A macrotidal hyperturbid fluvial-estuarine system
With a total surface area of 635 km2, the Gironde is a macrotidal fluvial-estuarine system located on the Atlantic
coast (southwest France). The estuary shows a regular funnel shape of 75 km between the mouth and the junction of
the Garonne and the Dordogne rivers. At the Gironde mouth, tides are semidiurnal
and the mean neap and spring tidal ranges are respectively 2.5 and 5m (Jalón-Rojas et al., 2018). As the tide propagates upstream, tidal currents undergo an increasing flood-dominant asymmetry. The tidal asymmetry and the subsequent tidal pumping coupled with density residual circulation are the main mechanisms leading to landward transport and accumulating suspended sediments in a pronounced Estuary Turbidity Maximum (Jalón-Rojas et al. 2015). In surface waters, suspended sediment concentration can reach up to 10 g/L (Defontaine et al., 2023).
Ecologically, the estuary is a unique and biodiverse ecosystem, providing habitat for a variety of plant and animal species, including several commercially important fish species. The estuary also plays a crucial role in the nutrient cycling and carbon storage of the region. Economically, the Gironde estuary is a major shipping route, connecting the port of Bordeaux to the Atlantic Ocean and facilitating the transportation of goods and commodities such as wine, grain, and petroleum. The estuary also supports a thriving tourism industry, with visitors drawn to the region’s natural beauty, cultural heritage, and gastronomy.
Before PLASTINEST, no comprehensive research has been conducted to describe microplastic pollution in the Gironde Estuary. Nevertheless, de Carvalho et al. (2021) have estimated the levels of microplastics in surface water at 14 locations situated upstream of the Garonne tidal river, within the Garonne river basin. The study measured microplastic concentration, within a size range of 700 μm to 5mm, and found that it averaged 0.15 items · m−3, with a range between 0 to 3.4 items · m−3.