A new scientific study has shown that the construction of dams on the streams of valleys and rivers in the countries of the southern bank of the Mediterranean leads to the deterioration of biodiversity and an increase in salinity in coastal lakes of great economic and environmental importance.
According to the study conducted on the coastal lake of Bizerte, north of Tunisia, the lack of water flow to it due to the construction of dams and climatic changes led to a remarkable increase in salinity and caused great damage to its biodiversity with the emergence of invasive organisms that did not exist before.
The researchers called for the need to work urgently to protect the lake, which plays a pivotal role in the ecological balance in northern Tunisia, as well as its important economic role.
The team that carried out the study included researchers from the National Institute of Marine Science and Technology at the University of Carthage, the Faculty of Science at the University of Tunis El Manar, and the University of Southern California.
Lake Bizerte location on the map (Google Maps)
Environments sensitive to changes
Lake Bizerte is one of the most important lakes in northern Tunisia.
Its area is estimated at about 15,000 hectares (more than 37,000 acres) and the water depth in it reaches about 12 meters.
It is connected to the sea through a channel with a width of 300 meters and a length of 7 kilometers, into which a significant number of streams and valleys flow, in addition to a channel linking it to Lake Ichkeul, which has a unique ecosystem.
Previous scientific studies, some of which date back more than a century, have shown that the coastal Lake of Bizerte had an important biodiversity in the past.
But it seems that this is no longer the case during the past few decades, according to the study recently published in the scientific journal "Marine Pollution Bulletin".
Dr. Ola El-Amrouni, a researcher at the National Institute for Marine Science and Technology, says that the study was "completed within the framework of the Modapex research project, which is supervised by the institute to study pollution in the lakes of Bizerte, Ichkell and the Tinja Canal linking them." "We periodically conduct modeling studies of water movement and biodiversity in these systems."
According to the study, coastal wetlands, which include coastal lakes, ponds, and sabkhas in arid and semi-arid regions, are sensitive natural environments, and changes that occur in climatic, water and sedimentary factors affect the ecological balance in them.
"A lot of dams are currently being built to confront the problem of water scarcity in the countries of the Mediterranean, especially in the countries of the southern bank of it, which affects these ecosystems. Therefore, we wanted to know whether the dams had an impact on the coastal lake of Bizerte or not," she says. Dr. Nadia Kaaloul, a researcher at the Faculty of Science in Tunis and the lead author of the study, gave an exclusive interview to Al Jazeera Net.
A member of the research team taking samples from the water and soil of the lake (National Institute of Marine Science and Technology)
Saltier water than the sea and gaseous organisms
To understand the changes that occurred over the past decades in the salinity, sedimentary soil composition and biodiversity in the coastal Lake of Bizerte, researchers in 2016 took water and sediment samples from more than 20 sites from the lake to study the salinity and microorganisms that colonized it over time.
These organisms represent "biological indicators to determine the changes in the salinity of the lake and the temperature prevailing in it over time, as well as the quality of the biosphere in it," says Al-Amrouni.
The results of sedimentary samples analysis, according to Qaaloul, showed the presence of 39 species of microscopic organisms known as "foraminifera", distributed unevenly throughout the lake.
These organisms, which have a microscopic shell cover, are considered protocells, appearing more than 500 million years ago, and are sensitive to salinity changes in the areas in which they live.
Although previous studies confirm the presence of great biological diversity in the lake, the researchers were surprised by the total absence of these microscopic single-celled organisms west of the lake at the mouth of the Tingeh Canal, one of the most important sources of fresh water reaching it from the neighboring Lake Ichkeul.
They also found, for the first time in the region, invasive microorganisms that are usually known to exist in hot regions.
To further understand the causes of these major biological changes in the lake, the researchers studied the evolution of salinity in the lake, and returned to the results of regular measurements made over the past 25 years.
The team found that the salinity of the lake’s surface water in the west of the lake at the mouth of the Tineh Canal was about 40 grams per liter, compared to only 35.4 grams per liter in 2004, “which means that it has become more salty than the sea,” says Qaaloul.
Microscopic organisms became extinct from the increased salinity of the lake (National Institute of Marine Science and Technology)
Construction of dams and climate change in the accusation circle
The researchers concluded that this higher salinity prompted the local microorganisms to migrate toward the valley estuaries, where the salinity should have been lower.
But the decline in the flow of these tributaries with fresh water and sandy soil as a result of the construction of dams led to their extinction.
The authors pointed out that the cessation of feeding the lake with sandy soil due to the establishment of dams, in turn, contributed to major changes in the biological system inside the lake.
"The soil has turned into clay in some areas, and it tends to retain pollutants and heavy metals with a lack of oxygen," according to the researcher Al-Amrouni.
The researchers also concluded that these changes are also associated with climatic changes and rising water temperatures with reduced precipitation, which led to the invasion of tropical microorganisms in the lake.
However, the construction of dams on the streams of valleys that drain into coastal lakes remains more influential in the deterioration of their biodiversity.
Dr. Issam Hajji, a researcher at the University of Southern California, and one of the contributors to the study’s completion, said in an exclusive interview with Al Jazeera Net via social media, “What we want to say in the study is that the construction of dams is not without damage, as it deprives the lake of water and a certain quality of water. soil, which harms its biodiversity.
Should dams be abandoned in arid regions to preserve biodiversity in coastal lakes?
(Bq)
Should dams be abandoned?
The results of this study confirm what researchers have found in previous studies conducted on other coastal lakes in the countries of the southern bank of the Mediterranean, such as those located near the Nile Delta in northern Egypt.
These lakes witnessed a deterioration in their vital systems and an increase in their salinity due to the decline in water flows to them with the appearance of invasive organisms similar to those found in Lake Bizerte.
"We want to create awareness among citizens and decision-makers about the state of these lakes and the importance of preserving biodiversity in them," Hajji added. But should dams be abandoned to preserve biodiversity in coastal lakes?
The answer is absolutely no, according to the Egyptian scientist. "Building dams means saving water, but biodiversity means agriculture and fisheries, and thus providing food. We do not have to choose between water and food, but rather a balance must be found between them, and we must not solve one problem at the expense of another."
The Egyptian scientist stressed that other lakes in the North African region, such as the coastal lakes in the Nile Delta, were affected by these same factors, calling on officials in the region to confront these problems “on one side,” as he says, stressing that cooperation in the field of scientific research will help in exchanging experiences. and research results of the countries of the region.