Abstract
Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. We demonstrate that climate changes and deforestation can drive recurrent microbial blooms, inhibiting the recovery of freshwater ecosystems for hundreds of millennia. From the stratigraphic successions of the Sydney Basin, Australia, our fossil, sedimentary and geochemical data reveal bloom events following forest ecosystem collapse during the most severe mass extinction in Earth’s history, the end-Permian event (EPE; c. 252.2 Ma). Microbial communities proliferated in lowland fresh and brackish waterbodies, with algal concentrations typical of modern blooms. These initiated before any trace of post-extinction recovery vegetation but recurred episodically for >100 kyrs. During the following 3 Myrs, algae and bacteria thrived within short-lived, poorly-oxygenated, and likely toxic lakes and rivers. Comparisons to global deep-time records indicate that microbial blooms are persistent freshwater ecological stressors during warming-driven extinction events.
Highlights
Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers
Non-metric multidimensional scaling of the palynofacies supports these phases as indicated by their discrete regions in ordination space (Fig. 3)
The “pre-endPermian event (EPE)” phase is dominated by abundant wood, leaves, and pollen typical of wetland glossopterid gymnosperms (Fig. 2)
Summary
Harmful algal and bacterial blooms linked to deforestation, soil loss and global warming are increasingly frequent in lakes and rivers. The most consequential long-term changes on land included the abrupt demise of wetland glossopterid forests of the temperate Southern Hemisphere[10] and the tropical coal-forming forests of east Asia[11] These were some of the most enduring and widespread biomes in Earth history, and their disappearance initiated a global “coal gap” in the rock record, reflecting a major reduction in atmospheric carbon drawdown that persisted for several million years[12]. A series of recent, high-precision age constraints[13,14,15], coupled with a well-resolved spore-pollen zonation scheme[10,16], crowns the Sydney Basin, Australia, as the standard reference succession for upper Permian and Lower Triassic continental fossil and rock unit correlations in the Southern Hemisphere These strata provide a near-continuous record of coastal plain environments through the EPE13,14,16,17 We propose that the proliferation of microbial communities was both a symptom of continental ecosystem collapse, and a cause of its delayed recovery
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