作者：Kharbush, J.J., Robinson, R.S. & Carter, S.J.

Western Lake Erie experiences an annual, toxic cyanobacterial harmful algal bloom (cyanoHAB), primarily caused by excess anthropogenic inputs of nitrogen (N) and phosphorous (P). Because the non-N fixing cyanobacteria species Microcystis dominates these blooms, N availability is hypothesized to play a central role in cyanoHAB progression, as well as production of the N-rich toxin microcystin. Many previous studies focused on nitrate because it is the most abundant N substrate during bloom initiation. However, recent work implicated reduced N substrates like ammonium and dissolved organic N (DON) in promoting greater bloom biomass and longevity. To examine the relative importance of oxidized and reduced N substrates to phytoplankton during different bloom stages, we measured concentrations and natural abundance delta N-15 isotope values of dissolved N substrates and phytoplankton biomass throughout the entirety of the 2020 cyanoHAB in Western Lake Erie. The results provide the first data on DON dynamics and composition in Western Lake Erie, and suggest that phytoplankton, including Microcystis, likely relied on N regenerated from the DON pool in later bloom stages. In addition, the stable isotope data confirm the importance of nitrate delivered via the Maumee River to cyanobacterial growth and toxin production.

伊利湖西部每年都会发生有毒的蓝藻有害水华（cyanoHAB），这主要是由人为输入的过量氮（N）和磷（P）引起的。由于非固氮蓝藻种类微囊藻在这些水华中占主导地位，因此氮的可获得性被认为在蓝藻水华的发展以及富含氮的毒素微囊藻毒素的产生中起着核心作用。许多先前的研究都聚焦于硝酸盐，因为它是水华发生初期最丰富的氮底物。然而，最近的研究表明，像铵和溶解性有机氮（DON）这样的还原态氮底物有助于增加水华生物量并延长其持续时间。为了探究在水华不同阶段，氧化态和还原态氮底物对浮游植物的相对重要性，我们在 2020 年伊利湖西部整个蓝藻水华期间，测量了溶解性氮底物和浮游植物生物量的浓度以及自然丰度 δN-15 同位素值。研究结果首次提供了伊利湖西部溶解性有机氮动态和组成的数据，并表明包括微囊藻在内的浮游植物在水华后期可能依赖于从溶解性有机氮库中再生的氮。此外，稳定同位素数据证实了通过莫米河输送的硝酸盐对蓝藻生长和毒素产生的重要性。

（来源：Limnology and Oceanography 2023 DOI: 10.1002/lno.12311）