ARCHIVED - Almost all living organisms below 3 metres in the Mar Menor died in October

The Spanish Oceanographic Institute blames agricultural activity and outlines the path to regenerating the lagoon

A study by the Spanish Oceanographic Institute (IEO) into the episode of anoxia which affected the Mar Menor in October concludes that the majority of the water in the lagoon below a depth of between 3 and 4 metres suffered an almost complete lack of oxygen, and that everything below that depth except for some bivalve molluscs died as a result.

This is what caused the appearance of tons of dead fish and crustaceans on the beaches at the northern end of the lagoon, and although the IEO study accepts that the immediate cause of the episode was the destructive gota fría storm of mid-September, which caused the run-off of freshwater, debris and fertilizers from the farmland of the Campo de Cartagena, it also mentions the “profound deterioration” over a period of decades due to agricultural activity, and warns that more “episodes of mass death” are possible “at any time”.

The study reports that “this extremely severe and prolonged episode of anoxia is the main cause of the almost total death” of living organisms below a depth of 3 metres, and of the migration of some species of fish which live near the sea bed to the surface.

However, the pocket of water with a low oxygen content has now shrunk significantly and is restricted to part of the northern half of the Mar Menor: in consequence it is valid to conclude that normal oxygen levels have been restored, although at the same time the data indicate that the amount of phytoplankton in the lagoon is increasing. This is leading to the water becoming greenish in colour, and also means that far less sunlight will reach the marine flora.

In attributing the recent ecological disaster in the Mar Menor to the agricultural activity of the last 30 years, the IEO refers to the episode of severe flooding in 1987. On that occasion more rain fell than in September of this year and the amount of run-off into the lagoon was greater, but there were no reports of fish dying en masse: in fact, fishermen reported that within a week the water was as clear as ever, while this time round after two months quite the opposite is true.

However, the IEO document looks not only at the past, but also at the future, outlining the path towards regenerating the Mar Menor in coming decades. The first step, as has been pointed out by many, is to stop the run-off of nutrients including nitrates from the crop fields in the Campo de Cartagena, and once this has been achieved to await the results. These could take a long time to become fully apparent because nutrients will continue to be released from sediments and aquifers for a period of years.

In addition, in order to help the Mar Menor to deal with the excess nutrients “measures based on nature” are suggested, such as recovering the wetlands around the lagoon or building artificial ones where floodwater will be retained. These wetlands are the only systems capable of retaining and eliminating nutrients in episodes of flooding which “will become more and more frequent due to climate change”, the report warns.

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