Groundwater is a hidden global keystone ecosystem.

Groundwater is a vital ecosystem of the global water cycle, hosting unique biodiversity and providing essential services to societies. Despite being the largest unfrozen freshwater resource, in a period of depletion by extraction and pollution, groundwater environments have been repeatedly overlooked in global biodiversity conservation agendas. Disregarding the importance of groundwater as an ecosystem ignores its critical role in preserving surface biomes. To foster timely global conservation of groundwater, we propose elevating the concept of keystone species into the realm of ecosystems, claiming groundwater as a keystone ecosystem that influences the integrity of many dependent ecosystems. Our global analysis shows that over half of land surface areas (52.6%) has a medium-to-high interaction with groundwater, reaching up to 74.9% when deserts and high mountains are excluded. We postulate that the intrinsic transboundary features of groundwater are critical for shifting perspectives towards more holistic approaches in aquatic ecology and beyond. Furthermore, we propose eight key themes to develop a science-policy integrated groundwater conservation agenda. Given ecosystems above and below the ground intersect at many levels, considering groundwater as an essential component of planetary health is pivotal to reduce biodiversity loss and buffer against climate change.

Vermiremediation applied to PCB and PCDD/F contaminated soils and its implications for percolating water.

PCDD/Fs (polychlorinated dibenzo-p-dioxins/dibenzofurans) and PCBs (polychlorinated biphenyls) are ubiquitous persistent pollutants with reduced bioavailability, which bioremediation using soil fauna is still managed to treat. This research set out to: (i) study the suitability of earthworms (Eisenia fetida), alone and associated with plants (Lepidium sativum), for the decontamination of PCDD/F and PCB polluted soils in Brescia-Caffaro (Italy), at total and congener concentration levels; (ii) simulate the action of earthworms in groundwater contamination process and nutrient mobility. Five treatments were set up: (i) uncontaminated soil with E. fetida (NC); (ii) contaminated soil (C); (iii) contaminated soil with E. fetida (CEf); (iv) contaminated soil with L. sativum (CLs); (v) contaminated soil with E. fetida and L. sativum (CEfLs). PCBs and PCDD/Fs in the soil prior to testing were measured. Analysis was repeated in soil treatments and percolating water at the end of the test period (4 months). Dissolved nutrient concentrations were measured in percolated water. PCB and PCDD/F concentrations, initially 259333.33 ± 10867.89 ng/kg and 176 ± 10.69 ngTE/kg, were significantly reduced after 4 months in all treatments. Treatments did not differ in total PCBs concentration (from 160,000 ng/kg to 194,000 ng/kg), but CEfLs congeners concentrations were less environmentally threatening; CEf and CLs resulted in lower PCDD/Fs concentration (79.43 ± 3.34 ngTE/kg and 73.03 ± 4.09 ngTE/kg, respectively). The action of earthworms could enhance contaminants and soluble reactive phosphorous content in percolating water.

Winter survival of microbial contaminants in soil: an in situ verification.

The aim of the research was to evaluate, at site scale, the influence of freezing and freeze/thaw cycles on the survival of faecal coliforms and faecal enterococci in soil, in a climate change perspective. Before the winter period and during grazing, viable cells of faecal coliforms and faecal enterococci were detected only in the first 10 cm below ground, while, after the winter period and before the new seasonal grazing, a lower number of viable cells of both faecal indicators was detected only in some of the investigated soil profiles, and within the first 5 cm. Taking into consideration the results of specific investigations, we hypothesise that the non-uniform spatial distribution of grass roots within the studied soil can play an important role in influencing this phenomenon, while several abiotic factors do not play any significant role. Taking into account the local trend in the increase of air temperature, a different distribution of microbial pollution over time is expected in spring waters, in future climate scenarios. The progressive increase in air temperature will cause a progressive decrease in freeze/thaw cycles at higher altitudes, minimising cold shocks on microbial cells, and causing spring water pollution also during winter.

Investigating the migration of immiscible contaminant fluid flow in homogeneous and heterogeneous aquifers with high-precision numerical simulations.

Numerical modeling of the migration of three-phase immiscible fluid flow in variably saturated zones is challenging due to the different behavior of the system between unsaturated and saturated zones. This behavior results in the use of different numerical methods for the numerical simulation of the fluid flow depending on whether it is in the unsaturated or saturated zones. This paper shows that using a high-resolution shock-capturing conservative method to resolve the nonlinear governing coupled partial differential equations of a three-phase immiscible fluid flow allows the numerical simulation of the system through both zones providing a unitary vision (and resolution) of the migration of an immiscible contaminant problem within a porous medium. In particular, using different initial scenarios (including impermeable "lenses" in heterogeneous aquifers), three-dimensional numerical simulation results are presented on the temporal evolution of the contaminant migration following the saturation profiles of the three-phases fluids flow in variably saturated zones. It is considered either light nonaqueous phase liquid with a density less than the water, or dense nonaqueous phase liquid, which has densities greater than the water initially released in unsaturated dry soil. Our study shows that the fate of the migration of immiscible contaminants in variably saturated zones can be accurately described, using a unique mathematical conservative model, with different evolution depending on the value of the system's physical parameters, including the contaminant density, and accurately tracking the evolution of the sharp (shock) contaminant front.

How do turbidite systems behave from the hydrogeological point of view? New insights and open questions coming from an interdisciplinary work in southern Italy.

Turbidite successions can behave either as aquitards or aquifers depending on their lithological and hydraulic features. In particular, post-depositional processes can increase rock permeability due to fracture development in the competent layers. Thus, at a local scale, turbidite systems warrant further detailed investigations, aimed at reconstructing reliable hydrogeological models. The objective of this work was to investigate from the hydrogeological perspective a turbiditic aquifer located in southern Italy, where several perennial and seasonal springs were detected. Considering the complex hydrodynamics of these systems at the catchment scale, to reach an optimal characterization, a multidisciplinary approach was adopted. The conceptual framework employed microbial communities as groundwater tracers, together with the physicochemical features and isotopic signature of springs and streams from water samples. Meanwhile, geophysical investigations coupled with the geological survey provided the contextualization of the hydrogeological data into the detailed geological reconstruction of the study area. This modus operandi allowed us to typify several differences among the samples, allowing identification of sources and paths of surface water and groundwater, along with diffuse groundwater outflow along streams. As a final result, a hydrogeological conceptual model was reconstructed, underlining how at a very local scale the lithologic, hydraulic, and geomorphological heterogeneity of the studied relief can lead to an improved hydrogeological conceptual model compared to that of other turbidite systems. These results open new questions about the hydrogeological behavior of turbiditic aquifers, which could be pivotal in future research. In fact, these systems could support relevant ecosystems and anthropic activities, especially where climate change will force the research of new (and probably less hydrogeologically efficient) water sources.

High-resolution shock-capturing numerical simulations of three-phase immiscible fluids from the unsaturated to the saturated zone.

Numerical modeling of immiscible contaminant fluid flow in unsaturated and saturated porous aquifers is of great importance in many scientific fields to properly manage groundwater resources. We present a high-resolution numerical model that simulates three-phase immiscible fluid flow in both unsaturated and saturated zone in a porous aquifer. We use coupled conserved mass equations for each phase and study the dynamics of a multiphase fluid flow as a function of saturation, capillary pressure, permeability, and porosity of the different phases, initial and boundary conditions. To deal with the sharp front originated from the partial differential equations' nonlinearity and accurately propagate the sharp front of the fluid component, we use a high-resolution shock-capturing method to treat discontinuities due to capillary pressure and permeabilities that depend on the saturation of the three different phases. The main approach to the problem's numerical solution is based on (full) explicit evolution of the discretized (in-space) variables. Since explicit methods require the time step to be sufficiently small, this condition is very restrictive, particularly for long-time integrations. With the increased computational speed and capacity of today's multicore computer, it is possible to simulate in detail contaminants' fate flow using high-performance computing.

Assessment of groundwater vulnerability using genetic algorithm and random forest methods (case study: Miandoab plain, NW of Iran).

One of the appropriate ways to prevent groundwater contamination is identifying the vulnerable areas of the aquifers. The DRASTIC framework, for assessing the intrinsic vulnerability of the aquifer, is a common method which uses a specific parameter's weight and a uniform distributed contaminant in overall the aquifer. Therefore, it should be calibrated for specific aquifer and contaminant distribution conditions. In this research, random forest (RF) and genetic algorithm (GA) methods were used for DRASTIC framework optimization in Miandoab plain (NW of Iran). In optimizing the basic DRASTIC framework (BDF) using GA, decision variables are the weight of DRASTIC parameters and weight values for each data layer are the outputs of the optimization. The final optimized map (BDF-GA map) was obtained using overlaying the layers with optimized weights based on the GA method. In optimization of BDF using RF, the model is made up of from 1 to 100 trees and the m parameter or split variables was optimized by changing the number of variables between one and the maximum variables of each subset. Also, the feature selection method is used to reduce the dimensions and increase the accuracy of the model. To induct the nitrate contaminant model, raster layer data of 7 BDF parameters, together with the target variable (VI of BDF map), were used. In the final step, variables' importance was identified by the RF method and then, the vulnerability map was obtained based on variable importance. In validation and comparison of methods with CI and ROC methods, the BDF-RF method with the higher CI and ROC values was ranked as the most accurate approach in groundwater vulnerability evaluation. The optimized map using the RF method (BDF-RF map) showed that 14.5, 13, 18, 26.5, and 28% of the plain are located in areas with very low, low, moderate, high, and very high vulnerability categories, respectively.

Groundwater quality assessment for different uses using various water quality indices in semi-arid region of central Tunisia.

The Hajeb Layoun-Jelma basin, located in the central Tunisia, is the principal source of water supply for Sidi Bouzid and Sfax region. The over-abstraction from this groundwater, since 1970, and the intensive agriculture activities led to the degradation of the water quantity and quality. The quality evaluation for this groundwater is very important tool for sustainable development and decision for water management. A total of 28 groundwater samples, from shallow, springs, and deep aquifers, were collected, storage and analyzed to evaluate its quality suitability for domestic and agriculture purposes using geographic information system and geochemical methods. For the both aquifers, the abundance of cations: Na > Mg > Ca > K, and of anions in the order: Cl > HCO3 > SO4. The dominant hydrochemical facies, for the shallow aquifer and springs, are Na-Cl and Ca-Mg-Cl; for the deep aquifer, the geochemical facies are Na-Cl, Ca-Mg-Cl, and Ca-Cl. The comparison of the major parameters and the chemical data with the World Health Organization standards and the national standards indicate that this groundwater is suitable for drinking, except in some samples, with high salinity concentrations. The water quality was assessed, for drinking uses, using "water quality index," "entropy," and "improved water quality index." The results mentioned that the improved water quality index is the best method which indicated that the poor water quality coincide with the Na-Cl water type. The entropy method and the water quality index present the optimistic methods. The irrigation suitability assessment was made using various parameters (SAR, TH, % Na, PI, MH, KR, EC). The results revealed that the majority of samples in Hajeb Layoun-Jelma basin are not appropriate for irrigation uses.

Potential role of Bacillus endospores in soil amended by olive mill wastewater.

The main aim of this work was to know how spread is laccase activity in spores of Bacillus species isolated from a soil where Italian law allows olive mill wastewater (OMW) spreading, and to investigate the potential role of such autochthonous soil microorganisms in degradation of OMW phenols, and prevention of groundwater pollution. Laccase activity was detected for the first time in spores of wild-type Bacillus pumilus, B. cereus sensu lato, and B. amyloliquefaciens strains. Because B. pumilus, B. cereus sensu lato, and B. amyloliquefaciens, together with B. subtilis account for a total of 93% of Bacillus isolates at the study site, the nearly totality of Bacillus spores reveals laccase activity. Thus, taking also into consideration that Bacillus spores are more abundant (about 100-fold) than white-rot fungi (that possess a well known extracellular, radical-based ligninolytic enzyme system capable of degrading OMW phenols) in the studied soil, these spores may contribute to in-situ degradation of OMW phenols. This role is further emphasized by dilution of crude OMW during infiltration of rainwater through soil that allows to minimize the antibacterial activity of phenols. The widespread presence of Bacillus spores in soils indicates a potential detoxifying role of these spores in a broader context.

A Python Script to Compute Isochrones for MODFLOW.

MODFLOW constitutes today the most popular modeling tool in the study of water flow in aquifers and in modeling aquifers. To simplify the interface to MODFLOW various GUI have been developed for the creation of model definition files and for the visualization and interpretation of results. Recently Bakker et al. (2016) developed the FloPy interface to MODFLOW that allows to import and use the produced simulation data using Python. This allows to construct model input files, run the models, read and plot simulations results through Python scripts. In this note, we present a Python program (that uses FloPy) interface that allows us to generate time-related capture zones (isochrones) for confined 2D steady-state groundwater flow in unbounded domains, with one or more wells. As an application, we show a validation of the approach and the results of four basic test cases: a homogenous aquifer with one well, a heterogeneous aquifer with one well, an aquifer with four wells located both longitudinal and perpendicular to the flow direction.

A global review on ambient Limestone-Precipitating Springs (LPS): Hydrogeological setting, ecology, and conservation.

Springs are biodiversity hotspots and unique habitats that are threatened, especially by water overdraft. Here we review knowledge on ambient-temperature (non-geothermal) freshwater springs that achieve sufficient oversaturation for CaCO3 -by physical CO2 degassing and activity of photoautotrophs- to deposit limestone, locally resulting in scenic carbonate structures: Limestone-Precipitating Springs (LPS). The most characteristic organisms in these springs are those that contribute to carbonate precipitation, e.g.: the mosses Palustriella and Eucladium, the crenophilous desmid Oocardium stratum, and cyanobacteria (e.g., Rivularia). These organisms appear to be sensitive to phosphorus pollution. Invertebrate diversity is modest, and highest in pools with an aquatic-terrestrial interface. Internationally, comprehensive legislation for spring protection is still relatively scarce. Where available, it covers all spring types. The situation in Europe is peculiar: the only widespread spring type included in the EU Habitat Directive is LPS, mainly because of landscape aesthetics. To support LPS inventorying and management to meet conservation-legislation requirements we developed a general conceptual model to predict where LPS are more likely to occur. The model is based on the pre-requisites for LPS: an aquifer lithology that enables build-up of high bicarbonate and Ca(2+) to sustain CaCO3 oversaturation after spring emergence, combined with intense groundwater percolation especially along structural discontinuities (e.g., fault zones, joints, schistosity), and a proper hydrogeological structure of the discharging area. We validated this model by means of the LPS information system for the Emilia-Romagna Region (northern Italy). The main threats to LPS are water diversion, nutrient enrichment, and lack of awareness by non-specialized persons and administrators. We discuss an emblematic case study to provide management suggestions. The present review is devoted to LPS but the output of intense ecological research in Central Europe during the past decades has clearly shown that effective conservation legislation should be urgently extended to comprise all types of spring habitats.

Filtration of Bacillus subtilis and Bacillus cereus spores in a pyroclastic topsoil, carbonate Apennines, southern Italy.

A comparative study on the filtration of Bacillus subtilis and Bacillus cereus spores in a pyroclastic topsoil was performed in laboratory using surfactant-free solutions and solutions with the surfactant sodium dodecyl sulphate (SDS) (anionic). The results of the column experiments demonstrate that the SDS does not significantly influence the retention of both B. subtilis and B. cereus spores. Since the SDS is adsorbed through hydrophobic interaction with the organic matter of soil media, these results suggest that hydrophobic interaction between spores and organic matter does not play a significant role on filtration processes within the studied topsoil. This statement is of utmost importance taking into consideration the hydrophobic nature of Bacillus spores and the very high organic matter content in the studied topsoil (20-34%). Conversely, the retention of the analyzed spores seems to be influenced by the pore size exclusion phenomenon.

Role of organic matter and clay fraction on migration of Escherichia coli cells through pyroclastic soils, southern Italy.

A comparative study on the adsorption of Escherichia coli cells to two different pyroclastic soils collected in southern Italy (carbonate Apennines) was performed in laboratory using surfactant-free solutions and solutions with the surfactants sodium dodecyl sulphate (SDS, anionic) and octylphenoxypolyethoxyethanol (Triton X-100, non-ionic). Both soils are rich in organic matter (up to 35%), but only one contains a clay fraction (2-5%). The experiments demonstrated that E. coli cells are significantly adsorbed to the clay fraction of the soil, while the organic matter content does not play a significant role. The pore size exclusion phenomenon is another factor to consider when analyzing the retention of E. coli cells within such soils. However, despite the existence of different factors that enhance bacterial cells retention, a high percent of E. coli cells is transported through soil media. The not absolute protection of such soils against microbial pollution is supported not only by the results of the column experiments at lab scale, but also by the findings of a field monitoring at site scale.

Influence of precipitation and soil on transport of fecal enterococci in fractured limestone aquifers.

Limestone aquifers provide the main drinking water resources of southern Italy. The groundwater is often contaminated by fecal bacteria because of the interaction between rocks having high permeability and microbial pollutants introduced into the environment by grazing and/or manure spreading. The microbial contamination of springwater in picnic areas located in high mountains can cause gastrointestinal illness. This study was carried out in order to analyze the interaction between Enterococcus faecalis and the soil of a limestone aquifer and to verify the influence of this interaction on the time dependence of groundwater contamination. E. faecalis was chosen because, in the study area involved, it represents a better indicator than Escherichia coli. The research was carried out through field (springwater monitoring) and laboratory experiments (column tests with intact soil blocks). The transport of bacterial cells through soil samples was analyzed by simulating an infiltration event that was monitored in the study area. Comparison of laboratory results with data acquired in the field showed that discontinuous precipitation caused an intermittent migration of microorganisms through the soil and produced, together with dispersion in the fractured medium (unsaturated and saturated zones), an articulated breakthrough at the spring. The short distances of bacterial transport in the study area produced a significant daily variability of bacterial contamination at the field scale.