This Project Is Helping Tackle Eutrophication in the Mediterranean Sea

Implementing solutions focused on prevention, mitigation, and restoration can curb the transport of surplus nutrients, such as nitrogen and phosphorus, from terrestrial environments to the ocean, reducing the risk of ecosystems eutrophication in the Mediterranean.

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Many of the nutrients found in fertilizer products for agricultural growth, such as nitrogen and phosphorus, are washed by runoff, which then flows into the sea through river networks. These nutrients can also enter waterways through the effluent released from sewage treatment plants. When present in excess, they can disrupt aquatic ecosystems and trigger something known as eutrophication.

What Is Eutrophication?

When nutrient levels become excessive or unbalanced, algae can proliferate rapidly in aquatic environments. This triggers a series of cascade effects, leading to reduced oxygen levels, which may cause the death of fish and other organisms. This phenomenon is called eutrophication.

Nutrient pollution can be point-source from sewage treatment effluents – when nutrients originate at a specific location – or diffuse pollution – when nutrients from agricultural runoff (when rainwater or irrigation water flows over farmland) end up in rivers. This is particularly relevant in agricultural-dominated catchments.

To mitigate diffuse pollution, solutions span from implementing improved agricultural practices to nutrient and soil management. To address point-source pollution from sewage treatment effluents, nature-based solutions (NBS) and technological approaches at wastewater treatment plant level are preferred. 

The BETA Technological Centre of the UVic-UCC is working on the SEACURE project to tackle nutrient pollution in the soil-river-sea system across the Mediterranean. Researchers are testing several solutions across three Mediterranean countries – Spain, Italy and Greece – all of which are affected by excess nutrient problems. Solutions include prevention, reduction, and remedy of nutrient loss before it reaches the sea.

Tackling Nutrient Loss at the Origin

Precision agriculture and nutrient and soil management can reduce the need for mineral fertilizers, thus preventing nutrient excess inputs into the agricultural systems. Some of these strategies will be used in the SEACURE context in Spain’s central Catalonia, a region with intensive farming and poor management of livestock manure that has led to long-term nitrate pollution. 

Precision agriculture uses nutrients only in areas where they are needed, and the amount of water and pesticides are adapted to each area of the field. This increases productivity and reduces the environmental impacts caused by overfertilization.  

Nutrient and soil management practices include the use of Tailor-Made Fertilisers (TMFs). They are produced from organic livestock waste, and they can help reduce the use of mineral fertilizers. TMFs are formulated according to the specific needs of each crop, and they optimize plant growth and prevent excess nutrients, thereby reducing environmental impact. 

Fertigation is another option. It refers to a system that applies nutrients dissolved in irrigation water, allowing crops to be irrigated and fertilized at the same time. When using nutrient-rich recycled water or organic fertilizers, fertigation can reduce the need for mineral fertilizers and enhance nutrient circularity.

Another practice to enhance soil health is treating soil as a living ecosystem to improve microbial diversity and overall soil health. For example, living soil horticulture involves increasing organic matter content and applying practices such as composts, mulches, cover crops, reduced tillage and other sustainable soil-friendly techniques. Adding wood chips, for instance, increases soil organic matter and improves soil structure, which enhances nutrient retention and nutrient-use efficiency, reducing the need for external inputs. 

Soil health can also be enhanced by implementing cover crops in agriculture. This is based on sowing plants between harvests or between crop rows. In addition to preventing erosion, they increase soil fertility, control weeds, conserve moisture and promote biodiversity in agricultural lands. Cover crops take up and retain nutrients (especially nitrogen) that would otherwise be lost through leaching, runoff, or erosion when the soil is bare.

Finally, perennial crops can also help. They maintain living roots and soil cover throughout the year, can also help reduce erosion and prevent nutrients from being lost through rainwater, runoff, or even wind, since the soil remains protected and structurally stable. Examples include fruit trees, vineyards, olive groves, permanent pastures or innovative perennial cereals.

Reducing the Loss of Nutrients In Rivers

Nature-based solutions can help reduce the input of nutrients from wastewater treatment plant effluents into aquatic systems such as rivers. Phytoremediation, for example, uses natural organisms like microalgae in wastewater treatment processes. This approach reduces nutrient loads at the outlet of wastewater treatment plants while also supporting circular practices through nutrient recovery from the harvested biomass.

Another effective strategy is the creation of artificial wetlands, where water from wastewater treatment plants can be diverted to these artificial ecosystems. Here, organisms (plants, or bacteria) perform a purification function, improving water quality. 

Biological denitrification is being used to tackle diffuse pollution – run-off water from agricultural fields – around the Mar Menor basin in Murcia (Spain). Biological denitrification is a process in which bacteria consume nitrates in the absence of oxygen. Studies have shown that up to 90% of the nitrogen in these waters can be removed. However, the efficiency and scalability of the process still need to be evaluated. 

Remedying Nutrient Loss Before it Reaches the Sea

Within the project SEACURE, solutions will be implemented in river end zones to prevent nutrients from reaching the sea. 

In Italy’s Po Delta, a network of irrigation canals was created at the end of the 18th Century for agricultural use. When full, these canals contribute large quantities of nutrients to the Adriatic Sea. To mitigate this impact, a vegetation strip of the plant Phragmites australis will be introduced. These plants have long roots that enter a symbiotic relationship with denitrifying bacteria capable of reducing the amount of nitrogen. These bacteria have a high capacity to reduce the levels of nutrients transported downstream.

At a wastewater treatment plant located on the Esino River in Italy’s Marche region, a combination of nature-based solutions and technological approaches has been tested. One example is the integration of constructed wetlands with biochar. Produced through the pyrolysis of organic materials such as wastewater treatment sludge or wood, biochar is expected to stimulate microbial activity and enhance nutrient removal.

In the Axios Delta in Greece, floating islets will be constructed and planted with Phragmites australis and other plant species capable of denitrifying the surrounding water. On the Thessaly plain, nature-based solutions like wetlands and ponds with algae will be implemented to clean wastewater. These natural systems can remove pollution and can recover up to 70% of the nitrogen in the water by turning it into algae biomass – which can be reused as, for example, fertilizer.

The Road Ahead

The aim of the SEACURE project is to see if the solutions and results obtained in Mediterranean regions are feasible, and if so, if they are scalable to other areas and countries. The knowledge gathered will facilitate decision-making on holistic nutrient management policies at regional scales. 

Recognizing the profound damage that excess nutrients can cause is only the beginning. From that awareness emerges the pursuit of solutions, which many lay on nature itself. Countless tools are already within reach. Now it is time to move beyond discussion and shape a healthier future for our ecosystems.