OSUG - Terre Univers Environnement


Biogéochimie et contaminants / soutenance en 2018

18 janvier 2017 ( maj : 18 mai 2018 )

Risque d’eutrophisation dans la rivière Saigon : impacts des rejets de la métropole d’Ho Chi Minh Ville sur la zone côtière

directeurs de thèse : Julien Némery - Nicolas Gratiot - Phong T. Nguyen


The Vietnamese authorities are increasingly concerned about the rising risk of deterioration of water resources affecting aquatic and continental coastlines. Although upstream river water quality is good, the downstream basin of major rivers expose poor water quality and most of the lakes and canals in municipal areas are fast becoming sewage sinks. The effects of natural and human activities on water resource are the matter with a strong tendency not only in local (Vietnam) but also in global. And anthropogenic activities have significantly altered nitrogen (N), phosphorous (P), carbon (C) and silica (Si). The nutrient input into the drainage network of N, P, and Si from diffuse and point sources are very different from each other as are in-stream processes affecting their transfers. Their concentration and flux at a different place of rivers can vary significantly in response to short-term variations in hydrology and long-term changes of land use and population. These changes may result in changes of nutrient limitation patterns, leading to basic alternations of ecosystem structures and functions. The content of nutrients (N, P, Si) carried to the coastal zone by large river systems, as well as the balance between these elements, are the major determinants of coastal marine eutrophication problems. These excess nutrients and changes in C/N/P/Si lead to massive development of algae, deoxygenating of the water column and can favor the development of toxic algae (cyanobacteria). One issue is to identify the origins of this nutrient pollution and the phases on which the elements are transported in aquatic environments. Furthermore, sediments conveyed by rivers to coastal zone have played an essential role in the biogeochemical phases of many elements, particularly nutrients elements such as N, P, C and Si. We distinguish point sources contributions under dissolved form (domestic and industrial wastewaters) and particulate diffuse inputs strongly linked to the dynamics of sediment from soil erosion. And many types of research have been carried out on the water quality of rivers water support systems in over the world. However, few of scientific have concerned water quality in the river for the whole river system, especially in Vietnam in general and in HCMC in particular. With aforementioned gap, this study has conducted to survey the concentration of nutrients to explore the status and driving factors of water quality of Saigon River and Can Gio Mangrove.

Objectives of this study

The overall objective of this thesis is to outline the water quality status of Saigon River and to provide the scientific understanding of natural and anthropogenic factors affecting Saigon River water quality. And the specific objectives are :

Preparing a complete database of water discharge and then use this information to elucidate the complex water circulation and calculate synthetic spatial water budget.Determination concentration of nutrients that is rejected by HCMC to Saigon River.Quantifying the different form (dissolved or particulate inorganic and organic nutrients) and ratio of C:N:P:Si in downstream (Can Gio Mangrove) to assess trophic state and risk of eutrophication for Can Gio Mangrove.Studying exchangeable nutrients from sediments to a water body and assessing nutrient behaviours in suspended sediments and salinity gradient in order to evaluate these retention capacities with respect to the nutrient fluxes delivered from the upstream watershed.