Benthic diatoms are commonly used for palaeoenvironmental reconstruction in Arctic regions, but interpretation of their ecology remains challenging. We studied epilithic diatom assemblages from the shallow margins of 19 lakes from three areas (coast-inland-ice sheet margin) along a climate gradient in Kangerlussuaq, West Greenland during two periods; shortly after ice-off (spring) and in the middle of the growth season (summer). We aimed to understand the distribution of Arctic epilithic diatoms in relation to water chemistry gradients during the two seasons, to investigate their incorporation into lake sediments and to assess their applicability as palaeoenvironmental indicators. Diatoms were correlated with nutrients in the spring and alkalinity/major ions in the summer, when nutrients were depleted; approximately half of the variance explained was independent of spatial factors. When categorised by functional attributes, diatom seasonal succession differed among regions with the most obvious changes in inland lakes where summer temperatures are warmer, organic nutrient processing is prevalent and silicate is limiting. These conditions led to small, motile and adnate diatoms being abundant in inland lakes during the summer (Nitzschia spp., Encyonopsis microcephala), as these functional attributes are suited to living within complex mats of non-siliceous microbial biofilms. Seasonal succession in silica-rich lakes at the coast was less pronounced and assemblages included Tabellaria flocculosa (indicating more acidic conditions) and Hannaea arcus (indicating input from inflowing rivers). The nitrogen-fixing diatom Epithemia sorex increased from the coast to the ice sheet, negatively correlating with a gradient of reactive nitrogen. The presence of this diatom in Holocene sediment records alongside cyanobacterial carotenoids during arid periods of low nitrogen delivery, suggests that it is a useful indicator of nitrogen limitation. Nitzschia species appear to be associated with high concentrations of organic carbon and heterotrophy, but their poor representation in West Greenland lake sediments due to taphonomic processes limits their palaeoenvironmental application in this region. Proportions of epilithic taxa in lake sediment records of coastal lakes increased during some wetter periods of the Holocene, suggesting that snowpack-derived nutrient delivery may offer diatom taxa living at lake margins a competitive advantage over planktonic diatoms during the “moating” ice melt period. Thus, further research investigating linkages between epilithic diatoms, snowpack and nutrient delivery in seasonally frozen lakes is recommended as these taxa live on the ‘front-line’ during the spring and may be especially sensitive to changes in snowmelt conditions.

中文翻译：

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格陵兰西南部湖泊古环境解释中附生硅藻的功能属性

底栖硅藻常用于北极地区的古环境重建，但对其生态的解释仍然具有挑战性。我们研究了两个时期内格陵兰西部康克鲁斯瓦克气候梯度三个区域（海岸-内陆-冰盖边缘）的 19 个湖泊浅边缘的附生硅藻组合；结冰后不久（春季）和生长季节中期（夏季）。我们的目的是了解北极附生硅藻在两个季节的分布与水化学梯度的关系，调查它们与湖泊沉积物的结合，并评估它们作为古环境指标的适用性。硅藻在春季与养分相关，而在夏季养分枯竭时与碱度/主要离子相关；解释的方差中约有一半与空间因素无关。当按功能属性分类时，内陆湖泊的硅藻季节性演替存在差异，夏季气温较高、有机养分加工普遍、硅酸盐含量有限的内陆湖泊变化最为明显。这些条件导致夏季内陆湖泊（Nitzschia spp.，Encyonopsis microcephala）中大量存在小的、活动的和贴壁的硅藻，因为这些功能特性适合生活在非硅质微生物生物膜的复杂垫中。海岸富含二氧化硅的湖泊的季节性演替不那么明显，组合包括 Tabellaria flocculosa（表明酸性条件更强）和 Hannaea arcus（表明来自流入河流的输入）。固氮硅藻 Epithemia sorex 从海岸到冰盖增加，与活性氮的梯度呈负相关。在低氮输送的干旱时期，全新世沉积物中这种硅藻的存在与蓝藻类胡萝卜素一起记录，表明它是氮限制的有用指标。Nitzschia 物种似乎与高浓度的有机碳和异养有关，但由于埋藏过程，它们在西格陵兰湖沉积物中的代表性较差，限制了它们在该地区的古环境应用。沿海湖泊湖泊沉积记录中附石类群的比例在全新世的一些湿润时期增加，表明在“护城河”冰融化期间，积雪衍生的养分输送可能为生活在湖边的硅藻类群提供优于浮游硅藻的竞争优势。因此，建议进一步研究调查季节性冰冻湖泊中附生硅藻、积雪和养分输送之间的联系，因为这些分类群在春季生活在“前线”，可能对融雪条件的变化特别敏感。