Mar Menor: cleaning Europe's largest saltwater lagoon

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Mar Menor, Europe's largest coastal saltwater lagoon, faces severe contamination from pesticide runoff (Credit: Getty Images)
Mar Menor used to be a Spanish treasure until pesticide runoff and sewage turned it into a green soup. Can local activists help restore it?

When Eladio Sánchez Egea returned home one evening in April 2020, after working another long day in the field, he found his 11-year-old son agitated. At school that day, the boy had been told the agricultural industry was responsible for polluting the waters of Mar Menor, s largest coastal saltwater lagoon which borders the Mediterranean Sea in the Iberian Peninsula, in southeastern Spain. "This is your fault, you are responsible for destroying our home," the boy told Egea, who works as an organic farmer. Egea was upset, although not at his son. "I was angry at how people perceive us farmers," he recalls. "Everyone blames us for the pollution in Mar Menor instead of assuming collective responsibility."

Over the past four decades, the Mar Menor has faced severe contamination from an excess of nitrate and phosphate, chemicals typically found in the fertilisers used in the neighbouring Campo de Cartagena, the largest agricultural croplands in the region. This contamination has led to several ecological collapses, pushing endemic species, such as the Spanish toothcarp, or Iberian killifish, to the brink of extinction. After decades of inaction and scientific warnings, local authorities have slowly been introducing both restoration and prevention measures in the hopes of saving the lagoon.

In recent years, fishermen have been catching more algae than fish in the Mar Menor (Credit: Ecologistas en Acción)

In recent years, fishermen have been catching more algae than fish in the Mar Menor (Credit: Ecologistas en Acción)

These steps either deal with the consequences of the pollution, for instance, organising cleaning efforts to fish out the algae from the lagoon. Alternatively they can directly target the source of the pollution. This can include?legislation limiting the use of inorganic fertilisers, directing farmers to plant hedges that act as natural barriers reducing the flow of nutrients and prevent soil erosion, and clamping down on illegally irrigated lands to regulate the use of water for agricultural purposes. But despite a?recent improvement of the lagoon's ecosystem, experts warn that this may be short-lived, and more drastic action is needed to reverse the damage.

In the early hours of an already hot morning in March, the first rays of sun stroke the waters of Mar Menor. The distant call of seagulls flying across the beach announces the sunrise. It should be an idyllic scene, but instead of clear, shimmering waters, the lagoon is a dank, murky green. Once known by locals and tourists as "the crystal sea" for its pristine waters, Mar Menor has since been dubbed the "green soup". In recent years fishermen have been catching more algae than fish, lining the shore with green triangular piles. For Mariló Jiménez Huescar, a local from San Javier, a town located four miles (7km) from Mar Menor, the lagoon is part of her social identity. "I used to go to the beach every summer, and the lagoon has always been a part of my life," says the 26-year-old.

Gasping for breath

Once a thriving ecosystem home to unique species such as the endangered long-snouted seahorse, the severe contamination of Mar Menor is not new. Following four decades of rampant urban development, regulatory mismanagement, and the rapid expansion of livestock and agricultural production, a stream of nitrogen and phosphorus has steadily flowed into the lagoon. "The lagoon has spent 20 years enduring this pressure," explains Miguel ángel Esteve, a professor of ecology at the University of Murcia in Spain who has been studying the Mar Menor since the late 1990s.

I was angry at how people perceive us farmers. Everyone blames us for the pollution in Mar Menor instead of assuming collective responsibility - Eladio Sánchez Egea

In 2016, the ecosystem collapsed. The excess of nitrogen and phosphorus led to the lagoons eutrophication, a process where a surplus of nitrates leads to the rapid and widespread growth of algae that feed on them. Studies have shown that as global temperatures keep rising, increased water temperatures can also stimulate the growth of these blooms. The algal blooms –?some of which can be?harmful to humans and animals – covered the lake's surface, preventing sunlight from penetrating the water. This stopped plants growing in the water from photosynthesising, while marine species struggled to find oxygen.

The contamination of Mar Menor has led to widespread protests across Spain (Credit: Getty Images)

The contamination of Mar Menor has led to widespread protests across Spain (Credit: Getty Images)

"It's as if the lagoon was gasping for breath," says Esteve. The lagoon turned from a clear oasis brimming with life into a "green soup", he says. In 2016, 85% of the lagoon's vegetation died. Species like the large fan mussel have almost gone extinct. Three other collapses have followed in recent years. Among the most dramatic consequences of eutrophication are episodes of asphyxiated fish, like the ones locals witnessed in August 2021 when more than five tonnes of dead fish were washed ashore.

The lagoon's environmental degradation has not only affected its biodiversity. The hospitality, housing, and fishing sectors bore the brunt and residents no longer recognised a beloved summer spot. "I could not swim in the lagoon anymore because the water surface was covered with green algae," says Huescar. The strong stench of decomposing algae and rotting fish stopped both locals and tourists from entering the water. Huescar decided to take action and participated in her first demonstration against the pollution in December 2019.

Widespread protests

Even before Huescar joined the demonstration, the public outcry led to several protests in cities across Spain. But it was only in 2018 – the same year the EU Commission sent a notice denouncing the Spanish governments failure to protect the water with nitrate levels well above the legal limit of 50 mg/litre – that the regional government and the Hydrographic Confederation of Segura River, the body in charge of the administration of public water resources,?introduced a bulk of recovery measures.

It's as if the lagoon was gasping for breath – Miguel ángel Esteve

These included clamping down on illegally irrigated croplands, and restoration efforts such as the fishing out of algae. The latter, however, is contested by experts like Esteve, because while it temporarily cleans its waters, it in the Mar Menor in the long-term. Nat Llorente Nosti, an activist for the non-profit Ecologistas en Acción, states that between the summer and the end of 2022 £5m (€6m/$6m) was spent on employing fishers to remove over 20,000 tonnes of algae. As of August 2023, a total of £14.3m (€16.6m/$17.5m) has been spent. "The government should have dedicated these funds for a better use…to tackle the main source of contamination instead of clearing the water to make it look appealing from the surface," says Nosti.

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The main industry targeted by new interventions is the agricultural sector. "So far, I've been impacted by four measures, some of which we were already practising but others are new, like the planting of hedges," says Egea. On his 24 acres (10 hectares) of farmland where he mainly grows peppers, celery, and pumpkin, the hedges act as natural barriers, filtering nitrates from fertilisers and preventing soil erosion.

The other steps Egea has implemented are the collection of rainwater – both for irrigation purposes and so it doesn't absorb nutrients and flow into the lagoon – regular checks by public officials to ensure solutions are adequately implemented, and the use of pressure monitors (agricultural devices which allow the precise application of fertiliser or water), he says. The farmers are legally required to have two in each section of their cropland. Egea says that the monitors provide crops with the precise amount of water, avoiding overwatering.

Agricultural runoff and sewage has turned the Mar Menor into a "green soup" (Credit: Ecologistas en Acción)

Agricultural runoff and sewage has turned the Mar Menor into a "green soup" (Credit: Ecologistas en Acción)

Many farmers, such as Egea, feel resistant to implement these changes as they don't understand how they will help improve the health of the lagoon. So far, no widespread assessment has been published on how effective the measures are, although Esteve is currently undertaking research.

While Egea has at times felt unjustly vilified as a farmer, experts like Nosti are adamant the interventions should target the agricultural sector. This is because up to 85% of the nutrients come from the livestock and intensive agricultural sector, mostly from fertilisers used in the lands of the Campo de Cartagena – more than 148,286 acres (roughly 60,000 hectares) of croplands lying to the west of the lagoon. Known as "Europe's orchard", over 60% of the fruits and vegetables grown in the Campo are exported, 21% to the UK alone. Exports to the United States have doubled in the first half of 2023 compared to the previous year, reaching a total of €2.2m (£1.9m/$2.3m). Besides the agrarian sector, studies find that around 15% of nutrients come from urban activity, such as sewage waters.

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In order to bring that number down, a single action is not sufficient, says Javier Senent Aparicio, a researcher?who studies the flow of water streams at the Catholic University of Murcia, in south east Spain. "The Mar Menor is a complex ecosystem. That is why several measures have to be applied in conjunction," he says, hoping to draw the attention of the authorities to the critical situation of the lagoon.

In particular, there are eight specific measures that, combined, are the most successful, a 2023 study found. The study conducted as part of the European Union-funded research project Smart Lagoon by Aparicio and his colleagues found that, together, the measures can reduce the flow of nutrients by around 70% – "with nitrate exports being reduced by 67% and phosphorus exports by 75%". Six of these eight interventions directly target the croplands.

Most nutrients flow into the lagoon from superficial water streams that run from the farmlands down into the lagoon, especially during heavy rainfall, says Esteve. A smaller part of the nutrients that flow into the lagoon, around 25%, he says, come from the Cuaternario aquifer, where nutrients have been seeping in over decades. The aquifer does not naturally store potable water, but it is used for irrigating farmands. The aquifer holds underground streams which directly flow into the Mar Menor. In March 2023, Esteve estimates that an average of five metric tonnes of nitrates were flowing into the lagoon every day." Around 4,500 to 5,000 tonnes of nitrates a year, both from superficial and underground discharges."?

The contamination of Mar Menor has led to several ecological collapses and pushed species to the brink of extinction (Credit: Getty Images)

The contamination of Mar Menor has led to several ecological collapses and pushed species to the brink of extinction (Credit: Getty Images)

Among them is the planting of hedges, but the study also analyses bigger-scale measures such as contour farming and the creation of shoreline buffers. Contour farming involves ploughing and planting rows that follow the natural contours of the land. "Installing hedges and following contour farming are among the most effective solutions in reducing nutrients exports because they help to slow surface runoff, trap sediments and absorb nutrients, especially during intense rainfalls," Aparicio explains. These larger scale solutions, however, have yet to be implemented.

So-called shoreline buffers, for instance in the form of wetlands, act as natural filter barriers. In Murcia, the Ministry of Ecological Transition announced in 2021 the creation of a green belt around the coast of the Mar Menor. The belt will include three semi-natural wetlands, whose implementation has been postponed to March 2024 and is expected to retain over 80% of waters flowing into the lagoon. A 2019 report found that nature-based solutions like wetlands could retain between 66% and 98% of nutrients, although Aparicio adds that these measures should be combined with other best management practices to achieve any significant improvement.

Additional measures that farmers are obliged to carry out include a limitation on the use of fertilisers, the main source of nitrate. The problem, though, is not just the use of nitrate-heavy fertilisers, but the extent of its use. For decades, the region has seen an uncontrolled expansion of agricultural activity, much of it unregulated. Despite numerous environmental laws and protections, it was only following the 2020 Law for the Recovery and Protection of the Mar Menor that authorities started clamping down on illegal croplands. Non-profits estimate these made almost 30,000 acres (12,000 hectares) of land, overexploiting the aquifer in a region where droughts are more and more frequent. So far, authorities have clamped down on?over 8,900 illegally irrigated hectares (nearly 22,000 acres), forcing many farmers to switch to rain-fed agriculture, and helping control overwatering, which leads to soil run-off into the lagoon.

Of the £417m (€484m/$506m) assigned by the Ministry of Ecological Transition to fund the recovery of the Mar Menor by 2026, around £43m (€50m/$52m) had been spent by March 2023 on these actions as well as research and conservation efforts. The additional funding will go towards research and implementing nature-based solutions to restore the lagoon, like wetlands.

The water is clear again, people are starting to return to the beach – Mariló Jiménez Huescar

Aparicio says that combining these measures, particularly nature-based solutions, is the most effective approach to tackle the nutrient pollution at its source. "Though planting hedges and contour farming are most effective, these measures should be combined with other best management practices to achieve significant improvements," he says. In terms of costs, nature-based solutions are also the most cost-effective, according to a study co-authored by Esteve. "All of them act as buffer zones and retain nutrients and pesticides from the Campo de Cartagena. [These measures] are developed, well-known, easily implementable and of low cost," the study authors conclude. For instance, "the restoration of wetlands is comparatively more cost-effective than other types of measures such as the collection of drainage with civil engineering infrastructure to reduce diffuse pollution in agricultural fields".

Farmers in need of support

The implementation of the measures has represented an additional financial burden to farmers. "We have done everything the authorities asked us," Egea says. "Some measures like the hedges cost us €2,000–3,000 (£1,700 - £2,500 / $2,150 - $3,220) per year. These are additional costs and we have not received any direct support from the authorities."

Nosti does recognise the financial burden faced by farmers. "Small farmers should be provided with financial support and necessary training to adopt organic farming practices."

However, since 2020, ?over 350 cases have been filed against farmers for not following compulsory measures. "I am willing to follow regulations," Egea says, "but I would like to receive some compassion from the authorities instead of being blamed for the contamination of the entire Mar Menor."

The strong stench of decomposing algae and rotting fish has stopped both locals and tourists from entering the waters of Mar Menor (Credit: Ecologistas en Acción)

The strong stench of decomposing algae and rotting fish has stopped both locals and tourists from entering the waters of Mar Menor (Credit: Ecologistas en Acción)

Nearly seven years after the first collapse of the lagoon, nutrient levels seem to have improved, the latest report by the Spanish Institute of Oceanography found. By the end of July 2023, around 1.7 tonnes of nitrates were flowing into the lagoon per day, a decrease compared to previous numbers of up to six tonnes per day. Yet the report highlights the apparent stabilisation "should not be interpreted as … a clear sign of an improvement in the general state of the ecosystem". Instead, it adds, improvements could be due to the lagoon's own complex control mechanisms and capacity to autoregulate.

And so, despite the seeming improvement of the lagoon, non-profits and locals like Huescar are still concerned. "The water is clear again, people are?starting to return to the beach," he says. "But the authorities are not taking care of other sources of contamination like the massive urban development for tourists or the sewage systems."

While a full restoration of the lagoon is unlikely, experts are hopeful that there is a future for the Mar Menor. If the combination of measures are implemented adequately, Esteve says, it would allow the lagoon a respite to recover. "We will probably not be able to get back the same ecosystem," he says. Fauna and flora within the lagoon have changed as a result of human activities, trying to adapt to the entry of additional nutrients, minerals and invasive species. "But we hope to recover a similar Mar Menor," Esteve says.


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