THE SEDIMENTARY RECORD OF AGRICULTURAL ACTIVITIES IN COASTAL MARSHES AND THEIR NATURAL REGENERATION: EXAMPLES FROM THE SOUTHERN BAY OF BISCAY

Understanding the dynamics of salt marshes is key under the current climatic scenario. With this objective we took 50-cm long sediment cores from recently regenerated salt marshes in the southern Bay of Biscay. These cores were analyzed using microfaunal and geochemical proxies and the results were integrated with historical data. Agricultural soils, previously isolated from tides, were abandoned during the 1950s resulting in the entrance of estuarine waters thought tidal flooding, similar to the possible effect of extreme sea-level acceleration. However, instead of the expected drowning of these anthropogenic areas they experience a rapid natural environmental transformation. Increasing amounts of sand and benthic foraminifera were deposited at a very high sedimentation rate (average 16 mm yr-1) during the 1950s and 1960s allowing rapidly recolonization of these formerly occupied areas. During recent decades much lower sedimentation rates (average 2.5 mm yr-1), abundant agglutinated foraminiferal assemblages and enrichment of Pb and Zn due to industrialization are characteristic of these already regenerated environments. This rapid regeneration process is of great interest for environmental management of coastal areas, where extensive reclaimed land could be easily restored to tidal wetlands under the current accelerating sea-level rise.