Abstract
Since the beginning of the Anthropocene, lacustrine biodiversity has been influenced by climate change and human activities. These factors advance the spread of harmful cyanobacteria in lakes around the world, which affects water quality and impairs the aquatic food chain. In this study, we assessed changes in cyanobacterial community dynamics via sedimentary DNA (sedaDNA) from well-dated lake sediments of Lake Tiefer See, which is part of the Klocksin Lake Chain spanning the last 350 years. Our diversity and community analysis revealed that cyanobacterial communities form clusters according to the presence or absence of varves. Based on distance-based redundancy and variation partitioning analyses (dbRDA and VPA) we identified that intensified lake circulation inferred from vegetation openness reconstructions, δ13C data (a proxy for varve preservation) and total nitrogen content were abiotic factors that significantly explained the variation in the reconstructed cyanobacterial community from Lake Tiefer See sediments. Operational taxonomic units (OTUs) assigned to Microcystis sp. and Aphanizomenon sp. were identified as potential eutrophication-driven taxa of growing importance since circa common era (ca. CE) 1920 till present. This result is corroborated by a cyanobacteria lipid biomarker analysis. Furthermore, we suggest that stronger lake circulation as indicated by non-varved sediments favoured the deposition of the non-photosynthetic cyanobacteria sister clade Sericytochromatia, whereas lake bottom anoxia as indicated by subrecent- and recent varves favoured the Melainabacteria in sediments. Our findings highlight the potential of high-resolution amplicon sequencing in investigating the dynamics of past cyanobacterial communities in lake sediments and show that lake circulation, anoxic conditions, and human-induced eutrophication are main factors explaining variations in the cyanobacteria community in Lake Tiefer See during the last 350 years.
Highlights
The upsurge in human fertilizer and land-use change during the Anthropocene has intensified nutrient cycling
We suggest that stronger lake circulation as indicated by non-varved sediments favoured the deposition of the non-photosynthetic cyanobacteria sister clade Sericytochromatia, whereas lake bottom anoxia as indicated by subrecent- and recent varves favoured the Melainabacteria in sediments
Our study provides the first insights into the community structures of cyanobacteria and their non-photosynthetic sister lineages in Lake Tiefer See as archived in sediments that span the last 350 years
Summary
The upsurge in human fertilizer and land-use change during the Anthropocene has intensified nutrient cycling. Among the most susceptible ecosystems to anthropogenic activities and biodiversity losses is the freshwater ecosystem (Adrian et al 2009), where cyanobacteria dominance has resulted, amongst others, from intensified land usage and inordinate discharge of nutrients into lakes (Taranu et al 2015). Blooms of cyanobacteria form large clusters and colonies that move vertically in the water column by being able to counteract gas vesicle buoyancy via carbohydrate ballast readjustment (Pfeifer 2012). Taken together, these attributes coupled with their high susceptibility to human-induced changes make cyanobacteria ideal indicator organisms for investigating long term changes in lake ecosystems
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