Impacts of sand extraction and deposition on the ecosystem recovery rate in the southern coastal zone of Portugal

Artificial nourishment of sandy beaches using sediment from borrow areas located on the continental shelf is increasingly a recommended solution for reversing the erosion process that affects the coastal zone. However, the impact of sand extraction in the shelf and deposition on the beach on the benthic communities (structure and functioning) is still poorly known, contributing to the lack of information needed for the assessment of Descriptor 6 (Sea-floor integrity) of the Marine Strategy Framework Directive (MSFD).

The aim of this work is to evaluate the morphological and ecosystem impacts of sand extraction at the inner shelf, as well as the consequent impacts of sand deposition at the nourished beaches. In this context, short-term and long-term monitoring activities based on a multidisciplinary approach were implemented at new and former borrow areas located in the southern Portugal (Algarve) inner continental shelf and adjacent beaches. These activities include multibeam bathymetric surveys complemented by surface sediment sampling, wave and current measurements, and a fluorescent tracer-marked sand experiment. Moreover, benthic macrofauna composition and structure are being studied at borrow areas (former and new) and at the nourished beaches. The acquired data allow a first assessment of the recovery rates regarding the sea-bottom morphology and benthic communities, and contribute to a better understanding of the involved processes.

The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and ECOEXA project (MAR-01.04.02-FEAMP-0016)