A transient coastal wetland: from estuarine to supratidal conditions in less than 2000 years—Boca do Rio, Algarve, Portugal

Abstract

Palaeoecological analysis of a 3 m sediment core from a coastal site in the western Algarve, near Lagos, Portugal, reveals the changing ecological characteristics of the wetland environment during the late Holocene. The dinoflagellate record and sedimentary characteristics show that approximately 2000 years ago the modern Boca do Rio wetlands were an estuary. By about 1200 14 C years BP, transition to a lower energy environment was taking place. The pollen record at this time indicates the existence of typical salt marsh vegetation. There is a likely hiatus in the sedimentary record caused by the tsunami associated with the Lisbon earthquake of AD 1755. A barrier lake, impounded by tsunami deposits, existed for approximately 60 years before being breached, followed by a reoccurrence of saline conditions. A comparison of the mineral magnetic signature of the sediments with that of soil samples from the catchment suggests a relatively local provenance for some of the sediments, rather than the highly erodible Carboniferous rocks of the Algarve's / / / Serra uplands. However, it is also suggested that there is a biogenic component to the magnetic mineralogy. Coastal wetlands are among the most vulnerable Mediterranean environments. The history and future of the Boca do Rio wetlands is examined in the context of alluviation history, rising sea levels, both past and future, and catchment land use. Changing patterns of cultivation, irrigation and land abandonment during the last 50 years are likely to have increased water demands within the catchment and therefore decreased river discharge to the wetlands. Consequently, the continued existence of the wetlands in their present form is in doubt, despite being part of a protected natural park.

Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast, Southern Portugal

“…The decrease of the intertidal area within the estuaries of Algarve occurred during the terminal phases of alluviation during the Late Holocene. Chester and James (1991) and Allen (2003) attribute this process to anthropogenic causes, i.e. forest cutting and agriculture which are documented throughout seven millennia of prehistoric, Roman, Moorish and Portuguese occupation.…”

Pleistocene and Holocene geomorphological development in the Algarve, southern Portugal

“…Sites from the Copper Age are found at Alcalar in the central Algarve and Santa Justa near to Alcoutim (Fig. 1), but by the early Bronze Age a Dias and Taborda, 1988;Dias and Neal, 1992;Dias et al, 2000;Pereira et al, 1994;Zazo et al, 1994Zazo et al, , 1996Boski et al, 2002;Allen, 2003;Moura et al, 2007;Ferreira et al, 2008;Matias et al 2009;Schneider et al 2010 and the references cited in the table). (c) Principal geomorphological events in the inland valleys.…”

“…Common mollusca included Monodonta lineata (turban), Patella (limpet), Mytilus (mussel), Pollicipes (barnacle) and Thais haemastoma (dog winkle/drill) (Bicho, 2009). Human population numbers are unquantified, but are inferred to have been low; and in neither the Epipaleolithic nor the Mesolithic was the impact on the environment significant (Allen, 2003;Bicho, 2004;Bicho and Haws, 2008).…”

Islands of biogeodiversity in arid lands on a polygons map study: Detecting scale invariance patterns from natural resources maps

“…However, such construction projects threaten to devástate many riverbeds with consequent risk ofextinction to plant species and the ecological communities that depend on them (Sprenger, 1999;Alien, 2003;Kudray and Schemm, 2008). Likewise, the fast expansión of tourism residences and greenhouse crops in Almería are additional serious threats to the habitat's vegetation and to vascular plants near coastal lands (e.g.…”

“…Likewise, the fast expansión of tourism residences and greenhouse crops in Almería are additional serious threats to the habitat's vegetation and to vascular plants near coastal lands (e.g. sands, dunes, some halophytic PNV and saltmarshes) (Alien, 2003;Castro et al, 2011;Domínguez-Beisiegel et al, 2013). Both habitats cover small áreas within the study área, but host a considerable part ofthe area's biodiversity.…”