Data/hora: 07/06/2024 11:07:05

Provedor de dados: | 5
País: | France

Título:

Dynamique des matières en suspension en mer cotière : caractérisation, quantification et interactions sédiments/matière organique

Dynamics of suspended particulate matter in coastal waters: characterization, quantification and interactions sediments / organic matter

Autores: | Chapalain, Marion.
Data: | 2019-01-28
Ano: | 2019
Palavras-chave: | Matière en suspension (MES); Floculation; Matière organique; Distribution en classe de taille; Dimension fractale; Capteurs optiques et acoustiques; Baie de Seine; Suspended particulate matter (SPM); Flocculation; Organic matter; Particle size distribution; Fractal dimension; Optical and acoustic sensors; Seine Bay.
Resumo: | The knowledge of suspended particulate matter (SPM) and turbidity dynamics in coastal waters is essential for studying marine ecosystems. Flocculation/deflocculation processes are crucial mechanisms controlling the dynamics of SPM physical characteristics and thus, the fate of these SPM in the environment. This PhD thesis focuses on the SPM characteristics and their dynamics in coastal waters, from tidal to annual scales, in response to hydrodynamic, hydrological and biological forcing that take place at the interface between estuaries and coastal seas. To this end, optical and acoustic sensors were deployed in situ through 6 field campaigns in 2016, in order to characterize and quantify SPM in the water column, near the mouth of the Seine estuary (France). A critical analysis of LISST-100X measurements in coastal waters is presented. The quantification of uncertainties on SPM concentration measurements is investigated: it highlights the crucial effect of salt retention, and the need for a minimum mass to filter, around 10 mg. A method for estimating an optimal filtration volume based on a reference turbidity measurement is proposed. High frequency measurements show that the dynamics of SPM and median diameter are controlled by the advection-flocculationsedimentation- resuspension cycle. These results allow to classify the factors controlling flocculation processes. Turbulence is identified as the main factor at the semi-diurnal and semi-lunar tidal scales, as the maximum median size of flocs decreases when the tidal currents intensify. At the seasonal scale, the variation of SPM characteristics (size, density, settling velocity) is correlated to the variability of the organic matter (OM) content: in particular, flocculation is enhanced by an increase of the particular OM fraction. The resulting larger and lesser dense flocs are also more resistant to the fragmentation induced by shear. This work also investigates the fractal approach applied to flocs. The fractal dimension variability, calculated by combining in situ data of SPM concentration and particle size distribution, can be associated to variations of the SPM composition, but can also result from uncertainties linked to instrument limitations. The latter are discussed in this PhD thesis. The seasonal variability of SPM characteristics is more pronounced offshore than at the mouth of the Seine estuary. From short-term observations in the Seine Bay and from long-term series in the Belgian coastal zone provided by the RBINS, optical turbidity and acoustic backscatter measurements are combined. They highlight an increase of the acoustic backscatter intensity when mean floc density decreases.
Tipo: | Text
Idioma: | Francês

Identificador:

https://archimer.ifremer.fr/doc/00500/61155/64591.pdf

https://archimer.ifremer.fr/doc/00500/61155/

Editor: | Université de Bretagne Occidentale
Formato: | application/pdf

Fonte:

info:eu-repo/semantics/openAccess

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