The Microbial Community in Oxygen Deficient Lakes : What DNA Can Tell Us About Two Lakes in Northern Norway | Mikroorganismsamhällen i syrefattiga sjöar : vad DNA kan säga om två sjöar I norra Norge
2025
Edling, Saga
Aquatic ecosystems are increasingly impacted by global climate change and anthropogenic pressures, with expanding anoxic zones in oceans and lakes posing challenges to ecosystem functioning. This study investigates how microbial communities differ between oxygenated and oxygen-deficient lakes by comparing two lakes in northern Norway: Finnfjordvattnet, a freshwater lake, and Rossfjordvattnet, a brackish lake with a permanently anoxic bottom due to saltwater intake. Water samples collected at the lakes were assesed for Community compossition through high-throughput sequencing of 16S and 18S rRNA gene fragments from DNA extracted from the two lakes. Analysis revealed significant differences in community composition between the lakes and across oxygen gradients within Rossfjordvattnet. Rossfjordvattnet exhibited dissimilar microbial assemblages in oxic, hypoxic, and anoxic layers, which was tested with an ANOSIM and confirmed to be significant. Bacteria dominated all samples, while archaea such as Crenarchaeota and Nanoarchaeota made up a meaningful part of the community in Rossfjordvattnet, corroborating the need of including archaea in microbial community studies. Unexpectedly, Crenarchaeota were especially prevalent in the oxygenated upper layers, possibly due to their role in aerobic ammonia oxidation under saline conditions. The results highlight the influence of oxygen availability and salinity on microbial community structure and discusses roles for taxonomic groups less often seen in the context of lakes such as Bacteriodota and Crenarchaeota. These findings underscore the complexity of microbial dynamics in aquatic systems and point to the need for further research on archaea and microbial functions in waterbodies with anoxic bottoms due to a saline gradient.
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