacity onto suspended sediment (SS) within the salinity gradient observed. Field surveys showed a clear impact of the HCMC megacity on the total P content in SS, which increased threefold at HCMC Center, as compared with the upstream values (0.3-0.8 gP kg(-1)). Downstream, in the mixed estuarine area, the Total P was lower than 0.5 gP kg(-1). Laboratory experiments were carried out to characterize the influence of SS concentrations (SS = [0.25-0.9] g L-1 ), salinity (S = [2.6-9.3]) and turbulence (G = [22-44] s(-1)) on the sorption capacity of P onto sediment. The size of sediment particles and their propensity to flocculate were also originally measured with a recently developed instrument: the System for the Characterization of Aggregates and Flocs (SCAF (R)). Under the experimental conditions considered, SS concentrations had the greatest effect on the adsorption of P onto sediment, e.g., P adsorption capacity increased when SS concentrations rose. In contrast, salinity and turbulence had a smaller effect on the adsorption properties of sediments. Among these observed variables, the SS concentration was shown to be the main driver for adsorption capacity of P onto SS within the salinity gradient. We discuss the implication of these findings on understanding P dynamics within a highly urbanized, tropical estuary.

Limnologie physique / Océanographie physique [032] ; Ecologie, systèmes aquatiques [036] ; Hydrologie [062]

VIET NAM ; SAIGON COURS D'EAU ; ZONE TROPICALE

Fonds IRD [F B010077100]

fdi:010077100