Springs are hotspots of microbial diversity in the hydrologic continuum

Freshwater springs worldwide are recognised for their high level of ecological diversity and specialisation. However, their role in harbouring and transmitting biota from below ground into freshwater catchments remains poorly studied. Here we investigate the ecohydrological role of springs across the groundwater-spring-surface water continuum in Australia’s iconic Great Artesian Basin, using microbial environmental DNA and the naturally occurring radioisotope tracer, radon. By analysing taxonomic richness and shared/unique taxa across several aquifer (n = 7), spring (n = 15) and surface water samples (n = 13), we show that the greatest biodiversity occurs in springs. Functional trait analysis and identification of indicator taxa associated with variation in ²²²Rn further demonstrates the groundwater-dependence of catchments in the region and that springs are a key link by which sub-surface microbial diversity and functional signatures are exported into surface water bodies. Springs in the Great Artesian Basin and worldwide are threatened by development pressures and thus the vital ecological role they play within freshwater systems must be urgently recognised and protected.