The Arcachon Bay is a unique and ecologically important meso-tidal lagoon on the Atlantic coast of south-west France. The Arcachon Bay has the largest area of dwarf seagrass (Z. noltei) in Europe, the extent of which was stable in their extent between the 1950s and 1990s, but a decline in seagrass was observed in mid-2000. The decline of Zostera (seagrass) may have a significant impact on sedimentation in this coastal ecosystem rich in marine life. Interface cores were collected in September 2022 to determine sediment and mass accumulation rates (SAR, MAR) in the Arcachon Bay. Ten study areas were selected, distributed over most of the areas where seagrass meadows are actually observed. Two sites were visited each time, one with the presence of Zostera noltei in good condition (Healthy) and the other where the sediment was bare (Bare). Maximum water heights during spring tides range from 3.44 m for the deepest site (Garrèche) to 2.09 m for the shallowest site (Fontaines). A total of 20 sediment cores were sampled and carefully extruded every 1 cm from the top to the bottom of the core. The sediment layers were used to determine dry bulk density and selected radioisotope activities: DBD, 210Pb, 226Ra, 137Cs, 228Th and 40K expressed as %K). 

The ReZoEnv field campaign was conducted at 9 sites distributed within contrasted seagrass (Zostera notlei) meadows in the Arcachon Bay. This multi-parameter survey was conducted during one year (November 2015 – November 2016). Water levels, temperature and light were recorded every 10 minutes. While bed sediment characteristics (granulometry, water content, organic matter content), seagrass characteristics (coverage, biometry, chlorophyll and CNP content) were measured monthly. Additionally, wind-wave parameters were obtained from high frequency pressure sensor at 4 sites, every 20 minutes. List of sites : - ANDE : 44.745091 N, 1.121366 O - FONT : 44.722631 N, 1.080133 O - GAIL : 44.662573 N, 1.099575 O - GARR : 44.705132 N, 1.121562 O - HAUT : 44.729331 N, 1.15608 O - ILE : 44.683117 N, 1.162716 O - JACQ : 44.724563 N, 1.181109 O - PASS : 44.689927 N, 1.089491 O - ROCH : 44.648529 N, 1.127736 O