Located in the Brunswick Peninsula, in the Magallanes Region, the San Juan de la Posesión River is one of the main tributaries of the Strait of Magellan. Its mouth, at Punta Santa Ana, was the focus of a study that challenges expectations about the relationship between river flow and water salinity.
Since 2018, scientists from the Center for Research in Dynamics of High-Latitude Marine Ecosystems (IDEAL) at the Austral University of Chile (UACh) have been monitoring the area with an oceanographic station installed at the river’s mouth. Currently, a recent article published in the journal Regional Studies in Marine Science revealed unexpected findings about water dynamics in the area.
The Wind, a Key Factor in Water Salinity
The study, led by Dr. José Garcés-Vargas and marine biologist Vicente Aravena, found that the San Juan River flow does not have a direct relationship with salinity reduction, which contradicts common theory.
“It would be expected that a higher river flow, being freshwater, would reduce salinity in the area, but surprisingly this did not happen,” explained Dr. Garcés-Vargas.
The researchers determined that the wind plays a crucial role in this process. Depending on its direction, it can expand or contract the freshwater plume, thus affecting the salinity of the water column. Additionally, it was observed that the greatest salinity changes occur in the first five meters of depth, while in deeper layers, the variation is minimal.
Another significant discovery is that subsurface water in the area comes from the Pacific Ocean, which contributes to maintaining a relative stability in salinity conditions.
Impact on Biodiversity and Climate Change
Changes in the water column structure directly affect marine organisms in the Strait of Magellan and the salinity of the San Juan de la Posesión River. “When the water is stratified, barriers are created that can hinder the movement of some species,” explained Garcés-Vargas.
Many organisms depend on specific ranges of temperature and salinity to survive. If these parameters are altered, certain species may not adapt, leading to a reduction in their populations.
The study also warns about the impact of climate change, which could further alter the dynamics of the San Juan River. Increasing winds and melting ice would affect the water structure, with direct consequences for marine ecosystems and the communities that depend on them.
Given that the area has been requested as an Indigenous Marine Coastal Space (ECMPO) by the indigenous community Kawésqar Nomadic Family Groups of the Sea and Atap Indigenous Community, research like this is key to their preservation.
“These studies help us better understand the importance of the area, not only from a scientific and conservation perspective, but also for the indigenous peoples who depend on its marine resources,” concluded Aravena.
