Danube so blue, so beautiful and blue, through the valley and the field moves down , the choirs sing in the waltz that Johann Strauss Jr. first premiered on February 13, 1867 . At that time, without a doubt, the Danube River looked so beautiful and clean as to inspire what is unofficially considered to be the second Austrian anthem. But today the colors that the second longest river in Europe shows us evoke a very different mental image , which relegates that “ so beautiful and blue ” Danube to a 155-year-old frame of melancholy and nostalgia.
Intensive industrialization, as well as equally intensive agricultural and livestock activities along the course of this iconic river, as has happened with many other rivers in Europe, has resulted in an increase in pollutants in its waters . Over the last century and a half, the Danube has received raw sewage, especially as it passes through large cities such as Vienna, Bratislava, Belgrade or Budapest . Other European cities have also made their polluting contribution to the Danube from its tributaries, such as the city of Sofia from the Isker River, or Bucharest from the Dâmbovița, through the Arges River.
Among the industrial waste that, mainly during the 20th century, has been dumped into the waters of the great river, heavy metals such as cadmium, lead, or iron stand out . These pollutants enter the food chains of ecosystems, and accumulate in the tissues of the animals that live in their waters. And so much so, that the analyzes carried out on these animals show levels of heavy metals that exceed the maximum concentration that the European Union considers as “acceptable” for consumption. That is, they accumulate so many contaminants that they cannot even be eaten. These high concentrations of heavy metals also present what we call genotoxicity , that is, they cause damage to the genetic material .
But not only industrial waste is responsible. In many of the places that the great Danube River flows through, there is not even a system for processing domestic wastewater . What goes down house drains ends up, in many cases, in the same river as livestock and agricultural waste, increasing the amount of decomposing organic matter and inorganic nutrients —such as phosphates and nitrates—, and altering thus aquatic ecosystems . An effect is produced that we call “ eutrophication ”, which is colloquially known as “ the green soup ”.
In this process, the abundant nutrients favor the proliferation of algae that cloud the water and prevent sunlight from reaching the deepest parts. There, the plants stop photosynthesizing, die, and decompose . At the bottom, oxygen is exhausted, and the ecosystem as a whole becomes inhospitable to the animals that once lived there . In the case of rivers in general, as they are masses of water that move and renew, these effects are more diluted than in lagoons and other wetlands. But at some times of the year, eutrophication is a serious problem for the Danube , especially in the lower reaches, where the currents are much slower.
However, there is something else that, especially in recent decades, has turned the Danube into a polychromatic canvas . It’s about the plastic. It is estimated that the great river supplies the Black Sea with more than four tons of plastics every day. Once again it is the industries that are contributing the most to this new problem; Almost 80% of the plastics that pass through it have an industrial origin. To such an extent this can be a problem, that at times there have been more plastic particles in the Danube waters than fish fry .
Danube so blue, so beautiful and blue, Through the valley and the field moves down , the choirs sang in Strauss’s waltz. How was he to know that, a century and a half after producing his greatest work, that beautiful blue would be faded by heavy metals, greenish by eutrophication and faded by plastics ?
A contamination that humanity has been throwing out, and that through the valley and the countryside moves downwards .
REFERENCES
Kiss, K. T. 1994. Trophic level and eutrophication of the River Danube in Hungary. SIL Proceedings, 1922-2010, 25(3), 1688-1691. DOI: 10.1080/03680770.1992.11900469
Lechner, A., Keckeis, H., et al. 2014. The Danube so colourful: A potpourri of plastic litter outnumbers fish larvae in Europe’s second largest river. Environmental Pollution, 188, 177-181. DOI: 10.1016/j.envpol.2014.02.006
Sunjog, K., Gačić, Z., et al. 2012. Heavy Metal Accumulation and the Genotoxicity in Barbel (Barbus barbus) as Indicators of the Danube River Pollution. The Scientific World Journal, 2012, e351074. DOI: 10.1100/2012/351074
