Project summary:
The DYSTRO-B project explores the effects of eutrophication and dystrophy on the structure and productivity of phytoplankton communities in the Bay of Seine. These phenomena, linked to the excess of nutrients such as nitrogen (N) and phosphorus (P) from human activities, disturb the ecological balance of coastal zones. The project examines how these imbalances, amplified by the warming of the waters, influence the diversity, the size, the composition and the productivity of the phytoplankton communities.
Background:
The Bay of Seine is particularly vulnerable to eutrophication due to the massive supply of nutrients via the Seine. Although measures have made it possible to reduce phosphorus intakes, nitrogen remains present in high quantities, causing an imbalance (N/P ratio ≈ 30, well above the ideal Redfield ratio, N/P = 16). These imbalances have repercussions on phytoplankton biomass, community structure and essential ecosystem services.
Objectives:
The project aims to:
- Analyze the evolution of phytoplankton communities in the face of nutrient imbalances (dystrophy) and warming waters.
- Evaluate the impacts on primary productivity and the associated carbon fluxes.
- Develop multiscale approaches to better understand the interactions between nutrients, specific diversity, and ecosystem functioning.
Methodology:
project is structured around three axes:
- Retrospective analysis: Study of data collected over the long term (SOMLIT, PHYTOBS, RHLN, REPHY networks) and high frequency (SMILE buoy) to understand trends and one-off events related to the dynamics of phytoplankton communities
- Experiments in microcosms: Study of natural communities sampled in the Bay of Seine to test the effect of N/P ratios on productivity and community structure.
- Phytoplankton cultures: Laboratory studies on monocultures of taxa characteristic of the bay in order to better understand the physiological mechanisms and acclimatizations linked to the variation of N/P ratios.
Expected results:
The project will provide a better understanding of the processes linking nutrient availability, diversity and phytoplankton productivity to contribute to the construction of scenarios on the trajectory of this highly anthropized ecosystem.
Lise Delatte‘s thesis is carried out as part of this project.
