We analyzed the depth distributions of benthic diatoms in two adjacent, but hydrologically distinct subalpine lakes (Lakes Soiernseen, S-Germany). Lake Unterer Soiernsee is affected by marked water-level fluctuations and is light-penetrated to the bottom most of the year, while Lake Oberer Soiernsee provides more stable conditions and an extended aphotic zone. Mixed samples of epiphytic, epilithic, epipsammic and epipelic periphyton were taken in one-meter depth steps by scuba divers. Most of the common benthic diatoms occurred in distinct depth-areas. RDA analyses showed that depth was strongly correlated with species distribution in both lakes. Depth-constrained cluster analyses indicated three distinct diatom community zones in each lake. A shallow littoral zone hosting mainly epiphytic and epilithic species and a deeper littoral zone with mainly epipsammic and epipelic taxa existed in both lakes. Additionally, a highly disturbed near-shore littoral zone with diatoms adapted to unstable conditions (aerophilic taxa, pioneer species) was found in Lake Unterer Soiernsee, and a deep-water pelagic zone with mainly planktonic taxa in Lake Oberer Soiernsee. Light availability, substrate, physical stressors and nutrient concentrations were linked closely with water depth. While light availability affected the ratio of benthic and planktonic diatoms, substrate type influenced benthic diatom assemblage structures. Diatoms occurring in surficial sediments of the aphotic zone represent an ideal cross-section of the recent diatom assemblage of the lake, including benthic and planktonic species. However, sediment samples taken in light-flooded depths are inappropriate for studies based on shifts between benthic and planktonic taxa, because in situ benthic species dominate the surface-sediment assemblages, while settled tychoplanktonic and planktonic species occur less frequently. A diatom-inferred depth model was created for each lake to prove the usability for down-core studies using weighted-averaging approaches. For both lakes these models are highly appropriate to reconstruct past fluctuations in water-transparency or lake-level. With regard to the development of diatom-based TP-transfer-functions for Bavarian mountain lakes, we found it is highly important to consider lake depth and transparency. Based on the findings of this study we recommend the creation of two different training-sets, one for deep or low-transparency lakes with an aphotic zone including both benthic and planktonic diatoms, and another one for shallow, clear water lakes solely using benthic diatoms.

中文翻译：

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与光照和基质相关的湖泊底栖硅藻组合的深度分布：对古湖泊学研究的影响

我们分析了两个相邻但水文不同的亚高山湖泊（Soiernseen，S-Germany）中底栖硅藻的深度分布。Unterer Soiernsee 湖受明显的水位波动影响，一年中的大部分时间都透光到底部，而 Oberer Soiernsee 湖提供更稳定的条件和扩展的无光区。水肺潜水员以一米深的台阶采集附生、附生、附生和附生附生生物的混合样本。大多数常见的底栖硅藻出现在不同的深度区域。RDA 分析表明，深度与两个湖泊的物种分布密切相关。深度约束聚类分析表明每个湖泊中存在三个不同的硅藻群落区。两个湖泊都存在一个以附生和附生物种为主的浅沿岸带和一个以附生和附生类群为主的更深沿岸带。此外，在 Unterer Soiernsee 湖发现了一个高度扰动的近岸沿岸带，硅藻适应不稳定的条件（好氧类群，先锋物种），在 Oberer Soiernsee 湖发现了一个主要以浮游生物类群为主的深水远洋带。光照、底物、物理压力源和养分浓度与水深密切相关。虽然光照影响底栖和浮游硅藻的比例，底物类型影响底栖硅藻组合结构。发生在无光区表层沉积物中的硅藻代表了湖泊最近硅藻组合的理想横截面，包括底栖和浮游物种。然而，在浅水淹没深度采集的沉积物样本不适合基于底栖和浮游类群之间转换的研究，因为原位底栖物种在地表沉积物组合中占主导地位，而定居的浮游物种和浮游物种的出现频率较低。为每个湖泊创建了一个硅藻推断深度模型，以证明使用加权平均方法进行芯下研究的可用性。对于这两个湖泊，这些模型非常适合重建过去水透明度或湖泊水位的波动。关于巴伐利亚山区湖泊基于硅藻的 TP 传递函数的开发，我们发现考虑湖泊深度和透明度非常重要。根据这项研究的结果，我们建议创建两个不同的训练集，