Spatio-Temporal Assessment of Surface Water Quality Using the Water Quality Index: Insights from the Marchica Lagoon, Morocco
This study evaluates the spatial and seasonal water quality of Morocco's protected Marchica Lagoon using the Water Quality Index, revealing significant degradation in areas near pollution sources like Oued Caballo and Oued Selouane due to untreated wastewater and agricultural runoff, while highlighting the need for integrated watershed management to ensure the lagoon's ecological sustainability.
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Water is rarely just water. In the natural world, it is a moving mixture of minerals, living things, and the waste of human activity. When scientists study a body of water like a coastal lagoon, they do not just look at how clear it is. They measure a long list of chemical ingredients to understand what is happening beneath the surface. Some of these ingredients, like nutrients from fertilizer or sewage, can feed tiny plants called algae. If there are too many of these nutrients, the algae grow out of control, using up the oxygen that fish and other animals need to breathe. This process, known as eutrophication, can turn a healthy ecosystem into a dead zone. To make sense of dozens of different chemical measurements, researchers often use a tool called a Water Quality Index. This index acts like a single report card, combining all the complex data into one number that tells you if the water is safe for drinking, safe for watering crops, or in need of serious help.
In the northeastern corner of Morocco, a large coastal lagoon known as Marchica sits between the Mediterranean Sea and the African continent. It is a place of great beauty and importance, recognized internationally for its wildlife and protected by treaty. However, like many places where land meets sea, it faces heavy pressure from the people living nearby. The lagoon receives water from rivers that drain the surrounding land, carrying with them runoff from farms, cities, and industries. To understand the true state of this vital ecosystem, a team of researchers set out to map the water quality across the entire lagoon, looking at how it changes from season to season and from one spot to another. They wanted to know if the water could still support life and if it was safe for the local communities to use.
The researchers chose sixteen different spots to take water samples, spreading them across four main areas of the lagoon. These areas included the mouths of two rivers, the Caballo and Selouane, which flow into the lagoon, as well as two other zones closer to the open sea and the center of the water body. They collected water four times a year, capturing the conditions during autumn, winter, spring, and summer. At each location, they measured seven key things: how salty the water was, how much oxygen was dissolved in it, how much organic waste was present, and the levels of nutrients like nitrogen and phosphorus. They then fed these numbers into a calculation that compared the results against strict Moroccan standards for drinking water and irrigation.
The results painted a picture of a lagoon under significant stress. The water quality was not the same everywhere; it varied sharply depending on where you looked. The areas closest to the river mouths, particularly where the Caballo and Selouane rivers enter the lagoon, showed the worst conditions. In these spots, the water quality index scores were so high that the water was deemed completely unsuitable for drinking without advanced treatment. Even for farming, the water was classified as very poor, meaning it would require treatment before it could be used to irrigate crops. The high scores in these areas were driven by large amounts of untreated sewage, industrial waste, and fertilizer runoff from the nearby land. The water here was rich in nutrients and organic matter, a combination that creates a high risk of oxygen depletion and algal blooms.
In contrast, the water near the center of the lagoon and closer to the artificial channel connecting it to the sea was in much better shape. This area, known as Kariat Arkmane, showed significantly lower pollution levels. The researchers found that the constant mixing with the sea water helped to dilute the pollutants and keep the water fresher. The area known as Beni Enssar fell somewhere in the middle, showing signs of pollution from the nearby city but also benefiting from the exchange with the ocean. The study confirmed that the degradation of the water was not a uniform problem but was concentrated in specific hotspots where human activity was most intense.
To understand the root causes of this pollution, the researchers used a statistical method to group the different chemical measurements together. They discovered that the levels of ammonium, total phosphorus, and organic waste moved in lockstep. When one went up, the others went up too. This strong connection suggested that these pollutants were coming from the same sources: untreated domestic wastewater and agricultural runoff. The data showed that the nutrients were not just floating around randomly but were being delivered together in pulses from the land. The study also found that the water in the lagoon was highly mineralized, with electrical conductivity readings ranging from 3,200 to 9,860 microsiemens per centimeter, indicating a high concentration of dissolved salts, likely from seawater intrusion and evaporation.
The researchers concluded that the lagoon is suffering from a combination of organic pollution, nutrient overload, and suspended solids. While the water near the sea inlet remains relatively healthy, the inner parts of the lagoon are struggling to cope with the volume of waste entering from the rivers. The study highlights that without changes, the risk of eutrophication remains high, threatening the fish, the plants, and the overall health of the ecosystem. The authors suggest that the solution lies in better management of the entire watershed. This means upgrading wastewater treatment plants, controlling how fertilizers are used on nearby farms, and creating buffer zones to catch runoff before it reaches the water. They emphasize that continuous monitoring is essential to track these changes and to ensure that the lagoon can continue to support both the wildlife it protects and the people who depend on it. The work serves as a clear warning that the health of the lagoon is directly tied to how the land around it is managed.
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