SELAMIK campaign: studying the causes and impact of hyper-sedimentation in the Voh-Koné lagoon, New Caledonia

Located at the interface between the continent and the ocean, the New Caledonian lagoon is particularly sensitive to anthropogenic pressures. In recent years, scientists have observed an increase in sedimentation in the lagoon bordering the industrial site of Vavouto. The oceanographic campaign SELAMIK, organized aboard the Alis from March 3 to 16, 2022, aims to understand the origin, fate and impact of sedimentation on the functioning of this lagoon.

In the South Pacific, New Caledonia is an archipelago surrounded by one of the largest lagoons in the world with a total area of 24,000 km2. The ecosystems of this lagoon are strongly impacted by the combined effects of climate change and human activities because their ecological balance is all the more fragile as the volume of lagoon water is low and their reef barrier restricts exchanges with the ocean. However, the lagoon plays a recognized role as a nursery for many species and provides many services to populations. It must therefore be preserved against the undesirable effects of a poorly controlled development. Deforestation and soil erosion modify the functioning of this ecosystem and limit the development of blue economies such as fishing, aquaculture and tourism. Among the other anthropic pressures facing the lagoon, the impact of extractive mining activity is major. Although it contributes significantly to the economic development of New Caledonia, such activity represents many risks for society and the environment, especially for the coastal environments.

During the UECOCOT oceanographic campaign that took place in the Voh-Koné lagoon in 2018, scientists observed an increase in sedimentation in this area, associated with a decrease in marine biodiversity. The massive sedimentation observed seems to have had undesirable effects such as the rarefaction (sea cucumbers) or disappearance (sea urchins, clams) of species that are abundant in neighboring lagoons. This observation (not documented until now) is at the origin of the SELAMIK project, whose objective is to understand the contribution of mining activities on the massive hyper-sedimentation of the Voh-Koné lagoon.

More concretely, the objective is to analyze the hydro-sedimentary processes in this lagoon in order to determine the causes of this hyper-sedimentation and to evaluate the consequences on the ecosystem functioning. For this, scientists will try to answer 3 questions:

1. What are the main hydrodynamic forcings in the lagoon?

2. What is the role of sediments in the regulation of the physico-chemical equilibrium of the lagoon?

3. What is the impact of particulate inputs on microbial communities?

Field operations will include the deployment of sensors to measure currents, the collection of sediment and suspended particle samples for the measurement of environmental parameters (carbon, nitrogen and organic phosphorus, chlorophyll), metallic elements and microbial diversity.

Contacts

IRD New Caledonia Communication Department:

Karla Bussone | karla.bussone@ird.fr | 26 08 04

Scientific manager of the SELAMIK campaign :

Cristèle Chevalier | cristele.chevalier@mio.osupytheas.fr | 06 87 28 26 14