Algae plague in the lake

If over-fertilization causes algae to proliferate, all you have to do is remove them. Then other aquatic plants grow stronger and lead to clear water. This was thought for a long time, but turned out to be wrong.

Alternative Equilibria

Shallow lakes have long been considered the prime example of alternative equilibrium theory. According to this, a lake can go through very different stages, but once it has clear water with a lot of vegetation, then it stays that way. The same would apply to bodies of water showing turbid water and heavy algae growth. Each of these alternate states should be fairly stable.

Excessive algae formation

Especially in the summer months, an explosive proliferation of algae, the so-called algal bloom, can occur in ponds. Algae do produce oxygen, but when they die, they start to rot and decompose. So much oxygen is used up again that fish die from it.

Consequences for algae control

If one follows the theory of alternative equilibria, then it should be relatively easy to permanently transform an algae-infested shallow water lake into a biotope with clear water. One removes the algae and takes care of aquatic plants. This would have brought the body of water from a state of equilibrium to an alternative one that should be stable over the long term.

error cleared up

The researchers looked at more than 900 lakes, especially phosphorus and nitrogen, which we know from the fertilizer and of course the chlorophyll of the algae. After evaluating the measurement data, it became clear that the theory of alternative equilibria in shallow water lakes is not tenable.

It turned out that there is actually only one sensible way to counteract the consequences of excessive nutrient input: to reduce it. It's not particularly original, but it's obvious and easy to understand.

Source: Helmholtz Center for Environmental Research (UFZ); Specialist article: Nature Communications,
doi: 10.1038/s41467-023-36043-9