Evolutionary stages of active to vegetated coastal transgressive dunefields in the San Matías Gulf coast, Argentina

Abstract

The understanding of how active aeolian coastal dunes transform into fully vegetated forms, and the specificdune configurations that emerge, particularly within coastal dune systems, is limited. This study examines thechanges in dune morphology associated with vegetation growth within transgressive dunefields in NE Patagonia,Argentina. The dunefields are located along the northern coast of the San Matías Gulf, ranging from relativelysmall to large, and dominantly active in the past ~80 years. Satellite and aerial images were analyzed using GISprocedures to calculate vegetation cover changes and dune migration rates and identify different dune types andtheir evolutionary stages of fixation. Five stages were defined in relation to vegetation cover and dune shapes andpatterns, from bare sand to fully vegetated dunes. Transverse or barchanoid ridges (sometimes with akl´e [fishscale], or chaotic patterns) convert to partially vegetated sub-parabolic dunes and finish as parabolic dunes. Inother cases, the dunes may convert to reticulate, akl´e, or chaotic patterns, completely vegetated. Various stagesspan a continuous range from unvegetated to fully vegetated dunes across a wide array of timeframes. In somecases, it was possible to recognize changes from stage one to five in ~20 years. Where the initial transverse duneis largely maintained during the stabilization process a distinctive pattern named “gusanos” (worms) was identified.The vegetated surface measured in some areas changed from 11 % to 51 % vegetation cover between 1961and 2022, with migration rates decreasing from 9.53 m/year to zero between 1991 and 2020. The increase invegetation growth also coincides with higher temperatures, weaker winds and decreasing grazing livestockwithin this Patagonia area. The recorded processes are similar to coastal dune and vegetation changes in somesemiarid regions from the Southern Hemisphere between 30 and 60◦ S, especially in South Australia.