Abstract Deep chlorophyll maxima (DCM) are common in stratified lakes and oceans, and phytoplankton growth within DCM often contributes significantly to total system production. Theory suggests that properties of DCM should be predictable by trophic state, with DCM becoming deeper, broader, and less productive with greater oligotrophy. However, rigorous tests of these expectations are lacking in freshwater systems. We use data generated by the U.S. EPA from 1996 to 2017, including in situ profile data for temperature, photosynthetically active radiation (PAR), chlorophyll, beam attenuation (c p), and dissolved oxygen (DO), to investigate patterns in DCM across lakes and over time. We consider trophic state, 1% PAR depth (z 1%), thermal structure, and degree of photoacclimation as potential drivers of DCM characteristics. DCM depth and thickness generally increased while DCM chlorophyll concentration decreased with decreasing trophic state index (greater oligotrophy). The z 1% was a stronger predictor of DCM depth than thermal structure. DCM in meso‐oligotrophic waters were closely aligned with maxima in c p and DO saturation, suggesting they are autotrophically productive. However, the depths of these maxima diverged in ultra‐oligotrophic waters, with DCM occurring deepest. This is likely a consequence of photoacclimation in high‐transparency waters, where c p can be a better proxy for phytoplankton biomass than chlorophyll. Our results are generally consistent with expectations from DCM theory, but they also identify specific gaps in our understanding of DCM in lakes, including the causes of multiple DCM, the importance of nutriclines, and the processes forming DCM at higher light levels than expected.

中文翻译：

---

跨越营养状态梯度的深层叶绿素最大值：劳伦斯大湖的案例研究

摘要 深层叶绿素最大值 (DCM) 在分层的湖泊和海洋中很常见，DCM 内的浮游植物生长通常对整个系统的生产有显着贡献。理论表明 DCM 的特性应该可以通过营养状态来预测，随着 DCM 变得更深、更广、生产力更低，营养状态更大。然而，淡水系统缺乏对这些期望的严格测试。我们使用美国环保署 1996 年至 2017 年生成的数据，包括温度、光合有效辐射 (PAR)、叶绿素、光束衰减 (cp) 和溶解氧 (DO) 的原位剖面数据，以研究跨湖泊的 DCM 模式随着时间的推移。我们将营养状态、1% PAR 深度 (z 1%)、热结构和光驯化程度视为 DCM 特性的潜在驱动因素。DCM 深度和厚度通常增加，而 DCM 叶绿素浓度随着营养状态指数的降低（更大的贫营养）而降低。z 1% 比热结构更能预测 DCM 深度。中低营养水域中的 DCM 与 cp 和 DO 饱和度的最大值密切相关，表明它们是自养生产的。然而，这些最大值的深度在超贫营养水域中发生分歧，DCM 发生得最深。这可能是高透明度水域中光驯化的结果，其中 cp 可以比叶绿素更好地代表浮游植物生物量。我们的结果总体上与 DCM 理论的预期一致，但它们也确定了我们对湖泊中 DCM 理解的具体差距，包括多种 DCM 的原因、营养物质的重要性、