This 6-month study characterized the contribution of deep chlorophyll maximum (DCM) to lake phytoplankton diversity and primary production, in relation to stratification during the ice-free season. Phytoplankton and zooplankton dynamics were examined with environmental drivers in a small stratified lake that presents vertical gradients of light and nutrients. The phytoplankton, first composed of diatoms and chrysophyceae, shifted to cyanobacteria in mid-July. With stratification increase, surface nutrient limitation appeared to favor motile species characteristic of oligotrophic environments above a deep layer of filamentous cyanobacteria, fueled by the vertical nutrient fluxes from sediment. The DCM contributed on average to 33% (but up to 60%) of total production during the strongest summer stratification period. In late summer, as stratification was eroding, the vertical gradient of nutrients was reduced, but light attenuation with depth increased. Distinct assemblages were identified between surface and deep layer with shade-adapted species. The contribution of DCM was reduced to 10%. Zooplankton community varied in conjunction with phytoplankton and stratification. Our study demonstrates no benefit of DCM for taxonomic and functional diversity and a limited contribution to total production. The depths over which phytoplankton use separate spatial niches may be lesser in a 6-m-deep lake compared with deeper stratified lakes.

中文翻译：

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小层湖中最大叶绿素含量对初级生产，浮游植物组合和多样性的贡献

这项为期6个月的研究的特点是，与无冰季节的分层有关，深层叶绿素最大值（DCM）对湖泊浮游植物多样性和初级生产的贡献。浮游植物和浮游动物的动力学由环境驱动器在一个小型的分层湖泊中进行，该湖泊呈现出光和养分的垂直梯度。最初由硅藻和金藻科组成的浮游植物在7月中旬转移到了蓝细菌。随着分层的增加，表面养分的限制似乎有利于在丝状蓝细菌深层以上的贫营养环境的运动性物种，这是由沉积物的垂直养分流推动的。在最强的夏季分层期间，DCM平均贡献了总产量的33％（但最高达到60％）。在夏末，随着分层的侵蚀，养分的垂直梯度减小，但随着深度的增加，光衰减增加。在具有阴影适应性物种的表层和深层之间发现了不同的组合。DCM的贡献降低到10％。浮游动物群落与浮游植物和分层有关。我们的研究表明DCM对于分类和功能多样性没有好处，并且对总产量的贡献有限。与更深的分层湖泊相比，在6米深的湖泊中，浮游植物使用单独的空间生态位的深度可能较小。浮游动物群落与浮游植物和分层有关。我们的研究表明DCM对于分类和功能多样性没有好处，并且对总产量的贡献有限。与更深的分层湖泊相比，在6米深的湖泊中，浮游植物使用单独的空间生态位的深度可能较小。浮游动物群落与浮游植物和分层有关。我们的研究表明DCM对于分类和功能多样性没有好处，对总产量的贡献有限。与更深的分层湖泊相比，在6米深的湖泊中，浮游植物使用单独的空间生态位的深度可能较小。