Abstract Lake Erie experiences annual summer cyanobacterial harmful algal blooms (HABs), comprised mostly of non-nitrogen-fixing Microcystis, due to excess nitrogen (N) and phosphorus (P) inputs (eutrophication). Lake Erie's watershed is mostly agricultural, and fertilizers, manure, and drainage practices contribute to high nutrient loads. This study aimed to clarify the role of western Lake Erie sediments in either exacerbating or mitigating conditions that fuel HABs via recycling and/or removal, respectively, of excess N and reactive P. Sediment-water interface N and orthophosphate (ortho-P) dynamics and functional gene analyses of key N transformations were evaluated during a dry, low HAB year (2016) and a wet, high HAB year (2017). On average, western basin sediments were a net N sink and thus perform a valuable ecosystem service via N removal. However, sediments were a source of ortho-P and chemically reduced N. Western basin sediments can theoretically remove 29% of average annual watershed total N loading. Denitrification rates were lower during the high (2017) versus low bloom year (2016), suggesting that high external N loading and large HABs inhibit the capacity of sediments to perform that ecosystem service. Despite being a net N sink on average, western basin sediments released ammonium and urea, chemically reduced N forms that are energetically conducive to non-N-fixing, toxin-producing cyanobacterial HABs, especially during the critical period of low external loading and high biomass. These results support other recent work highlighting the urgent need to include N cycling and internal load dynamics in ecosystem models and mitigation efforts for eutrophic systems.

中文翻译：

---

通过定量养分循环途径和选定的基因丰度来评估伊利湖西部作为生态系统服务的沉积物

摘要 伊利湖每年都会经历夏季蓝藻有害藻华 (HAB)，主要由非固氮微囊藻组成，这是由于氮 (N) 和磷 (P) 输入过多（富营养化）。伊利湖的流域主要是农业流域，肥料、粪便和排水措施导致高营养负荷。本研究旨在阐明伊利湖西部沉积物在加剧或缓解 HABs 的条件中的作用，分别通过回收和/或去除过量的 N 和反应性 P。 沉积物 - 水界面 N 和正磷酸盐 (ortho-P) 动力学在干旱、低 HAB 年（2016 年）和潮湿、高 HAB 年（2017 年）期间评估了关键氮转化的功能基因分析。一般，西部盆地沉积物是净氮汇，因此通过去除氮提供有价值的生态系统服务。然而，沉积物是原磷和化学还原氮的来源。西部盆地沉积物理论上可以去除流域年平均总氮负荷的 29%。与低盛期（2016 年）相比，高盛期（2017 年）的反硝化率较低，这表明高外部 N 负荷和大 HAB 抑制了沉积物执行生态系统服务的能力。尽管平均而言是净氮汇，但西部盆地沉积物释放出铵和尿素，化学还原的氮形式在能量上有利于非固氮、产生毒素的蓝藻 HAB，尤其是在低外部负荷和高生物量的关键时期.