Washing powder contains phosphorus compounds, which can combine with calcium and magnesium ions in water to reduce the hardness of water, thus improving the decontamination effect of bathing. But after washing, a large amount of phosphorus-containing wastewater is produced. Because phosphorus is a nutrient for plant growth, the increase of phosphorus will make the plants in algae multiply. Algae will consume dissolved oxygen in water, leading to water quality deterioration and a large number of fish deaths. At this time, the water body is eutrophic.

We know that nitrogen and phosphorus are the most important nutrients that determine the growth of algae. So, can nitrogen limitation prevent water eutrophication? I can't. Because algae can directly fix the nitrogen they need from the air, and after the algae dies, microorganisms will decompose their "remains" and the obtained nitrogen can be reused by other algae.

Scientists have learned through experiments that only by limiting phosphorus in water can eutrophication be prevented. Therefore, limiting the use of phosphorus-containing washing powder can effectively control the eutrophication of water bodies.