Conservation approach of a front dune system through the study of its blowouts (Cala Agulla, Mallorca)

Abstract

[eng] Most of the beach-dune systems in the western Mediterranean today show an important state of fragmentation with obvious signs of erosion, largely because of blowouts on the dune front. Blowouts were studied in the dune front of the Cala Agulla beach-dune system (Mallorca, Spain) in order to better understand and quantify the backward dune movement over the last decades. A spatiotemporal analysis taking into account the boundary drawn by the vegetation along the first line of dunes was carried out. The analysis was performed using GIS software ArcView, applying DSAS extension 2.0 (Digital Shoreline Analysis System). Fourteen blowouts located along a front about 600 m long were studied. For each blowout, some ecological and morphometric variables were analyzed in order to establish the relationship between the different types of blowouts. To this end, it was applied an index Rt-v to link each morphology with the patterns shown by the existing vegetation, both herbaceous and woody. Applying the iTx index represents the link between each typology and its inner topography. The results show integral recoil of the dune front over the last decades - the average recoil ranges from 10-20 m, although in some places exceed 20 m -. However, from 2008 to 2010 some advances were recorded, except at the sites that coincided with the main entrances to the beach, which suggests a direct relationship between maximum erosion and the places with highest attendance. Blowouts were divided into 5 categories, trough blowouts being the most prevalent (50% of samples). Each type showed distinct morphometric features and had a different relationship with the vegetal species.