Possible impact of environmental policies in the recovery of a Ramsar wetland from trace metal contamination.

The Umia-Grove Intertidal Complex is located within the Ria of Arousa (NW Iberian Peninsula). Out of its significance for wintering shorebirds it has been included in the Ramsar List of Wetlands of International Importance as well as in international protection networks such as the European Natura 2000 and Important Bird and Biodiversity Areas-BirdLife International. In a sediment analysis conducted in the year 1999, the wetland was found to have been contaminated by potentially toxic trace metals, to wit: Cr, Cu, Ni, and Pb. Sediment samples retrieved in 2014 to make an updated assessment of the condition of the ecosystem showed evidence of the presence of selected trace elements, namely, Cd, Co, Cr, Cu, Ni, Pb, and Zn, within or slightly above the background ranges of local, regional, and general references. In the 15-year time frame between the two samplings there has been noticeable change in the relationship between nature and society as a consequence of the entry into force of a number of regulations aimed at avoiding the emission of contaminants; among others, the ban of Pb in gasoline, the deployment of wastewater treatment plants according to the European Water Framework Directive, and the limitation of the use of Cu pesticides. With the ensuing drop of human pressure, the self-purifying capacity of the ecosystem has effectively contributed to the wetland's recovery. Nevertheless, the application of a normalized enrichment factor to the more recent set of samples suggests the presence of relict low contamination by Cd, Cu, and Ni in localized areas. The compared analysis of the wetland condition in the two years is a sign of the success of the policies and regulations for environmental protection, but further work and more effectiveness are necessary in order to preserve threatened ecosystems of such importance as the Umia-Grove wetland.