Abstract

In aquatic ecosystems, the biomass, activity and composition of microorganisms are determined to a large extent by local and regional environmental conditions. While karst aquifers are an important source for drinking water, the ecology of microbial communities in karst waters has hardly been studied. This study examined the regional variations and seasonal dynamics of microbial communities in pristine karst spring waters of Slovenia (Central Europe). Fifteen springs distributed across 5 eco-regions exhibiting a strong altitudinal gradient were sampled 4 times a year. Evaluation of the microbial communities included quantification of prokaryotic biomass via total cell counts and microbial activity estimated via measurements of electron transport system activity. The taxonomic structure of the bacterial communities was analysed by terminal restriction fragment length polymorphism fingerprinting. Biological measures were complemented by a set of physico-chemical parameters, including dissolved organic carbon, nutrients, major ions, temperature, electrical conductivity, pH, and dissolved oxygen. Bacterial community structure differed significantly with seasons and eco-regions, with the latter causing greater variation. While the overall power of the environmental variable tested was a moderate factor (15%) in explaining the variability in microbial community structure, catchment altitude was a key determinant. Prokaryotic cell density and microbial activity in spring water decreased with an increase in catchment altitude and were significantly positively correlated. For a better understanding of karst ecosystems and the ecosystem service of water purification, future investigation should address karst microbial communities at a higher phylogenetic and functional resolution.

Highlights

  • Groundwater from karst aquifers supplies a quarter of the world’s population with drinking water (Smart & Worthington 2004a)

  • We investigated spatio-temporal dynamics of prokaryotic cell numbers, microbial respiratory activity, and bacterial community structure from 15 karst springs that belong to geographically distinct aquifers in 5 eco-regions of Slovenia (Central Europe)

  • Most of the studies on groundwater microbial communities have addressed contaminated aquifers, with only a few that looked at pristine groundwater ecosystems, and even fewer into karst aquifers

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Summary

Introduction

Groundwater from karst aquifers supplies a quarter of the world’s population with drinking water (Smart & Worthington 2004a). Aquat Microb Ecol 86: 99–114, 2021 system services such as water purification processes through the mineralisation of carbon and other nutrients (Griebler & Avramov 2015). Microbial communities are discharged with karst water to the surface, making them accessible for detailed analysis (Smart & Worthington 2004b). Karst springs, even when used to supply drinking water, are regularly monitored only for (1) the quantity of discharge, (2) basic physico-chemical parameters (temperature, pH, electrical conductivity [EC], dissolved oxygen [DO], major ions, and nutrients), (3) specific groups of chemicals (e.g. pesticides), and (4) the presence of indicators for faecal contamination (E. coli and coliform bacteria). Our knowledge about the microbiology of karst aquifers and springs is rather limited (Farnleitner et al 2005, Pronk et al 2009, Wilhartitz et al 2009, Shabarova et al 2014), including the Slovenian karst

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