Recent agricultural occupation and environmental regeneration of salt marshes in Northern Spain

Abstract

Salt marshes reduce wave energy and offer natural protection from storms and floods. In the last centuries these coastal areas have been intensely impacted by human activities worldwide. In northern Spain, more than 50% of the original salt marshes have been reclaimed with agricultural purposes since the 17th century. However, many of these coastal wetlands have been recovered since the agricultural decline during the 1950s. Benthic foraminifera and sand content can be used as proxies to identify past episodes of salt-marsh reclamation and to analyze the environmental regeneration process of previously occupied lands. Foraminifera are absent in agricultural soils and increase in abundance during the regeneration of the area, until total recovery is reached. Similarly, sand content increases as tidal inundation takes place during the environmental regeneration period. The physical disturbance originated by reclamation presents a challenge for the 210Pb dating method. Nevertheless, historical aerial photography provides a good record for age estimation. This can be supported by chronostratigraphic horizons of major pollution events and nuclear weapon testing (i.e. heavy metals and 137Cs). In the current context of sea-level rise, sediment supply constrains the environmental regeneration of salt marshes. In northern Spain, abundant regional sediment input is available, allowing high sedimentation rates to happen during the regeneration process and facilitating adaptation to ongoing sea-level rise. Therefore, restoration of currently reclaimed tidal wetlands in global temperate coastal areas, with abundant sediment supply, can be considered as a soft adaptation measure against climate change consequences in the coastal zone.