Scientists have uncovered the secret of the appearance of toxic algae in the lakes of America

© Photo : NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological SurveyЦветение of algae in American lake ErieScientists have uncovered the secret of the appearance of toxic algae in the lakes of America© Photo : NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey

The waters of lake Erie and other Great lakes of America almost every year covered with algae and become toxic to humans due to changes in the cycle of phosphorus provoked by agriculture, according to a paper published in Canadian Journal of Fisheries and Aquatic Sciences.

«Phosphate fertilizers today are to ensure that humanity can provide itself the amount of food we need for survival. On the other hand, we know almost nothing about how long this phosphorus remains in the lake after him to «wash away» the rain from the fields,» says Jason Venkiteswaran (Jason Venkiteswaran) from Wilfrid Laurier University in Waterloo (Canada).

Algal blooms cause brown or blue-green algae that live in freshwater lakes and reservoirs and sea water. With the explosive growth in the number of cyanobacteria and brown algae in the water occur extensive spots that may pose a threat to human health and animals because of the toxins that the algae produce water, clearing his «living space».

It is believed that climate change and, in particular, rising temperatures will contribute to more frequent cases of algal blooms and increase the size of the spots, however, all climate impacts from their occurrence are still unknown.

Venkiteswaran and his colleagues discovered one more main factor controlling plankton blooms and how long they will poison the freshwater and marine water bodies of the Earth, trying to understand what makes lake Erie and many other Great lakes of North America covered with giant spots of algae almost every year.

As the scientists explain, the main factor limiting growth of algae in temperate and tropical latitudes are usually not water temperature or number of Sunny days, but how much of the nitrogen and phosphorus contained in the water of a lake, river or ocean. If one nutrient is a lot and the other not enough, then algae will start to fight each other for «scarce» resource, releasing toxins.

The main source of the «extra» phosphorus and nitrogen is of a man using a huge number of compounds of these substances for fertilizing fields. A significant portion of these nutrients do not remain in the water and settles to the bottom of lakes and rivers, and scientists have long been interested in whether they remain there forever or gradually seep into the water.

After examining samples of water and soil from the bottom of the about 70 different lakes in Canada, the authors found that «leakage» of phosphorus occurs almost everywhere, and that this process can go very quickly or very slowly. For example, phosphorus is rapidly disappearing from the small steppe lakes to the North and East of the continent, and very slowly – from the Great lakes.

This may explain why all measures that protect lakes and rivers from getting runoff from the fields, while almost no effect on the algae bloom in lake Erie and its «cousins» – on their day there is a great amount of phosphorus, which will slowly stand out in their water for decades to come. This will significantly complicate the fight against the poisoning of the waters of the lakes in the future, the scientists conclude.

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