4500 years ago, while the great pyramids of the Giza Plateau were being built in ancient Egypt, the sea level in the Vigo estuary was significantly lower than today and in the Cíes Islands, a precious treasure of the Galician coast, what is now known as Lagoa dos Nenos, one of the most valued ecosystems in the archipelago, did not yet exist. This resounding statement is one of the main conclusions of a multidisciplinary study launched by the Sedimentary Basin Analysis group of the University of Vigo (Basan group), with the collaboration of scientists and historians from other groups at the universities of Vigo, Santiago de Compostela, León and the Canadian University of Victoria. “The results have allowed us to understand that during the last 3000 years the evaluation of the emerged basin located between the islands of Faro and Monteagudo has been much more complex than we believed until now”, explains one of the authors, Castor Muñoz Sobrino, a member of the Basan group.
The study, recently completed and already published in scientific media, shows that, unlike what was thought until now, the Lagoa dos Nenos is a system of relatively recent origin, ephemeral and almost permanently threatened by the combination of climate change, sea level variations and human action. “In its place there was a coastal freshwater lagoon, with abundant floating aquatic vegetation and a border of reeds, alders, hazels and willows”, explains the researcher, who also emphasizes that a strip of coastal dunes separated the lagoon from the beach and the sea.
Progressive rise in sea level
To reach this conclusion, the authors of the article explain that almost a decade ago different multidisciplinary studies helped to understand the dynamics of the main ecosystems of the islands during a period between 7000 and 3700 years, and also the origins of the current lagoon. “For less than 3700 years ago, the progressive rise in sea level has been changing the type of materials that were deposited in the basin located between the two islands and, as the level of the beach rose, the dune system also retreated inland”, emphasizes Muñoz Sobrino, while explaining that the old sediments of the lagoon were covered at some point by coarse sand and fragments of shells that, over the centuries, were removed by wind, tide and storms. “Logically, the conclusions that can be drawn from the study of these materials are more diffuse: they can help us get an idea of the general evolution of the lagoon, but they do not clarify many details about its most recent history,” he adds.
There were active freshwater coastal ecosystems until the late 15th century.
Taking into account this background, the Vigo group launched a multidisciplinary study, the results of which confirmed that for centuries, and before the current lagoon was finally formed, ecosystems of dunes, coastal marshes and wetlands of brackish and fresh waters coexisted in that space. During the colder phases, with lower sea levels and less intense storms, the dune systems expanded until they disconnected the coastal lagoons from the sea. “Specifically, we can now specify that there were active freshwater coastal ecosystems, at least until the time when Columbus traveled to America, at the end of the 15th century”, underlines Muñoz Sobrino.
As also demonstrated in the study, funded by the Ministry of Education and Science and the Xunta de Galicia, the combination of certain conditions (warmer or stormier periods) caused the opening of drainage channels and the greater contribution of materials of continental origin to the sea affected the trophic conditions of the waters surrounding the archipelago. They determined that this occurred during the first half of the 20th century, but also during the Roman Warm Period, around the change of Era. “However, the most important of these episodes seems to have occurred during the 13th and 14th centuries”, emphasizes the researcher, who relates this to the fact that this would be the historical period of greatest agricultural production, livestock activity and human impact recorded on the islands, due to the apogee of the two monasteries located on them. “From that moment on, these local communities began to decline, until the monasteries were abandoned in the mid-18th century,” adds the researcher, who also states that in reality, both the islands and most of the area around the Vigo estuary were already practically deforested by the 16th century, so that the increase in erosion also contributed to reactivating the systems of coastal sands and dunes.
“In short, the new results have allowed us to understand that during the last 3000 years, the evolution of this ecosystem has been much more complex than previously believed,” emphasizes Muñoz Sobrino, who insists that this entire process was “neither unidirectional nor continuous” and the new evidence indicates that throughout this time several relevant environmental modifications have occurred in the area, most of which were produced by changes in climatic and oceanographic conditions, but also influenced by the history of human occupation on the islands and on the banks of the Vigo estuary.
Basan, a multidisciplinary team in which geologists, botanists, biochemists…
The Basan group (Basin Analyses, XM-3: University of Vigo) is a multidisciplinary team formally established in 2007, with the intention of creating a stable, multidisciplinary research group, but with common objectives and lines of work, capable of promoting collaboration with other complementary lines and research groups, both at the University of Vigo, and at the University System of Galicia and other national or foreign institutions.
The research that has been developed by the group over the past few years ranges from the comprehensive study of basins to the high-resolution characterization of their sedimentary fill. Led by Professor Soledad García Gil, the group currently includes a dozen researchers who work in several interrelated lines of work, since the group includes geologists, botanists, edaphologists and biochemists. “For this specific work, whose IP was the group director, we used data collected in several projects that we have developed since we were established as a group,” points out Muñoz Sobrino.
For more information, see our blog: https://oceanoecimat.wordpress.com/2016/05/07/tres-mil-anos-de-cambios-ambientales-en-el-complejo-playa-duna-lagoon-de-las-islas-cies/
