Diatom communities are composed of three distinct water-depth-associated assemblages: a nearshore benthic assemblage, a deep-water benthic assemblage, and a primarily planktonic assemblage. Light attenuation with depth has been hypothesized to be the factor that controls benthic-to-planktonic (B:P) assemblage transitions. Previous studies, however, could not distinguish between the individual effects of light and temperature on diatom assemblage transition because the depth of the B:P transition occurred at or near the depth of the thermocline. This has caused confusion regarding which factor is the more influential variable on benthic-planktonic diatom assemblage transition in surface sediments along water-depth transects in lakes. Two boreal lakes in northeast Ontario were selected to examine this problem. The study lakes are sufficiently deep and clear (Secchi disk depths ~ 9–10 m; dissolved organic carbon ~ 3 mg/L), making it possible to distinguish between the depth of 1% light penetration and the depth of the thermocline. Surface sediment samples were collected along water-depth transects from these lakes to examine intra-lake diatom assemblage structure. In both lakes, the water depth of the diatom assemblage B:P transition was closely associated with the depth of the ~ 1% photosynthetically active radiation value, and was well below the depth of the thermocline, suggesting that light penetration has more influence on this transition than does the thermocline. Because temporal fluxes in nutrients and DOC concentrations can attenuate light, understanding how the light regime influences benthic diatoms in lakes can help inform interpretations of diatom assemblage changes in paleolimnological studies.

中文翻译：

---

在安大略省北部（加拿大）的贫营养和中营养湖泊中，硅藻组合受到光衰减的控制

硅藻群落由三个不同的与水深相关的组合组成：近岸底栖组合、深水底栖组合和主要浮游生物组合。已经假设随着深度的光衰减是控制底栖到浮游生物 (B:P) 组合过渡的因素。然而，之前的研究无法区分光和温度对硅藻组合转变的个体影响，因为 B:P 转变的深度发生在温跃层的深度处或附近。这引起了关于哪个因素是影响湖泊水深横断面表层沉积物中底栖-浮游硅藻组合转变的更大影响变量的混淆。选择安大略省东北部的两个北方湖泊来研究这个问题。研究的湖泊足够深且清澈（Secchi 盘深度约 9-10 m；溶解有机碳约 3 mg/L），可以区分 1% 光穿透的深度和温跃层的深度。沿着这些湖泊的水深横断面收集表层沉积物样本，以检查湖内硅藻组合结构。在两个湖泊中，硅藻组合 B:P 转变的水深与~1% 光合有效辐射值的深度密切相关，并且远低于温跃层的深度，表明光穿透对此影响更大过渡比温跃层。因为营养物质和 DOC 浓度的时间通量会衰减光，