The Mar Menor has entered anoxia situation Following the passage of DANA Alice, a drop in oxygen levels in the southern basin is threatening seabed organisms. Monitoring teams warn that the outcome will depend on how the system evolves in the coming days.
According to the latest reports from the IEO-CSIC and Miteco, the decisive factor is exposure time at these very low oxygen levels, while the Belich project maintains continuous monitoring and sampling at the most sensitive points of the lagoon.
What happened and where it is most serious
Torrential rains injected large volumes of fresh water and sediment, causing a stratification of the water column which prevents mixing between the surface and the bottom and reduces the supply of oxygen to the deep layers.
The sensors place the focus on the southern basin, where in the deep layer the oxygen has fallen to 1,5 mg / L, values typical of anoxia; the northern zone, however, has been less affected by the Mar Menor's characteristic circulation pattern.
The records identify two main pulses entrance: one at the end of the 10th through the channels of the southern basin and another, at dawn, through the northern area at the height of San Javier, altering salinity, turbidity and the internal dynamics of the lagoon.
In parallel, since the 12th a strong increase in phytoplankton has been observed, a scenario of “green soup” which darkens the bottom and intensifies oxygen depletion, especially when the stable atmosphere maintains stratification (which reappeared and consolidated from day 14).
What the measurements say
Buoys, landers and profiles with CTD corroborate the decrease in oxygen at the bottom and a notable decrease in salinity In the surface layer of the southern sector, a pattern that has remained stable for several days according to the most recent vertical profiles and sampling.
The IMIDA network, with 21 control points, describes a general trend towards stabilization: average oxygen level of 7,21 mg/L and salinity of 43,08 PSU, with the exception of four stations in the southern basin that have lower oxygen levels compared to the rest.
The latest data show an improvement in transparency up to 2,75 m and a high but contained turbidity (7,98 FTU), while chlorophyll decreased by 42% compared to the first measurements after the storm, without this neutralizing the inertia of the episode at the bottom.
In addition to the direct impact of floods, technicians and scientists insist that the aquifer maintains continuous contributions of water and nutrients that intensify after episodes of rain, a structural factor that determines the recovery of the system.
Risks and response underway
These low oxygen concentrations are toxic to fish and vegetation; For now, there are no reports of mass die-offs, but the risk increases the longer the episode continues in the deep southern layer.
A change in the weather that breaks the stratification—sustained wind or a storm that favors the vertical mix—would accelerate oxygen recovery; however, prolonged atmospheric calm could worsen the situation.
The Belich project teams (IEO-CSIC, CEBAS and Tragsa) are working on crisis cabinet mode, with continuous monitoring and sampling to assess effects on wildlife, from behavioral changes to possible mortality episodes if conditions persist.
At the institutional level, there have been cross-reactions between administrations and political parties on aquifer control, management of gullies, and pending planning, while the scientific committee meets to update the diagnosis and coordinate measures.
The Mar Menor faces a fragile episode Marked by anoxia in the southern basin, “green soup,” and persistent stratification, what happens in the coming days—whether there is mixing or stability continues—will determine whether the ecosystem avoids another die-off or relives scenes no one wants.
