作者：Kong, X., Determann, M., Andersen, T.K., et al.

Phosphorus (P) precipitation is among the most effective treatments to mitigate lake eutrophication. However, after a period of high effectiveness, studies have shown possible re-eutrophication and the return of harmful algal blooms. While such abrupt ecological changes were attributed to the internal P loading, the role of lake warming and its potential synergistic effects with internal loading, thus far, has been understudied. Here, in a eutrophic lake in central Germany, we quantified the driving mechanisms of the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). A process-based lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring data set covering contrasting trophic states. Model analyses suggested that the internal P release accounted for 68% of the cyanobacterial biomass proliferation, while lake warming contributed to 32%, including direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further showed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. Our study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The warming effects on cyanobacteria via promoting internal loading need more attention in lake management, particularly for urban lakes.

磷（P）沉淀是缓解湖泊富营养化最有效的处理方法之一。然而，在一段高效期之后，研究表明可能会出现再次富营养化以及有害藻华的复发。虽然这种突然的生态变化被认为是由内部磷负荷引起的，但迄今为止，湖泊变暖及其与内部负荷潜在的协同效应所起的作用尚未得到充分研究。本文以德国中部的一个富营养化湖泊为研究对象，量化了2016年（首次磷沉淀处理30年后）该湖泊突然再次富营养化和蓝藻水华爆发的驱动机制。利用涵盖不同营养状态的高频监测数据集，建立了基于过程的湖泊生态系统模型（GOTM-WET）。模型分析表明，内部磷释放对蓝藻生物量增长的贡献率为 68%，而湖泊变暖的贡献率为 32%，其中包括通过促进生长产生的直接影响（18%）和通过加剧内部磷负荷产生的协同效应（14%）。模型进一步显示，这种协同效应源于湖泊下层水体长期变暖及缺氧。我们的研究揭示了湖泊变暖在促进再次富营养化湖泊中蓝藻水华爆发方面的重要作用。在湖泊管理中，尤其是城市湖泊的管理，需要更多关注变暖通过促进内部负荷对蓝藻产生的影响。

(来源：Environmental Science & Technology 2023 DOI: 10.1021/acs.est.2c07181）