水体富营养化Eutrophication

藻类按雷德菲尔德比例 C:N:P ≈ 106:16:1 吸收营养，淡水中磷通常是限制因子，近海中氮常是限制因子。营养过剩时藻类暴发，死亡后被细菌分解大量消耗溶解氧，底层水变为缺氧甚至无氧状态，产生 H₂S 和 NH₃，形成“死区”。部分蓝藻（如微囊藻）还会释放微囊藻毒素，威胁饮用水安全。

Algae take up nutrients in roughly the Redfield ratio C:N:P ≈ 106:16:1; phosphorus is usually limiting in fresh water and nitrogen in coastal seas. With excess nutrients algae bloom, and when they die bacterial decay uses up dissolved oxygen, making bottom water hypoxic or anoxic and releasing H₂S and NH₃, creating 'dead zones'. Some cyanobacteria, such as Microcystis, also produce microcystins that threaten drinking water.

eutrophic 一词由德国湖沼学家韦伯在 1907 年用于描述营养丰富的湖泊。1960 年代北美伊利湖、欧洲多处湖泊严重富营养化，加拿大辛德勒在实验湖区的全湖实验（1970 年代）证明磷是关键因素，推动了含磷洗衣粉禁令。

The German limnologist Weber used the term eutrophic in 1907 for nutrient-rich lakes. Severe eutrophication of Lake Erie and many European lakes in the 1960s led to whole-lake experiments by David Schindler at Canada's Experimental Lakes Area in the 1970s, which showed phosphorus to be the key factor and prompted bans on phosphate detergents.

营养物质来自农田化肥流失、畜禽养殖废水、生活污水和含磷洗涤剂。治理措施包括污水厂脱氮除磷（生物脱氮、化学沉淀除磷：Fe³⁺ + PO₄³⁻ → FePO₄↓）、控制面源污染、清淤和生态修复。中国太湖、滇池都曾发生严重蓝藻水华。

Nutrients come from fertiliser runoff, livestock wastewater, sewage and phosphate detergents. Controls include nitrogen and phosphorus removal at treatment plants (biological denitrification and chemical precipitation, Fe³⁺ + PO₄³⁻ → FePO₄↓), limiting diffuse runoff, dredging and ecological restoration. China's Taihu and Dianchi lakes have both suffered severe cyanobacterial blooms.