Microorganisms as contaminants and natural tracers: a 10-year research in some carbonate aquifers (southern Italy)

Abstract

Limestone aquifers provide the main drinking water resources of southern Italy. Due to cattle grazing and/or manure spreading, these aquifers are often characterized by microbial contamination of groundwater. The aim of this paper is to summarize the results obtained during a 10-year research carried out in experimental field sites in southern Italy, analyzing (1) the influence of the topsoil of pyroclastic origin on the migration of microbial cells from the ground towards the groundwater, and then on the groundwater vulnerability, (2) the influence of the rainfall regime on the breakthrough at the springs, (3) the reliability of thermotolerant coliforms and fecal enterococci as bacterial indicators of microbial contamination, and (4) the effectiveness of microorganisms as natural tracers for some hydrogeological purposes. The results obtained showed that fecal enterococci are a more reliable indicator than thermotolerant coliforms for detecting contamination and that the entity and distribution over time of microbial contamination of fecal origin are influenced by several factors, such as precipitation regime, thermal regime and existence and thickness of the topsoil of pyroclastic origin. Moreover, the migration of a significant amount of bacterial cells through the topsoil and the underlying carbonate rocks allows the utilization of microorganisms as effective natural tracers, to be coupled with other classic tracers to study the recharge and the flow processes. In a broader perspective, these results can be used to optimize the investigations in other hydrogeological scenarios, with emphasis on those where different water types coexist and interact in same aquifer systems

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]).…”

Integrating Hydrogeological and Microbiological Data and Modelling to Characterize the Hydraulic Features and Behaviour of Coastal Carbonate Aquifers: A Case in Western Cuba

“…Since bacteria are abundant, ubiquitous and thrive even in extreme habitats, microbiological investigations together with hydrogeological, geochemical, isotopic, and geophysical investigations can represent a valuable tool for studying aquifer system behaviour [10]. Interesting results have been obtained in carbonate environments of southern Italy, where the potential use of microorganisms as tracers in hydrogeological studies has been assessed regarding the analysis of recharge and flow processes, and in hypersaline and hydrothermal systems as well [10,11]. These achievements have been possible thanks to the development and application of molecular biological methods in the field of hydrogeology that have permitted increasing numbers of studies pertaining to microbial communities of aquifer systems.…”

“…Several methods have been employed to reveal microbial community composition and responses to environmental changes in many environments and in different contexts [10,11,[19][20][21][22]. An understanding of the temporal and spatial structures, functions, interactions and population dynamics of microbial communities is critical for many aspects of life, including sustainable agriculture, environmental protection and human health [23].…”

Use of Molecular Markers to Compare Escherichia coli Transport with Traditional Groundwater Tracers in Epikarst

“…Breakthrough curves (BTCs) can also show differing behaviors between tracers, as seen in an epikarst trace in which a solute had a broader BTC than bacteriophages (Flynn and Sinreich, 2010). Not only can differences in cell size and surface characteristics influence transport (Becker et al, 2003; Flynn and Sinreich, 2010; Cook et al, 2011; Bucci et al, 2015), but composition of the substrate itself (e.g., presence of metal oxides) (Bolster et al, 2006) and hydrochemical conditions (Chen and Walker, 2007; Flynn and Sinreich, 2010) can affect attenuation of microorganisms. Size and distribution of pores and fissures (causing straining of particulates), antecedent moisture conditions, and presence of biofilms in epikarst can all influence tracer behavior (Sinreich et al, 2009; Wang et al, 2011).…”

“…Differing transport behaviors and attenuation have been observed between various microorganisms in both column tests and groundwater traces (Bolster et al, 2006; Flynn and Sinreich, 2010; Magal et al, 2013; Hillebrand et al, 2012, 2015; Mudarra et al, 2014; Bucci et al, 2015). Differences between strains of the same bacteria (including surface charge, capsular formation, and exopolysaccharide composition) can also influence adhesion and transport capabilities.…”