Translated by Jennifer Castner
Research by Ukrainian scientists into the impact of the Kakhovka hydropower plant dam’s destruction on life in the Black Sea reveals unexpected results.
On 6 June 2022, Russian occupation forces launched a terrorist attack, blowing up the Kakhovka hydropower plant’s dam. Almost 140 km2 of land was flooded with water. Households, cesspools, landfills, sewage drains, warehouses with agricultural chemicals, car engines, and the generating units of the hydropower station itself, gas stations, and bottom sediments in the Kakhovka Reservoir – all was washed away by the floodwaters, ultimately ending up in the Black Sea.
Director of the Ukrainian Scientific Center for Marine Ecology (UkrNCEM) Viktor Komorin reported that the center’s staff analyzed water samples and discovered colossal pollution of the Black Sea following the disaster. Their analysis showed much higher than typical levels of heavy metals such as copper and zinc. The samples also contained arsenic and toxic and carcinogenic chlorine compounds. A little over a month ago, Komorin noted that water quality had since improved, but the toxins had not dissolved, instead accumulating on the Black Sea’s seafloor. The lower reaches of the Dnieper remain a pollution hot spot.
Blooms began and ended
Immediately after the disaster, the forecasts were dire. In addition to the temporary reduction in salinity of the Black Sea that actually occurred for a short period (by early July the seawater salinity had normalized, albeit at a minimum level of 12-13 ppm), scientists predicted that all the pollutants that had entered the Black Sea along with that mass of water would affect all categories of living organisms – from plankton to cetaceans. Combined with hot summer conditions, a large volume of polluted freshwater could provoke the widespread growth of microorganisms and algae and stimulate algal blooms and all its associated negative consequences.
These predictions came to be. In July, over 1,500 km² of seawaters near Odesa were overgrown with dangerous and toxic blue-green algae. And, although water bloom is an annual phenomenon, in this instance, it was many times greater than in the previous year.
According to Galina Minicheva, director of Ukraine’s Marine Biology Institute (National Academy of Sciences) and corresponding member of the National Academy of Sciences of Ukraine, it is this algal bloom that will be the factor to finally clear the sea of some pollutants:
“The processes of absorption, transformation, and deposition of substances can now only occur in the seabed. This will be facilitated, oddly enough, by the algal bloom that has already begun, she explained less than two weeks after the disaster. And the more intensively it progresses, the more and faster algae will take up the organic substrate on which bacteria, including pathogenic ones, feed. In this situation, one must be patient and be grateful to the sea for the fact that it will bear most of the terrible consequences of this immoral catastrophe”.
Bioluminescent phytoplankton (left) seen from space in summer 2022. Source: Sentinel-3 OLCI enhanced True Color RGB and (right) close view. Source: DW. In total, roughly 150 different species of phytoplankton were counted in the Black Sea.
According to marine biologist and Marine Biology Institute (Ukrainian Academy of Sciences) director and corresponding UAS member Maria Pavlovska, the bloom has already ended, and this process was to be expected.
“There has been massive growth of phytoplankton due to organic pollution. When phytoplankton dies and decomposes, oxygen levels in water drop, a very bad thing for all marine life that depends on it. That said, we can now state that all organic matter has been processed, the bloom is over and no longer present”, she said.
Dolphins are again dying
According to the Ukrainian Scientific Center of Ecology of the Sea (UkrSCES), dolphins began to die again after the explosion at the Kakhovka hydropower plant in the Black Sea. The center explained that during spring and summer 2022, cetacean mortality (porpoise and common dolphin) increased in the Black Sea, particularly in the western Black Sea. There were no such phenomena in 2023 until in June and July 2023, when several cetaceans were found dead on the shores of the Odesa region – in Odesa itself and south of the city.
Two dead porpoises were examined and samples collected in an attempt to detect a potential connection between the Kakhovka disaster and cetacean deaths.
The autopsy was carried out by Karina Vishnyakova and Pavel Goldin, Doctor of Biological Sciences of the Schmalhausen Institute of Zoology (Ukraine National Academy of Sciences). According to Goldin, a large number of atypical pollutants, bacteria, and pathogens entered the sea after the water was released from Kakhovka reservoir, all of which could potentially harm dolphins.
Scientists seek the true cause of porpoise deaths
After examining the dolphins’ bodies, the scientists eliminated most scenarios for these cetacean deaths and are studying samples to rule out poison or infectious disease. The last two options could be linked to military operations in the Black Sea and/or sea pollution related to the Kakhovka disaster.
“Although both bodies were severely decomposed, the autopsy made it possible to rule out death caused by fishing gear, fungal infections, injuries and wounds, broken bones, or signs of internal injuries”, noted the autopsy report. Consequently, scientists wondered if these deaths could be the result of an infectious disease or acute/chronic poisoning; could they have occurred as a result of Russian military operations, or the explosion of the Kakhovka hydropower plant dam?
Just two weeks after the Kakhovka disaster, four dead dolphins were found on the shores of Odesa and Kherson oblasts. After an autopsy, fish and seeds were found in the stomach of one of the porpoises, neither of which dolphins ever eat. Now a group of scientists are working like criminologists step by step to figure out what the porpoise did in the last days of its life.
“The working hypothesis is that some fish ate the seeds, and a dolphin ate that fish. Dr. Galina Pashkevich, a well-known Ukrainian archaeobotany scholar, analyzed the data and reached specific conclusions: these seeds are typical of upland plants with no connection to the Black Sea. Genetic and morphological analyses to determine the type of fish found in the animal’s stomach are ongoing. However, we can tentatively say that some of these were freshwater fish, meaning they came from the lower Dnieper”, said Pavel Goldin.
Thus, the true cause of the dolphin’s death remains to be discovered. After each autopsy, Ukraine sends samples to experts at the University of Padua in Italy and the University of Hannover in Germany for additional analyses. Some tests are also being carried out in Ukraine, the results of which have not yet been officially announced.
Tasked by the Prosecutor General’s Office, the Marine Biology Institute (National Academy of Sciences of Ukraine) is conducting research near Odesa Bay. The results have yet to be finalized, but intermediate observations can be made.
According to Schmalhausen Institute of Zoology’s Pavel Goldin, 31 dead dolphins have been found stranded in Ukraine (as of 4 September), including Crimea, in 2023. As of the same time last year, 110 dead dolphins had been discovered.
Numbers in 2022 and 2023 were compared to the average over 2018-2021. In 2023, significantly fewer dolphins were stranded than the average. In contrast, in 2022 many more dolphins were stranded relative to the same 2018-2021 period.
“We don’t yet understand the reason for this. We will observe and draw conclusions later,” said Goldin.
Struggle for a “place in the sun” in the sea, or in our case, for a “place at the bottom.”
Due to the facts that, following the Kakhovka disaster the wind seemed to push freshwater against the Black Sea coastline and the breakwaters did not allow it to move away, the flooding freshwater remained near the coastline for about ten days.
Mussels, of which there have always been many on the Odesa coastline, are tied to places with periodic desalination, and they exist at river mouths. The minimum salinity required for mussels is five ppm. If conditions become completely uncomfortable, they can close their valves and wait up to a week and a half in this isolated state. If water freshens briefly, the mussels survive, but if it stretches past their ability to cope, they die.
Something in between occurred after the Kakhovka disaster, explained Aleksandr Kurakin, a dive specialist at the Marine Biology Institute.
Not all the mussels died, but older specimens did not survive the tragic events. The young ones were practically unharmed. At sea there is always a struggle ‘for a place in the sun,’ or in our case, for a place at the bottom. Now, young mussels have already settled and are growing in places where the old mussels died, explained the scientist.
Eating mussels is nevertheless prohibited for the time being, given the organisms’ fantastic ability to absorb everything that gets into the water. To avoid increasing the concentration of heavy metals in the body, it is better to avoid mussels, rapa whelk, and fish in general from the Black Sea.
Fish stuck around while crab numbers grow
When the Black Sea’s salinity fell, there was a risk of death for marine fish not adapted to survive in freshwater. This was mentioned immediately following the Kakhovka disaster, and there is encouraging news.
Kurakin explained that from time to time the river and sea currents transport freshwater from the Dnieper-Bug Estuary into Odesa Bay, covering the upper layer of the water column by about 3-4 meters. In response, fish dive into the depths, and the crabs crawl away.
There was no goby fish dieoff. Some fish died, but not tens or hundreds of thousands of dead fish, said the scientist.
There was a time in the 1970s and 1990s when crabs almost disappeared from Odesa Bay. Enormous crab dieoffs occurred due to large volumes of river pollution draining into an area stretching from Crimea to the Danube Delta. The ingress of sewage, agricultural fertilizers, and other waste led to strong algal blooms in the water, which, in turn, reduced water oxygenation and caused dieoffs.
Such dieoffs occurred several times a year. It is difficult to imagine how the sea survived this, but it demonstrates the ecosystem’s resilience as well as the ability of its organisms to survive. If it weren’t for the sea’s crazy driving force, it would have been gone a long time ago. Over the millions of years of its existence, the sea has survived a lot, and, of course, it will survive the Kakhovka catastrophe, says Kurakin.
This thesis is playing out right now, as humans witness the Black Sea’s self-restoration. Kurakin noted that the marble crab (Pachygrapsus marmoratus) population, which had almost entirely disappeared 30 years ago, is on the rebound: “Diving into the water after the Kakhovka hydropower plant dam explosion, we first encountered tiny marbled crabs in very large numbers. With each new dive, we encountered more and more of them.”
The sea’s recovery
Currently the Black Sea is experiencing heavy anthropogenic pressure from military operations. Fuel, oil products, and noise pollution enter the sea, and marine mammals are vulnerable to echolocation injuries. However, Maria Pavlovska commented that scientists were seeing signs of the Black Sea’s recovery following the Kakhovka disaster.
At the time of the flood, a very large quantity of organic and chemical substances, including toxic substances, entered the Black Sea and settled on the seabed. However, as noted earlier regarding organic substances, those have largely dissolved.
The situation is different for mercury and heavy metals, given their ability to accumulate in marine organisms. According to Pavlovska, exact figures for their concentration in the sea are not known, because scientists are unable to conduct large-scale studies including the catch of different biota.
“We are sampling now, but this is not the level of monitoring that is needed,” Pavlovska said. “We will conduct a comprehensive study after the hostilities end.”
In conclusion, Maria Pavlovska said that the Black Sea remains capable of “digesting” everything that enters as a result of the Kakhovka disaster, although it will take much longer to process harmful substances.
It is also worth remembering that pollution of the Black Sea is associated not only with military actions, but also with the pollution of rivers flowing into the sea – i.e., the Dnieper and Danube. Over the past 20 years, a number of UNDP Global Environment Facility-funded projects to protect international waters in the Danube and Black Sea basins have resulted in legal, legislative, and institutional reforms, and have also identified 500 priority investments to prevent water pollution. This, in turn, created a welcoming environment that has attracted over USD $3 billion of investments in reducing nutrient pollution from 17 countries located in those rivers’ basins.
These investments helped reduce the load of nitrogen and phosphorus entering the Black Sea by 25 by 25,000 and 4,000 metric tons per year, respectively. These reductions have reversed expansion of the hypoxic zone on the northwestern Black Sea shelf, achieving significant progress in restoration of the shelf ecosystem. However, work remains to be done, and prospects for the development of legal environmental standards are significant.
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