About

OVERVIEW

Plastic pollution is recognised as one of the most critical anthropogenic issues in aquatic environments worldwide. Microplastics (MPs, <5mm) are particularly problematic due to their abundance and their capacity to travel over long distances, threatening ecosystem structure, functions, services, and values.

At the land-ocean interface, estuaries are privileged pathways of MPs. Around three-quarters of plastic waste reported in the ocean are estimated to come from land-based sources, primarily via rivers and estuaries. However, not all plastic entering estuaries are flushed into the ocean. We can hypothesize that, as fine sediments and particulate organic matter, MPs may be trapped in estuaries forming regions of privileged accumulation. This trapping may be particularly significant in macrotidal estuaries characterized by significant landward residual fluxes of sediments. Therefore, macrotidal estuaries may be a major temporal or permanent sink of MPs.

However, this is not fully demonstrated. Compared to sediments, MPs cover a larger spectrum of physical properties (density, size and shape) that can vary over time due to weathering and biofouling processes. Very little is known about the physical mechanisms of transfer and trapping of MPs at the river-estuary-sea continuum. 

This is primarily because (1) of the limited contribution of coastal physicists to plastic pollution research compared to other disciplines; (2) sampling protocols are not adapted to all the representative timescales of variability in estuaries and are disassociated from the observation of physical variables; (3) sampling post-processing is time-consuming; (4) numerical studies of MPs transport mainly focused on ocean scales, ignoring vertical gradients and the physical processes of shallower environments.

GENERAL OBJECTIVE

PLASTINEST aims to make fundamental progress in understanding the transport, trapping and dispersion of MPs in estuaries dominated by tides using well-adapted and innovative field measurements, physical experiments, and improved numerical modelling.

PLASTINEST will provide fresh insight into the physical processes governing the transport of the different types of particles in relation to environmental forcings and their variability, ultimately contributing to quantifying the distribution and budget of MPs at the land-ocean interface. 

SPECIFIC OBJECTIVES

  1. To describe MP vertical dynamical, in particular MP settling dynamics in hyperturbid environments and MP erodability in cohesive sediment beds.
  2. To evaluate the spatio-temporal variability of microplastic pollution in connection with hydrodynamics.
  3. To understand key trapping processes such as estuarine fronts and Estuarine MPs Maxima (EMPM).
  4. To optimize and implement a numerical model to simulate the transport and trapping of MPs.
  5. To advance knowledge of MP transport at the estuary scale under changing environmental forcings.

STUDY CASE

The Gironde estuary (SW France) is an ideal natural laboratory to achieve this challenge. It is one of the largest European estuaries, a major contributor of suspended particulate matter to the Bay of Biscay, and is characterized by strong sediment trapping.

PLASTINEST will cover three regions from the river to the ocean – the tidal river, the main estuary and the near-field plume – and will primarily focus on tidal and seasonal time scales.

Know more about the Gironde estuary here.

DURATION

4 years (01/11/2022-30/10/2026)

COSTS OF THE PROJECT ACTION

285 150 € granted by the Young Research Program (JCJC) of the French National Research Agency (ANR).