Concern about the mass death of fish, the factors that caused it

The revelation images from mass death of fish in the Pagasitiko gulf in Voloscaused intense concern among scientists about the future effects of climate change on the environment and public health.

The effects of storm Daniel it seems that they will continue to trouble the ecosystem and the inhabitants of Thessaly for a long time, after the tons of dead fish in Volos.

And it may be that the management of the problem, by harvesting the fish, incinerating and landfilling them, has been successful, however, the question remains about the ways to deal with similar ecological disasters that cannot be ruled out to increase due to climate change.

The Professor of Environmental Engineering of AUTH, Demosthenes Sarigiannishe explains speaking to iatropedia.gr the root causes that caused this eerie phenomenon and emphasizes that the disaster could have been prevented if preventive measures had been taken.

But what are the main causes that caused this dystopian phenomenon in the Pagasitic Gulf and the images that went around the world?

Mr. Sarigiannis, as Director and Chairman of the Board of Directors. of the National Research Foundation, participated in the competent Committee established for the reconstruction of Thessaly from the environmental disaster. Through his scientific knowledge and experience, he explains in simple terms the 6 problems of ecological imbalance that arose after the bad weather “Daniel” and the burden of Lake Karlas from the carried materials of the flood, which caused the death of fish.

What caused the fish to die?

According to Demosthenes Sarigiannis, the main factors that contributed to the phenomenon are the following:

• Increased food load from transported materials: The flood in Karla and the wider area caused the influx of nutrients-rich materials (phosphorus, carbon, etc.). These favored the growth of microorganisms and fish, creating eutrophication conditions.
• Eutrophication and lack of oxygen: Excessive fish growth, combined with the reduction in water volume from the Carla Lake drainages, led to hypoxia (low oxygen levels in the water), causing fish to suffocate.

“You have less oxygen available for a very large population of fish and as a result the fish develop hypoxia or anoxia – depending on the conditions – and die. Many fish even had an embolism and that’s why they were rising to the surface”, explains Demosthenes Sarigiannis.

• Toxic microorganism blooms: The large increase of micro-organisms, some with toxic properties (toxic blooms), caused further fish deaths, poisoning their environment.
• Temperature rise and evaporation of water: This summer, very high temperatures enhanced water evaporation and reduced oxygen solubility, exacerbating hypoxia.
  Inflow of freshwater fish into the Pagasitikos: After the flood, freshwater fish moved into the Pagasitikos through the Xiria floodplain. Their contact with seawater led to sparging (inflow of salt into their bodies), causing their death. “They were spawned, causing them to burst. You will see in the photos that the fish were “bloated”. The toxic blooms kill the fish, because they poison their environment”, emphasizes the expert.
• Enclosed bay and portable materials: Pagasitikos, as an enclosed bay, did not have the necessary sea turbulence to oxygenate the water sufficiently. The increase in temperatures and the transported materials from the floods also negatively affected saltwater fish, the scientist concludes.

Fish death in Pagasitikos: Could it have been predicted?

Professor Sarigiannis emphasizes that the phenomenon was not unforeseeable, as the factors that caused it were known to the scientific community.

A year ago, the possibility of an ecological imbalance due to the loading of Carla lake by transported materials was highlighted by a written report of the same. At the same time, he had participated in the Scientific Committee for the Reconstruction of Thessaly and had warned about the possible effects on public health and the environment.

“What I had requested in writing was to do a systematic monitoring of the quality of the soil for contamination, and of the water for the development of microorganisms with specific characteristics. We could easily measure all of this. By following the course of the waters all this time, in winter and spring, one could see this situation occurring, for the fish were growing in between. The Dutch company that had undertaken the project I don’t think they did this kind of monitoring and I say it honestly. So in this sense we did not have the required control”, the Professor points out.

How could it be avoided?

The prevention of the phenomenon could have been achieved, according to D. Sarigianni, with the application of the mechanical ventilation method. A method followed in cases where there are indications of low oxygen concentration. By using pumps, enrichment of the water with dissolved oxygen could be achieved.

“If we had found the toxic blooms in time, due to the morphology of the seabed that more fish grow where there is a denser load, we would have detected the oxygen deficit. At this stage we could intervene mechanically and the cost would not be as great as the damage caused afterwards. So if you watch, you can act,” notes the scientist.

It concludes, in fact, that while there is no immediate risk to public health, priority must be given to maintaining the health of the ecosystem. If the ecosystem remains degraded, there could be new crises, especially in the face of climate change, which is intensifying extreme weather events, he says.

“We also had indications of salmonella outbreaks in the area, which is linked to changes in the water table. We are very good at dealing with crisis, but once the crisis is over we quit. This does not characterize resilient societies, this is the truth. And the climate crisis will hit us “on the head” all the time”, concludes the expert.

Source: iatropedia.gr