1. Comprehensive assessments of contemporary diatom distributions across the Arctic remain scarce. Furthermore, studies tracking species compositional differences across space and time, as well as diatom responses to climate warming, are mainly limited to paleolimnological studies due to a lack of routine monitoring in lakes and streams across vast areas of the Arctic.
2. The study aims to provide a spatial assessment of contemporary species distributions across the circum-Arctic, establish contemporary biodiversity patterns of diatom assemblages to use as reference conditions for future biomonitoring assessments, and determine pre-industrial baseline conditions to provide historical context for modern diatom distributions.
3. Diatom assemblages were assessed using information from ongoing regulatory monitoring programmes, individual research projects, and from surface sediment layers obtained from lake cores. Pre-industrial baseline conditions as well as the nature, direction and magnitude of changes in diatom assemblages over the past c.200 years were determined by comparing surface sediment samples (i.e. containing modern assemblages) with a sediment interval deposited prior to the onset of significant anthropogenic activities (i.e. containing pre-1850 assemblages), together with an examination of diatoms preserved in contiguous samples from dated sediment cores.
4. We identified several biotypes with distinct diatom assemblages using contemporary diatom data from both lakes and streams, including a biotype typical for High Arctic regions. Differences in diatom assemblage composition across circum-Arctic regions were gradual rather than abrupt. Species richness was lowest in High Arctic regions compared to Low Arctic and sub-Arctic regions, and higher in lakes than in streams. Dominant diatom taxa were not endemic to the Arctic. Species richness in both lakes and streams reached maximum values between 60°N and 75°N but was highly variable, probably reflecting differences in local and regional environmental factors and possibly sampling effort.
5. We found clear taxon-specific differences between contemporary and pre-industrial samples that were often specific to both ecozone and lake depth. Regional patterns of species turnover (β-diversity) in the past c.200 years revealed that regions of the Canadian High Arctic and the Hudson Bay Lowlands to the south showed most compositional change, whereas the easternmost regions of the Canadian Arctic changed least. As shown in previous Arctic diatom studies, global warming has already affected these remote high latitude ecosystems.
6. Our results provide reference conditions for future environmental monitoring programmes in the Arctic. Furthermore, diatom taxa identification and harmonisation require improvement, starting with circum-Arctic intercalibrations. Despite the challenges posed by the remoteness of the Arctic, our study shows the need for routine monitoring programmes that have a wide geographical coverage for both streams and lakes.

中文翻译：

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湖泊和溪流中北极硅藻组合的生物多样性模式：生物监测的当前参考条件和历史背景

1. 对北极当代硅藻分布的综合评估仍然很少。此外，由于缺乏对北极广大地区湖泊和溪流的常规监测，追踪物种组成在空间和时间上的差异以及硅藻对气候变暖的反应的研究主要局限于古湖沼学研究。
2. 该研究旨在对整个北极圈的当代物种分布进行空间评估，建立当代硅藻组合的生物多样性模式，作为未来生物监测评估的参考条件，并确定工业前基线条件，为现代硅藻分布提供历史背景.
3. 使用来自正在进行的监管监测计划、个别研究项目和从湖芯获得的表层沉积层的信息评估硅藻组合。工业化前的基线条件以及过去硅藻组合变化的性质、方向和幅度c．200 年是通过比较地表沉积物样本（即包含现代组合）与在重要的人为活动开始之前沉积的沉积物间隔（即包含 1850 年之前的组合）以及检查保存在来自年代久远的沉积物的连续样本中的硅藻来确定的核心。
4. 我们使用来自湖泊和溪流的当代硅藻数据确定了几种具有不同硅藻组合的生物型，包括高北极地区典型的生物型。环北极地区硅藻组合组成的差异是渐进的，而不是突然的。与低北极和亚北极地区相比，高北极地区的物种丰富度最低，湖泊高于溪流。主要的硅藻类群不是北极特有的。湖泊和溪流中的物种丰富度在 60°N 和 75°N 之间达到最大值，但变化很大，可能反映了当地和区域环境因素的差异以及可能的采样努力。
5. 我们发现当代和工业化前样本之间存在明显的分类群特异性差异，这些差异通常特定于生态区和湖泊深度。过去物种周转（β-多样性）的区域模式c．200 年表明，加拿大北极高地和南部的哈德逊湾低地地区的成分变化最大，而加拿大北极最东部的地区变化最小。正如之前的北极硅藻研究所示，全球变暖已经影响了这些偏远的高纬度生态系统。
6. 我们的研究结果为北极未来的环境监测计划提供了参考条件。此外，硅藻类群的识别和协调需要改进，从环北极相互校准开始。尽管北极地处偏远带来了挑战，但我们的研究表明，需要对河流和湖泊进行广泛地理覆盖的常规监测计划。