• Environment: Medusa, plankton and cement: the Mar Menor is in the UVI

As a strong cold capable of putting at risk the life of a chronic patient, the death of thousands of fish in the Mar Menor last weekend has revealed the weakness in which the Murcia lagoon is after the passage of the destroyer DANA.

Scientists and environmentalists debate whether the cold drop that hit Levante at the beginning of September has been the cause of the high mortality of animals or if, in fact, it is a consequence of the bad conditions with which the area faced the heavy rains, very punished by pollution resulting from agricultural practices and uncontrolled urban planning. A situation that they have been denouncing for years. At stake is the restoration of this unique place and that is replaced before another environmental disaster occurs again. The Minister for the Ecological Transition in operation, Teresa Ribera, who visited the area on Wednesday, said that we are facing an "extraordinarily traumatic episode" and "an environmental emergency, an evident proof of what happens when we look the other way." According to the minister, "there are no magic solutions, but you have to be very serious and rigorous" for the recovery of this "emblematic" space.

Ribera believes that the president of Murcia, Fernando López Miras, "is not in a position to demand", and although he celebrated "the will to work side by side" offered by the head of the regional executive, he advocated that each one assume the competition that corresponds to it, because "it is about adding and not replacing".

The Mar Menor extends along an area of ​​135 square kilometers of calm, shallow waters, which do not exceed six meters deep. Its salinity is changing, brackish, depending on the place and contribution of the light Mediterranean tides. This also depends on its interaction with the Cartagena de Campo aquifer and the seasonality of the ramblas, such as Albujón, which flows into it. The fragile balance of this marine and fresh terrestrial salt water system is responsible for its rich and at the same time threatened biodiversity.

In the Mar Menor and its salt flats, flamingos, coots, seagulls, eels, needlefish, seahorses, mújoles, sargos, chirretes and dorado live together. There are crabs, eels, hermits and 50 cm nacras, a very vulnerable mollusk. It is a space of the Natura 2000 Network. It is a Site of Community Importance (SCI), a Special Protection Area for Birds (ZEPA) and a Specially Protected Area of ​​Interest for the Mediterranean (ZEPIM). Its environmental management corresponds to the Autonomous Community of the Region of Murcia.

Many of the fish species of the Mar Menor live in the bottoms, hidden among the vegetation. This is the case of eel, lasbrids, blénidos, seahorses, mule fish and sole. They cannot live in the water column because they would be eaten by the sea bream and sea bass. Last week, when the oxygen in depth disappeared, the fish migrated through the bottom towards the banks looking for oxygen . There came a time when there were so many fish in the shallow areas that when they ran out of oxygen they had nowhere to go.

"There were fish literally jumping out of the water. The same thing has happened with the eyelids, coming out on the shore one above the other," Pedro García, director of the Southeast Naturalists Association (ANSE), says in a broken voice. "The situation is dramatic," he said. "Not only have thousands of fish appeared dead on the banks, they are of all species and sizes including tiny fry, so not only the fish that could be caught by the fishing fleet this year has been lost, but in some species , the one of several following years, as it is the case of the eels ".

Juan Manuel Ruiz, a scientist at the Spanish Institute of Oceanography and a member of the Scientific Committee of the Mar Menor, provides very high fish mortality data. " All living beings have died from three meters deep , which could represent 70% of the total surface of the bottom of the lagoon," he said. The figure is calculated taking into account the extent of the anoxic layer below three meters deep and taking into account the observations of the affected areas. However, it is not a data shared by all the experts of the group, who believe that this information could be premature.

The explanation of what happened in recent days is in the reservoir - due to heavy rains - of brackish water and little dense on the salt water body. Two layers formed that did not mix and left the funds without oxygen. The effect was not seen immediately, but its ravages began within a few hours, although the magnitude of the disaster has not been perceived until almost a month after DANA: the death of three tons of fish and crustaceans. However, to understand why in similar episodes of similar heavy rains there have been no similar deaths, we must look at the Campo de Cartagena, its extensive agriculture and an aquifer overflowing with contaminated water.

" The problem of the Mar Menor is the relationship it has with an aquifer heavily contaminated by nitrate, " explains José Luis García Aróstegui, senior scientist at the Geological and Mining Institute of Spain. This is the Quaternary Aquifer of the Campo de Cartagena, which receives what comes through the infiltration of rain and irrigation water. When rainfall is important, there is a lot of surface runoff and a lot of water entering the aquifer. Its exit is towards the Mar Menor and towards the Mediterranean or towards the wells of the farms when the water is pumped.

Historically, the level of the aquifer has risen and, therefore, its discharge to the Mar Menor. "The levels are now very high. In some areas there is even suffocation of the roots of the plants, since the groundwater is only a meter or a meter and a half from the surface," said the hydrologist. The researcher has developed a three-dimensional model in which he compares the situation of decades ago with that of now and concludes that the system has been filled.

The Mar Menor is an inland sea, an lagoon that encloses the Mediterranean by an arm of 21 kilometers of white sands and mobile dunes. It doesn't catch him at all. La Manga is open to what the locals call the Mar Mayor and both waters communicate and mix through several channels: the goals. It is crowned to the north, the salt mines of San Pedro del Pinatar. To the south, the last shot of the Betic Cordilleras, Cabo de Palos, from the Latin palus, in reference to the word lagoon. To the west cities, towns, beaches and urbanizations alternate with orchards and rural lands. To the east, the tourist landscape of tall buildings barely lets air pass. There is no free gap. In the center, the islands of Barón, El Ciervo, Perdiguera, Rondella and del Subject are ancient volcanic cones and the last virgin redoubts of the area.

The Mar Menor is supported by the aquifer itself, which also surrounds it completely. Below it, the groundwater is saline. While the water sheet of the Mar Menor has a depth of between four and six meters, that of the aquifer is 50 meters.

In the terrestrial part, the groundwater of the aquifer is brackish and cannot be used directly for irrigation. To meet the demand of agriculture when there is no water from the Tajo-Segura transfer, evictors have been used. The process causes low salinity brine but very high nitrate content that needs to be denitrified before pouring its content. This process is very expensive and is part of the Zero Discharge Plan that the Ministry for Ecological Transition (Miteco) prepares next to the Region of Murcia.

Views of the Mar Menor captured by the Sentinel satellite on September 3 (above) and September 13 (before and after DANA) .COPERNICUS

The Zero Discharge Project, prepared by the Ministry for Ecological Transition (Miteco) and the Ministry of Water, Agriculture and Environment of the Region of Murcia, identifies the pressures suffered by the area due, above all, to an unsustainable agricultural model . According to Miteco sources consulted by this means, it cites the over-elevation of the groundwater level of the Cartagena de Cartagena aquifer, as a consequence of irrigation tasks; nitrate contamination of agricultural fertilizers from surface and groundwater, which end up in the Mar Menor; and overexploitation of aquifers by wells that return contaminated water and brine to the system.

This situation is aggravated when torrential rains that carry land and pollutants to the sea or extreme phenomena such as the DANA last September, which flooded the area and severely affected the lagoon. Therefore, this project includes 21 types of actions. Of these, three depend on the Miteco and the rest are the responsibility of the Region of Murcia and the community of irrigators.

The measures that depend on the ministry consist in establishing the regime of exploitation of the mass of the aquifers, quantifying the underground discharge that reaches the Mar Menor and the environmental recovery of the coastal spaces. For its part, the region of Murcia must administer the productive model, control irrigation rejection water, livestock waste or irrigation returns.

Since December 2018, the Segura Hydrographic Confederation has established 24 sounding points to monitor the volume of groundwater that reaches the Mar Menor. The analyzes will conclude in early 2020 and monitor a three-kilometer strip from the coastal edge of the lagoon inland, from north to south, between the towns of San Pedro del Pinatar and Cabo de Palos.

Operators collect dead fish in San Pedro del Pinatar (Murcia) last Monday.

"Throughout this summer, the Confederation has made a series of bathymetry surveys to calculate the amount of water that passes from the aquifer to the Mar Menor and see how to act. The possibility of pumping from the aquifer of the Campo de Cartagena to try to download it, "the press office of this organization has confirmed to this newspaper.

For Ángel Pérez Ruzafa, member of the Scientific Committee of the Mar Menor, the key is also to control the water table. "I am convinced of that. Without a control of what happens with the water in the drainage basin we will not have management capacity," he argues. According to the biologist, regardless of whether agriculture is controlled so that it is reasonable and urgent measures are complied with - including the installation of hedges, which avoid fertilizing in times of greatest risk of torrential rains - these will be insufficient if there is a high water table that enters the Mar Menor, and there is no water collection system.

"If we had done this before, the consequences of the DANA would not have been so intense and we would be in better conditions for the next one. We also have to count on it, because we are in a context of climate change in which these types of events are going to be more and more frequent, "adds Pérez Ruzafa.

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