New research uncovers cause of Mar Menor's mysterious white stain
While it might appear harmless, the murky patch has caused serious damage to the Murcia lagoon
A team of scientists from the Spanish Institute of Oceanography (IEO-CSIC) has released a detailed study on the unusual white stain that first appeared in the Mar Menor in the summer of 2022. Published in Science of the Total Environment, the research explains what caused the water to turn become bleached, a phenomenon known as "whiting."
The research builds on preliminary conclusions released in 2024, which had already linked the appearance of the murky white patch to calcium carbonate precipitation. This means that tiny crystals formed when minerals in the water reacted under certain conditions and these crystals made the water look milky white.
Now, after an in-depth analysis involving water chemistry, sediment composition, organic matter and phytoplankton dynamics, researchers have been able to fully explain the phenomenon.
According to the study, the white stain is made up of microscopic calcite crystals formed directly within the Mar Menor. Using electron microscopy and isotopic testing, the researchers were able to prove that the crystals originated in the lagoon itself, not from external sediment or runoff.
The root causes of the bleaching, according to the team, lie in long-term changes to the Mar Menor lagoon. Alterations such as a rising water table and higher carbonate levels in the groundwater are believed to have shifted the pH of the lagoon waters, triggering the calcium carbonate precipitation.
While a little murky patch in the water may sound harmless enough, the ecological impact is actually very significant.
"The opacity of the water in the area of the slick has prevented the passage of sunlight, causing the complete disappearance of marine vegetation meadows," explained Juan Manuel Ruiz, head of the BELICH project.
"This research demonstrates, once again, the profound connection between the health of coastal ecosystems and the management of water resources and the land use in their catchments," he added.
The study was a collaborative effort between various IEO oceanographic centres including those in Murcia, the Canary Islands, Málaga and A Coruña, as well as several other CSIC-affiliated institutions such as CEBAS, IPE and IACT.
All are part of the BELICH project, which is dedicated to studying, monitoring and ultimately protecting the Mar Menor ecosystem.
Image: Instituto Español de Oceanografía
