Studying Hydraulic Interconnections in Low-Permeability Media by Using Bacterial Communities as Natural Tracers

Abstract

Knowledge about the processes governing subsurface microbial dynamics in and to groundwater represents an important tool for the development of robust, evidence-based policies and strategies to assess the potential impact of contamination sources and for the implementation of appropriate land use and management practices. In this research, we assessed the effectiveness of using microorganisms as natural tracers to analyze subsurface dynamics in a low-permeability system of northern Italy. Microbial communities were investigated through next-generation sequencing of 16S rRNA gene both to study hydraulic interconnections in clayey media and to verify the efficacy of outcropping clayey horizons in protecting groundwater against contamination. During the observation period, a rapid water percolation from the ground surface to the saturated medium was observed, and the mixing between lower-salinity fresh-infiltration waters and higher-salinity groundwater determined the formation of a halocline. This rapid percolation was a driver for the transport of microorganisms from the topsoil to the subsurface, as demonstrated by the presence of soil and rhizosphere bacteria in groundwater. Some of the species detected can carry out important processes such as denitrification or nitrate-reduction, whereas some others are known human pathogens (Legionella pneumophila and Legionella feeleii). These findings could be of utmost importance when studying the evolution of nitrate contamination over space and time in those areas where agricultural, industrial, and civil activities have significantly increased the levels of reactive nitrogen (N) in water bodies but, at the same time, could highlight that groundwater vulnerability of confined or semi-confined aquifers against contamination (both chemical and microbiological) could be higher than expected.

Hydrogeological Behaviour and Geochemical Features of Waters in Evaporite-Bearing Low-Permeability Successions: A Case Study in Southern Sicily, Italy

“…Microbial communities are influenced by the physicochemical features of the environment in which they live and are excellent investigative tools in several hydrogeological scenarios. The efficacy of using microorganisms for specific hydrogeological purposes has been verified in several settings that are partially comparable with that addressed in this study, such as karstified media (e.g., [30,31]), low-permeability media (e.g., [32,33]), and high-salinity groundwaters (e.g., [34]).…”

Processes and factors controlling the groundwater flow in a complex landslide: A case study in the northern Italy

“…Also in literature (e.g., de Montety et al, 2007; Di Maio et al, 2015) anomalous high concentrations of Na + and SO 4 2− are related with the most active zones of landslide. Even if no mineralogical data coming from the slip surface in the test site are available, soil samples collected at different depths in the landslide mass from two boreholes close to the upper and the lower cluster respectively, show the presence of significant amounts of quartz, discrete quantities of clay materials (illite, chlorite and irregular mixed layers illite‐smectite and illite‐chlorite) and subordinate plagioclase (Rizzo et al, 2020). It is well known (e.g., Castro et al, 2020) that slope failure usually involves structural changes and that these modifications can lead to changes in chemo‐mechanical properties, generally increasing the concentration of clay minerals.…”

Microbiome characterization of alpine water springs for human consumption reveals site- and usage-specific microbial signatures

“…While there is a general consensus on the fact that groundwater environments are quite stable in terms of physico-chemical parameters ( Griebler and Lueders, 2009 ), flora and fauna ( Cantonati et al, 2006 ), the composition of microbial communities seems to vary according to several parameters such as EC, discharge ( Yan et al, 2021 ), and temperature and pH ( Power et al, 2018 ). A number of studies suggest that the microbiome can be used as a tracer for water quality in such environments, microbiological tracers have been effective in detecting hydraulic interconnection ( Rizzo et al, 2020 ), seawater intrusion ( Hernàndez-Diaz et al, 2019 ), and seismic events in SPA settings ( Valeriani et al, 2020 ). Therefore the knowledge of spatial and temporal community dynamics is fundamental for both conservation issues and for the management of the ecosystem services provided by the water springs.…”