LandSeaLot Integration Labs: Spotlight on the Seine Estuary and Bay
What is an Integration Lab?
LandSeaLot Integration Labs are testing sites for developing a common strategy for observing land-sea interface areas across Europe. They are piloting new methods, technologies and community-based approaches to improve observations and understandings of essential areas like river mouths, estuaries and deltas. These observations provide key knowledge to scientific and stakeholder communities, enabling them to tackle important societal challenges.
Exploring the Seine Estuary and Bay
• The Seine River in Northern France is surrounded by a large basin of around 76,000km². Home to 17 million people, the basin encompasses the Paris metropolitan area and drives industrial and agricultural activities. It is connected to the English Channel through the Seine Estuary, a 170 km-long meandering estuary that supports key habitats and important biodiversity and ecological functions.
• As an interface between marine and freshwater ecosystems, the Seine Estuary is a mosaic of subtidal areas, intertidal mudflats, salt marshes, ponds, wet meadows and reedbeds.
• The area also hosts essential ecosystem services, such as the significant ports of Le Havre and Rouen. The Seine’s watershed accounts for 50% of river traffic in France, 40% of the country’s economic activity, and 30% of agricultural activities.
Pressures on the Area
Human-induced transformation of the estuary
• Over the past 200 years, the Seine Estuary has undergone extensive human-led changes to support port industries and maritime traffic. These changes have significantly altered the estuarine ecosystem, reshaping its morphology through river channelisation, port extension, and polder creation and converting wetlands into croplands. Between 1970 and 2020, the total surface area of the estuary decreased by 22%, mainly due to the loss of intertidal areas (approx 1,500 ha lost) and wetlands (approx 6,000 ha lost).
Impact of climate change on estuarine morphology and habitats
• The sediment fluxes and by extension the actual morphology of the Seine Estuary result schematically from the complex interaction between the tides and river flows that import sediments, the storms that export them, and human interventions such as maintenance and dredging. The intensification of extreme
events (e.g. river floods and storms), as well as sea level rise combined with tidal activity, are changing how much sediments are imported to or exported from the estuary. This combination impacts water quality, influences morphological change and affects the distribution of key subtidal and intertidal habitats.
Nutrient inputs
• Nutrient inputs to the Seine estuary primarily result from agricultural activities, urban and industrial discharges in the watershed. While phosphorus and ammonia flows have been significantly reduced through urban treatment efforts, nitrate flows remain high, partly due to the decrease in surfaces with high filtering capacity. The presence of these nutrients represents the basis for primary production in the estuary, which is the foundation of the food chain. In the Seine Bay, an excess or imbalance of these nutrient inputs could promote the growth of certain phytoplankton species that may produce toxins, posing health risks in the case of shellfish consumption.
Understanding and addressing challenges
Scaling up observations
• By combining in situ observations, satellite data and numerical models, the Seine Estuary and Bay LIL aims to improve observations of this land-sea interface area. Integrating these methods and data streams is a crucial step to filling knowledge gaps and addressing the impacts of climate change on hydrodynamics, sediment fluxes and seabed morphology in the Seine Estuary and Bay.
Modelling future scenarios
• Researchers are creating numerical models of water dynamics and sediment transport to predict future environmental changes under different climate scenarios, including sea level rise, and extreme weather or (distorted) river discharge regime. This knowledge is crucial to evaluate the future availability of essential habitats supporting biodiversity in the LSI, such as intertidal mudflats.
Biodiversity of essential organisms
• Researchers will investigate the impact of nutrient inputs and their impact on phytoplankton dynamics and biodiversity. Phytoplankton refers to microscopic organisms which drift through surface waters, sometimes changing the color of water. As a building block of the marine food chain and an essential producer of oxygen, phytoplankton is essential to the land-sea ecosystem and life on Earth.
Emerging methods and collaborations
• The Seine Estuary and Bay plans to deploy cost effective technology to observe parameters testing cost effective technology including water temperature, salinity and turbidity. This technology will first be tested onsite, before training and deployment with local communities.
• The LIL will collaborate with local stakeholders including port services, marinas at Le Havre and the Port of Calvados, professionals such as fishers, NGOs, water agencies and other government services. They will also work closely with PHENOMER 2.0, a program that recruits citizens to observe and report water color changes due to phytoplankton blooms.
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