Data-Driven Modelling of Water Table Oscillations for a Porous Aquifer Occasionally Flowing under Pressure

Modelling of shallow porous aquifers in scenarios where boundary conditions change over time can be a difficult task. In particular, this is true when data modelling is pursued, i.e., models are directly constructed by measured data. In fact, data contain not only the information related to the physical phenomenon under investigation, but also the effects of time-varying boundary conditions, which work as a disturbance. This undesired component conditions the training of data-driven models, as they are fitted by models, which can produce predictions diverging from measured data. Here, a very shallow porous aquifer is modelled in terms of its response to water table to precipitation. The aquifer is characterized by the presence of a low permeability silty top layer covering the lower sandy strata, where the aquifer normally flows. Therefore, when the piezometric level increases up to the low permeability layer, the aquifer changes its behavior from phreatic to confined. This determines the changing boundary condition, which makes the response of the aquifer to rain precipitations complex, as it is related to a two-fold condition: confined or phreatic. The aquifer here is investigated by two machine learning approaches, the earlier based on an evolutionary modeling, and the latter based on artificial neural networks. Evolutionary modeling returned explicit equations with a fitness efficiency up to 0.8 for 1 month for predictions and 0.48 for simulations, while neural networks arrived at 0.85 and 0.28, respectively. The aim of this study is to get an explicit model of the response of the piezometric heights of the aquifer to the precipitations, which is useful for planning the use of groundwater resources.

Application of Visual MODFLOW to the Analysis of Boundary Conditions for a Phreatic Porous Aquifer Using Limited Available Information: A Case Study

The increasing water demand, especially in developing regions, continuously puts pressure on groundwater resources both quantitatively and qualitatively. Hydrogeological modeling is a tool used in planning and management of groundwater resources. The factors that interfere in groundwater flow dynamics can be determined by developing a conceptual model and they can be validated via a numerical model. The objective of the manuscript is the hydrogeological groundwater flow modeling of the phreatic porous aquifer of the Ribeirão Candidópolis catchment in the Itabira municipality, State of Minas Gerais (Brazil). The software used in this study is GMS: MODFLOW, which enabled a steady state flow regime modeling by means of the Finite Difference Method (FDM) and the parameters calibration from a semi-transient approach. To assess the performance of the model, the Mean Error (ME), the Mean Absolute Error (MAE), and the Root Mean Square Error (RMSE) were calculated. The results proved to be compatible with the values observed in the field. After several adjustments of the boundary conditions, a Normalized Root Mean Square (NRMS) of 9.648% and a correlation coefficient of 0.993 were obtained. Despite the economic importance of the study area, studies made available on groundwater flow behavior are rare. The results obtained via modeling are in accordance with the data observed in the field and consequently our model can be used in the study of water level changes.

Examining Plasmid Transfer of pJP4 in a Mixed Community Biofilm Formed in a Microcosm Simulating a Porous Aquifer

In this work, a lab-scale microcosm was designed and used to simulate a porous groundwater aquifer. A minimal media acted as the non-selective pressure for plasmid transfer, while a minimal media with gentamicin acted as the selective pressure. PCR, plate counts and confocal laser scanning microscopy were used to monitor transconjugant and donor persistence in the microcosm. The donor was identified through

Examining Plasmid Transfer of pJP4 in a Mixed Community Biofilm Formed in a Microcosm Simulating a Porous Aquifer

In this work, a lab-scale microcosm was designed and used to simulate a porous groundwater aquifer. A minimal media acted as the non-selective pressure for plasmid transfer, while a minimal media with gentamicin acted as the selective pressure. PCR, plate counts and confocal laser scanning microscopy were used to monitor transconjugant and donor persistence in the microcosm. The donor was identified through

Excess of sulfate and dissolved inorganic carbon in groundwaters fueled by pyrite oxidation and organic matter loads – A multi-isotope approach

<p>The biogeochemistry of sulfur and carbon in groundwater of a Quaternary porous aquifer system and associated surface (lake) waters was investigated to identify processes of water mixing and the sources of dissolved sulfate and dissolved inorganic carbon (DIC). The study area is situated in North-Eastern Germany (Mecklenburg-Western Pomerania) close to the Baltic Sea coastline. The area is under impact by agricultural activity on a regional scale. A major goal was to identify the natural and anthropogenic key hydrobiogeochemical processes controlling the coupled element cycles upon groundwater development. Besides major and minor elements, redox-sensitive trace elements, nutrients, and stable mulit-isotope signatures (H, C, O, S) were considered.</p><p>While water isotopes of most groundwaters are positioned on the meteoric water line, surface waters are affected by an evaporation-induced enrichment of heavy isotopes. These shifts allow for a quantification of mixing proportions in influenced groundwater wells between direct precipitation-derived groundwater and  infiltrating lake water born fractions.</p><p>Major element hydrochemical and the carbon isotope composition of DIC indicate soil CO<sub>2</sub> and the subterrestrial dissolution of carbonate minerals within the aquifer matrix as primary sources for DIC. Furthermore, contributions from oxidized dissolved organic carbon (DOC) under water-saturated conditions are found.</p><p>The coupled sulfur and oxygen isotope composition of dissolved sulfate indicates an origin dominatly  from the subterrestrial oxidation of iron sulfides, mainly pyrite. These iron sulfides are found in the sediments making the modern porous aquifer, in the study area with a deduced sulfur isotope composition of about -12 per mil vs. VCDT. These findings coupled to enhanced loads in dissolved iron and manganese, but low nutrient concentrations indicate nitrate as an important driver for lithoautothrophic pyrite oxidation. At several sites, the enhanced sulfate loads led to dissimilatory sulfate reduction and, thereby, to in-situ transformation of DOC (and/or Methane) to DIC. The enhancements of sulfate and DIC seems to be a typical feature in North German younger groundwaters and strongly (in)directly impacted by anthropogenic forces.</p>

Vertical Electrical Sounding (VES) for Estimation of Hydraulic Parameters in the Porous Aquifer

Similarities in both water and electric current flows allow the relation of hydraulic and geoelectric parameters of porous aquifers. Based on this assumption and the importance of the hydraulic parameters for groundwater analyses, this study aimed to estimate hydraulic conductivity (K) and transmissivity (T) with vertical electrical sounding (VES) in the porous aquifer at the experimental farm of the University of Brasilia, Brazil. VES is a geophysical technique that provides electrical resistivity (ρ, Ω m) and thickness (h) of the subsurface layers. The ρ and h aquifer data, associated with lithology, water table level (WTL), and groundwater electrical resistivity (ρw, Ω m), allowed the calculation of complementary geoelectric parameters (formation factor, F, and Dar Zarrouk parameters) and the relation with K and T, determined via slug test. VES data allowed the elaboration of geoelectric models, with mean absolute percentage error (MAPE) below 6% compared to field data, and the identification of the aquifer in each VES station. Significant exponential regression models (R2 > 0.5 and p-value < 0.05) showed the possibility of using geoelectric parameters to estimate hydraulic parameters. This study allowed the verification of the applicability of consolidated models and the identification of appropriate empirical relationships for hydrogeological characterization in the Brazilian tropical porous aquifers. The results of this work, besides the rapid sampling and low cost of performing vertical electrical sounding (VES), may justify the use of this geophysical technique for preliminary porous aquifer characterization, especially in regions absent of or with insufficient monitoring wells.

Hydrogeological and Hydrochemical Regime Evaluation in Flamouria Basin in Edessa (Northern Greece)

Groundwater quality deterioration and overexploitation constitute two critical environmental issues worldwide. In this study, with the aim to achieve a groundwater sustainability purpose, a preliminary hydrogeochemical survey is conducted in the Flamouria basin, Pella prefecture, Northern Greece using available and collected data. For this purpose, chemical analyses of groundwater, springs, and surface water were collected and analyzed with three electrical resistivity tomographies (ERTs). A Groundwater Quality Index (GQI), along with a nitrate susceptibility assessment is applied within the porous aquifer. The water quality analysis along with GQI application showed excellent water quality for potable and irrigation use however highlighted future issue for irrigation utilization as the high alkalinity and total dissolved solid (TDS)could generate excessive soil salinization. Moreover, the application of a methodology for the identification of “Nitrate Vulnerable Zone” called the Protection from Natural and Anthropogenic sources (PNA) highlighted the natural susceptibility to nitrate pollution of the porous aquifer, especially in the central part of the area where most agricultural activity is localized. The work further confirmed how the proposed elaboration could represent an easy and widely applicable hydrological assessment where there is also limited data available.