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EUTROPHICATION IN THE BLACK SEA
From L. Mee, “How to save the Black Sea, Your Guide to the Black Sea Strategic Action Plan”, 2000
. Summary: The most significant process degrading the Black Sea has been the massive over-fertilization of the sea by compounds of nitrogen and phosphorus, largely as a result of agricultural, domestic and industrial sources. This over-fertilization produces a phenomenon called eutrophication which has changed the structure of the Black Sea ecosystem. The nitrogen and phosphorus compounds (termed as nutrients ) enter the Black Sea from sources from the 17 countries in its drainage basin, particularly through rivers. It is estimated that the six Black Sea countries contribute about 70% of the total amount of the substances flowing to the Black Sea as waste from human activities. Some of this amount and almost all of the remaining 30% (from the other eleven non-coastal countries) enter the Sea via the Danube River.
Eutrophication means the over-enrichment of water bodies with organic matter. The most important source of organic matter in the sea are the tiny floating plants which grow in all surface waters where there is enough light and essential nutrients, particularly the nitrogen and phosphorus compounds upon which all plant life depends. These tiny plants are called phytoplankton and there are thousands of species of such plants, each with specific requirements for light, temperature, nitrogen, phosphorus and complex combinations of other essential nutrients such as iron and vitamins. Some phytoplankton species, known as diatoms have glass-like shells and have an additional requirement for dissolved silica. In the sea, different plant species bloom when the conditions for them are right, and later fade to be replaced by other species in much the same way as flowers and grasses in a meadow. They are often grazed, eaten by tiny marine animals known zooplankton. These in turn are consumed by larger animals in a food chain which often ends with fish or mammals such as dolphins, seal and humans. Almost all animals in the sea share a common requirement for oxygen. Enough oxygen dissolves in seawater to sustain marine animals, except for mammals and some reptiles, which come to the sea’s surface for air.
In shallow areas of the sea, where the seabed is bathed in light, larger plants and algae may grow in underwater meadows. These too can form the base of a food chain but also provide shelter for a myriad of animals which live attached to the sea floor or arrive as visitors, sometimes remaining during an important stage in their reproductive cycle. The North-western part of the Black Sea is largely below one hundred meters deep and always received a good supply of nutrients from the rivers Danube and Dnipro, Europe’s second and third largest rivers. It was virtually covered with underwater meadows. One species alone, a red algae called Phyllophora, dominated an area with the combined size of Belgium and the Netherlands. The meadow, named Zernov’s field after its Russian discoverer, was the home to a unique and highly productive ecosystem of plants and animals. Incidentally the red algae were also harvested by humans for their agar, used as an ingredient for ice cream.
Sadly the above text uses the word “was”. During the 1970s and 1980s, the NW Shelf ecosystem rather suddenly and catastrophically collapsed. Vast amounts of dead plants and animals covered the beaches of Romania and western Ukraine; between 1973 and 1990, losses were estimated as 60 million tons of bottom animals including 5 million tons of fish.
Why did this occur? The catastrophe appears to have been a consequence of eutrophication. During the late 1960s, there was a major change in agricultural production often called the “green revolution”. This involved the use of large amounts of fertilizers and pesticides to sustain high crop yields. Intensive animal farms were also established to provide a cheaper source of meat (one farm in Romania, for example, had more than a million pigs). Discharges of waste nutrients from these agricultural activities, and from domestic and industrial sources across the Black Sea basin, entered rivers and streams and eventually found their way to the Black Sea itself. The seagrass and algal beds of the north-western shelf were unable to absorb such large amounts of nutrients and large quantities of phytoplankton began to grow, shading the light from the larger plants below. Deprived of light, the meadows began to die. The huge amount of additional decaying organic matter at the sea floor, and associated bacteria, used up the dissolved oxygen resulting in a dead-zone where all the bottom dwelling fauna was asphyxiated.
The effects of eutrophication were felt across the entire Black Sea. Though it is estimated that 70% of the dissolved nutrients produced by human activity came from the Danube River alone, there are no innocent countries and coastal eutrophication is observed in areas well away from the influence of the Danube. Indeed, the whole sea suffered changes in the structures of its ecosystem during the last three decades and eutrophication is one of the factors which has contributed to this change. Organisms which are specialized in feeding on surplus organic matter have appeared in large numbers all around the Black Sea coast but these are often regarded as “dead end” species as they do not serve as fodder for zooplankton and the rest of the food chain. In many respects, the “fertilization“ of the sea with nutrients has made it poorer and not richer.
The nitrogen and phosphorus compounds triggering eutrophication come from all over the Black Sea Basin, a huge area of Europe spanning parts of seventeen countries and including about 160 million people. A study by the Black Sea Environmental Programme suggests that, in 1992, 70% of the nutrients were coming from the six Black Sea countries (three of which – Romania, Bulgaria and Ukraine – discharge much of their nutrient load through the Danube) and the remaining 30% comes from the non-coastal countries, mostly of the upper Danube. Studies by the Danube Basin Environmental Programme suggest that about half the nutrients discharged to the river are from agriculture, one quarter from industry and a similar proportion form domestic sources. The current loads of nutrients entering the Black Sea from the Danube has fallen in recent years due to the collapse of the economies of most lower Danubian and former Soviet countries, the measures taken to reduce nutrient discharge in the upper Danube countries, and the implementation of a ban in polyphosphate detergents in some countries. Current phosphate levels appear to be roughly the same as in the 1960s but total nitrogen levels are still at least four times as those observed during that period. There is evidence of some recovery in Black Sea ecosystems but this remains limited. It is widely considered that nutrient discharges are likely to rise again, with consequent damage to the Black Sea, unless action is taken to implement nutrient discharge control measures as part of the economic development strategies.
Much money and energy is used to manufacture the fertilizers applied in agriculture. The loss of thee substances to rivers and the sea is an economic loss for agricultural production. It is also the cause of serious environmental problem and damage caused costs large sums of money to repair. Methods are available to economize on fertilizer use and improve land use and waste treatment in order to reduce these losses. Restoration of natural wetlands, efficient in nutrient removal , is another way to improve the situation with the added benefit of providing a habitat for wildlife and protection against flooding.
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