Marion Drouzy (OPLC Team) will defend her thesis on Thursday, December 12 at 9am in the Oceanomed amphitheatre

On the following subject:
"Study of the natural and anthropogenic terrigenic impact on a tropical lagoon system using a 3D hydro-sedimentary modelling approach linked to a measurement network"
Thesis Director: Christel Pinazzo, Senior Lecturer
Co-director: Pascal Douillet, Research Officer

This cited PhD thesis takes place in New Caledonian economic and environmental delicate context. Caledonian coral reef is the second largest in size, and its lagoon shelters the biggest marine biodiversity of the Pacific Ocean. It so became inscribed to the UNESCO world heritage in year 2008. However New Caledonian Economy mostly depends on nickel open-pit mining and industry. Nickel extraction requires deforestation of large woodlands, leading to anthropogenic erosion of soils. These terrigenous particles inputs are driven to the creeks and rivers, ultimately discharging in the lagoon. This man-made increase of terrestrial inputs, transported in the lagoon as suspended particulate matter (SPM) can be a real stress for the marine ecosystem:
- While transported in the water column, the SPM can trigger shading over corals, causing death by lack of light for photosynthesis.
- When it sediments, SPM can smother corals and benthic life
- It can also pollute marine life if SPM are contaminated by heavy metal or chemicals during mining processes.
The PhD thesis takes place in New Caledonian economic and environmental delicate context. The main objective of this thesis is to develop and validate a hydrodynamic 3D model, taking into account physics and meteorological forcing, in order to simulate SPM transport, flocculation, deposition and resuspension. These processes have yet never been implemented in 3D modeling in New Caledonia. The ultimate goal is to predict the impact of mining activity in both short and long run. The modeled area includes two bays in the Southeast lagoon, one of which is under mining influence and the other is not impacted, so as to compare both evolution of SPM transport.
The development of such a model induced a first phase of data acquisition, which was realized during this last 1rst year of PhD, with the purpose of characterizing SPM flow rate, nature, and transport through hydrodynamic patterns in the bays of interest. The second year will be focused on the analysis of optical and physical measurements, particle size sorting and deposition processes, as well as the launching first simulations of dissolved and particulate matter.

Keywords : deposition,hydrodynamics,modeling,,