作者：Scott, J.T., Taylor, J.M., Andersen, I.M., Hoke, A.K. & Kelly, P.T.

Although phosphorus (P) has been the primary focus of lake eutrophication management efforts globally, we show that reducing nitrogen (N) inputs to shallow P-rich lakes can rapidly reverse accelerated eutrophication. We conducted a long-term field mesocosm manipulation experiment testing the effects of variable N and P stoichiometry on the eutrophication of lakes, particularly the comparative productivity of lakes with low N:P inputs versus high N:P inputs and the subsequent effects of reducing N inputs while maintaining P inputs. Nitrogen enrichment in excess of balanced N:P ratios (20-50 molar) resulted in phytoplankton biomass well above thresholds indicative of healthy lake ecosystems. After 4 years of both N and P enrichment, we eliminated N fertilization while maintaining P fertilization and observed a 57 +/- 3.1% reduction in phytoplankton biomass across all fertilization treatments. Comparative analysis of our experimental results with the 2022 U.S. National Lakes Assessment suggested that excess N is contributing to eutrophication for approximately 40% of U.S. lakes. Despite the capacity of lake ecosystems to import N from N fixation, reducing N inputs to shallow P-rich lakes has the potential to decrease phytoplankton biomass and the harmful effects of accelerated eutrophication.

尽管磷（P）一直是全球湖泊富营养化管理工作的主要关注对象，但我们的研究表明，减少富磷浅水湖泊的氮（N）输入能够快速逆转加速的富营养化进程。我们开展了一项长期的野外中宇宙操控实验，旨在测试不同氮磷化学计量比对湖泊富营养化的影响，特别是氮磷输入比低的湖泊与氮磷输入比高的湖泊在生产力方面的差异，以及在保持磷输入不变的情况下减少氮输入所产生的后续影响。当氮的富集超过平衡的氮磷比（20-50摩尔比）时，浮游植物生物量会远高于指示湖泊生态系统健康的阈值。在对氮和磷进行了4年的富集处理后，我们停止了氮的添加，同时保持磷的添加，结果观察到所有施肥处理组的浮游植物生物量均减少了57±3.1%。将我们的实验结果与2022年美国国家湖泊评估报告进行对比分析后发现，大约 40% 的美国湖泊中，过量的氮是导致富营养化的原因之一。尽管湖泊生态系统能够通过固氮作用获取氮，但减少富磷浅水湖泊的氮输入，仍有可能降低浮游植物生物量，并减轻加速的富营养化所带来的有害影响。

（来源： Environmental Science & Technology  2025 Issue 42  DOI: 10.1021/acs.est.5c05392）