藻花

dāng dàn huò lín huò liǎng zhě cún zài shù liàng hěn shǎo shí bù chū xiàn zhè zhǒng zǎo huā

当氮或磷或两者存在数量很少时，不出现这种藻花。

Such water blooms do not occur when nitrogen or phosphorus or both are present in very limited amounts.