A multiparameter analysis of environmental gradients related to hydrological conditions in a binary karst system (underground course of the Pivka River, Slovenia)

Abstract

A multiparameter analysis of environmental gradients related to hydrological conditions in a binary karst system (underground course of the Pivka River, Slovenia) Chemical and bacterial gradients under different hydrological conditions were studied in a well-developed underground karst system. Water samples were collected from the main underground drainage conduit of the Pivka River from October 2013 until June 2016. The system responds quickly to external pulses (precipitation events), and is also impacted by human interventions, as is demonstrated mainly by fluctuations of sulphates, chlorides, and occasionally elevated concentrations of organic and faecal pollutants. Chemical and bacterial parameters showed a monotonous trend of decreasing concentrations from the ponor towards the interior of the karst massif during stable hydrological conditions, and a significant change during high water conditions. High flow events tend to equilibrate chemical and bacterial parameters in the underground river. Concentrations of chlorides, TOC (total organic carbon) and nitrates were the most indicative parameters describing the formation of the gradient. Stable isotopes of hydrogen and oxygen in water indicated that the main karst conduit collects isotopically different waters from the aquifer. The river water collected

Extremophilic Microorganisms in Central Europe

“…Anthropogenic influences can also change the physicochemical properties of these habitats and their microbial composition, as was shown for the Krajcarca spring in Triglav National Park, in Slovenia [79]. In the underground karst system of the Pivka River in Slovenia, human interventions correlate with fluctuations in the sulphate and chloride levels and the concentrations of organic and faecal pollutants [31].…”

“…Geochemical gradients of dissolved oxygen and sulphide can form ecotones where specialized archaeal and bacterial taxonomic groups thrive, depending on their metabolic and ecological requirements. Chemolithotrophic metabolism sustains the ecosystems of diverse bacterial and archaeal communities in oxygen-sulphide ecotones [26][27][28][29][30][31][32]. However, there remains a gap in our knowledge of microeukaryote diversity and their ecology in these redox-stratified habitats [33].…”

“…Caves and subsurface environments represent refugia and are sometimes windows into the past, thus providing suitable microbiomes for studying evolutionary biology [24] and studying intra-terrestrial microbial communities that have adapted to oligotrophic and cold conditions [25]. Underground karst systems with natural accessibility, such as the underground Pivka River, provide excellent study sites to monitor the quantitative changes of chemical and biological factors [31].…”

Antimicrobial resistant Escherichia coli from karst waters, surfaces and bat guano in Slovenian caves

“…The Pivka River (and Črni potok to a minor extent) is the main allogenic recharge for the Postojnski jamski sistem (Postojna Cave System, 45°46ʹ57˝N, 14°12ʹ13˝E, 529 m a.s.l., total length 24 km), which comprises several caves (Postojnska jama, Otoška jama, Magdalena jama, Pivka jama, Črna jama), where the underground Pivka River is accessible and collects isotopically different waters from the aquifer. The underground Pivka River is impacted by human activities within the surrounding area, as is indicated by occasionally elevated concentrations of sulphates, chlorides, and organic and faecal pollutants (Mulec et al 2019). In the underground it continues towards Planinska jama, where it converges with the Rak cave stream.…”

“…1). This can be attributed to a gradual die-off of bacteria along the underground course, but dilution with other waters within the karst aquifer cannot be excluded (Mulec et al 2019). In addition, the successful dissemination of E. coli and other epidemiologically important microbes depends upon environmental factors.…”