The cause of the appearance of toxic algae in the lakes of America

The waters of Lake Erie and other Great Lakes of America are almost every year covered with algae and become poisonous to humans due to changes in the phosphorus cycle provoked by agriculture.

“Phosphorus fertilizers today are a guarantee that mankind can provide itself with the volume of food that is necessary for us to survive.On the other hand, we know almost nothing about how long this phosphorus remains in the lakes, after its” washed away “by rains from the fields,” says Jason Venkiteswaran of Wilfrid Laurier University in Waterloo, Canada.

Flowering of water is caused by brown or blue-green algae, living both in fresh lakes and reservoirs, and in sea water. With the explosive growth of the amount of cyanobacteria and brown algae in the water, there are large spots that can pose a threat to the health of people and animals due to the toxins that algae release into the water, clearing their “living space”.

It is believed that climate change and, in particular, the rise in water temperature, will contribute to the increase in the incidence of algal blooms and increase in the size of spots, but all the climatic consequences from their occurrence are as yet unknown.

Venkiteswaran and his colleagues have discovered another major factor governing the flowering of plankton and how long they will poison the freshwater and marine water bodies of the Earth, trying to understand what makes Erie Lake and many other Great Lakes of North America covered with giant algae spots almost every year.

As scientists explain, the main limiting factor of algae growth in temperate and tropical latitudes is usually not the water temperature or the number of sunny days, but how much nitrogen and phosphorus is contained in the water of a lake, river or ocean. If one nutrient is plentiful and the other is small, algae will begin to fight each other for a “scarce” resource, releasing toxins.

The main source of “excess” phosphorus and nitrogen is a person using a huge number of compounds of these substances to fertilize fields. A significant part of these nutrients does not remain in the water, but settles on the bottom of lakes and rivers, and scientists have long wondered whether they remain there for good or are gradually seeping into the water.

After studying samples of water and soil from the bottom of about 70 different lakes in Canada, the authors found that the “leaks” of phosphorus occur almost everywhere, and that this process can take place very quickly, and very slowly. For example, phosphorus quickly disappears from small steppe lakes in the north and east of the continent, and very slowly – from the Great Lakes.

This may explain why all measures protecting lakes and rivers from getting there drains from the fields, while almost do not affect the flowering of algae in Lake Erie and his “cousins” – on their bottom a huge amount of phosphorus accumulates, which will slowly emerge in their water for the next decades. This will significantly complicate the fight against the poisoning of lake waters in the future, scientists conclude.