Groundwater Level Measurements Research Articles

Assessment of a Coastal Aquifer in the Framework of Conjunctive Use of Surface Water and Groundwater—The Case of the River Nestos Western Delta, NE Greece

This paper presents research regarding the assessment of the hydrogeological system of the River Nestos Western Delta, NE Greece, during the period of 2019. The procedure included the collection and analysis of relevant hydrological and hydrogeological data concerning the aquifer system of the study area. Specifically, groundwater level measurements and sampling were carried out in a monitoring well network in the shallow unconfined and the deep confined aquifers of the study area, respectively; and surface water sampling was conducted from the River Nestos at selected locations in each of the main drainage canals, as well as in lagoons of the study area; followed by analysis and processing of the relevant chemical analyses results. Finally, piezometric, hydrochemical maps and diagrams were constructed to augment the evaluation of results and the assessment of the system. The present study contributes to the development and management of water resources in the River Nestos Delta area by providing insight into the hydrodynamic and hydrochemical status of the system based on comprehensive contemporary data that can support and justify the compilation of realistic measurements. The conjunctive management of the surface and groundwater in the study area can improve the quantitative and qualitative characteristics of the water. The water level in piezometric maps varies from −4 m up to 16 m for both time periods (May 2019 and October 2019). Moreover, the maximum values of EC are 2700 μS/cm and 2390 μS/cm for the confined and unconfined aquifer systems, respectively. The maximum values of Cl− concentrations are 573.89 mg/L for the confined aquifer system and 514.73 mg/L for the unconfined aquifer system for both time periods (May 2019 and October 2019).

On the representability of soil water samples in space and time: Impact of heterogeneous solute transport pathways underneath a sandy field

In Europe, millions of water samples have been collected from sampling points, especially in the saturated zone to assess the water quality among others to fulfil EU water quality directives. Often water samples are collected from sampling points installed in the subsurface without knowing what the water collected represents in space and time. As such, without detailed knowledge of hydrogeological settings and fluctuations in groundwater levels, it is not possible to assess whether water collected represents a hydraulic active sediment setting or an adjacent isolated sediment body. Collecting water from the latter will hence not reveal by analysis potential contamination in the hydraulic active setting. Based on a detailed three-dimensional sedimentary facies model interpreted from geological and geophysical data combined with groundwater level measurements, this study focuses on delineating the impact of changing solute transport pathways underneath a sandy field (2 ha) exposed to bromide and pesticide applications. Hence, the analyses utilize detections in water samples of bromide, pesticides, and/or their degradation products collected through 19 years at 25 sampling points. A special focus is on the relatively high concentration, long-termed leaching of four degradation products (1,2,4-triazole, CGA108906, PPU, and desethyl-terbuthylazine) through the field. The results show that even for sand, knowledge of the hydrogeological setting and in-situ fate knowledge is imperative to assess the representability of water being sampled from both the variably-saturated and saturated zone of the soil-sediment system. Especially, the sub-horizontal layered sediments with numerous facies shifts facilitate horizontal solute transport, and fluctuations in the groundwater table seem to be decisive for, which solute transport pathways are dominating. Such detailed insights are crucial for accurately assessing sources of contaminants, leaching risk of contaminants through the variably-saturated zone, and improving monitoring procedures in the protection of the water resources and hereby the water quality of the future.

Assessment of spatial and temporal variability of groundwater level in the aquifer system on the flanks of Mount Meru, Northern Tanzania

Study regionMount Meru located in Northern Tanzania. Study focusGroundwater level monitoring is essential for uncovering the spatial-temporal variation of groundwater levels in a studied aquifer, helping discussions on the sustainable use and management of groundwater resources. This study analyses the spatial and temporal variability of groundwater level in the shallow aquifer system on the flanks of Mount Meru. Time series analysis of groundwater level measurements obtained in two hydrologic years: 2018–2019 and 2019–2020 is applied. New hydrological insights for the regionOn the north-eastern flank of Mount Meru, at Ngarenanyuki, there is a rise of about 1.80 m between the static water levels in April 2018 and December 2020 in the shallow aquifer, whereas on the western flank, at Mamsa, there is a decrease of about 0.50 m between the static water levels in May 2018 and December 2020 in the shallow aquifer, this can be attributed to low/reduced recharge (due to very low hydraulic conductivity and semi-confined condition of the aquifer), or exploitation. Hence, the current pumping practices in the aquifer on the western flank should be restrained for sustainable groundwater management.

Temporal interpolation of groundwater level hydrographs for regional drought analysis using mixed models

Large-scale studies of the spatial and temporal variation of groundwater drought status require complete inventories of groundwater levels on regular time steps from many sites so that a standardised drought index can be calculated for each site. However, groundwater levels are often measured sporadically, and inventories include missing or erroneous data. A flexible and efficient modelling framework is developed to fill gaps and regularise data in such inventories. It uses linear mixed models to account for seasonal variation, long-term trends and responses to precipitation and temperature over different temporal scales. The only data required to estimate the models are the groundwater level measurements and freely available gridded weather products. The contribution of each of the four types of trends at a site can be determined and thus the causes of temporal variation of groundwater levels can be interpreted. Validation reveals that the models explain a substantial proportion of groundwater level variation and that the uncertainty of the predictions is accurately quantified. The computation for each site takes less than 130 s and requires little supervision. Hence, the approach is suitable to be upscaled to represent the variation of groundwater levels in large datasets consisting of thousands of boreholes.

Estimation of unrecorded groundwater abstractions in Jordan through regional groundwater modelling

Jordan suffers from water scarcity and groundwater covers the majority of Jordan’s water supply. Therefore, there is an urgent need to manage this resource conscientiously. A regional numerical groundwater flow model, developed as part of a decision support system for the country of Jordan, allows for quantification of the overexploitation of groundwater resources and enables determination of the extent of unrecorded agricultural groundwater abstraction. Groundwater in Jordan is abstracted from three main aquifers partly separated by aquitards. With updated geological, structural, and hydrogeological data available in the country, a regional numerical groundwater flow model for the whole of Jordan and the southernmost part of Syria was developed using MODFLOW. It was first calibrated for a steady-state condition using data from the 1960s, when groundwater abstraction was negligible. After transient calibration using groundwater level measurements from all aquifers, model results reproduce the large groundwater-level declines experienced in the last decades, which have led to the drying out of numerous springs. They show a reversal of groundwater flow directions in some regions, due to over-abstraction, and demonstrate that documented abstractions are not sufficient to cause the observed groundwater-level decline. Only after considering irrigation water demand derived from remote sensing data, the model is able to simulate these declines. Illegal abstractions can be quantified and predictive scenarios show the potential impact of different management strategies on future groundwater resources.

Localizing Hydrological Drought Early Warning Using In Situ Groundwater Sensors

AbstractDrought early warning systems (DEWSs) aim to spatially monitor and forecast risk of water shortage to inform early, risk‐mitigating interventions. However, due to the scarcity of in situ monitoring in groundwater‐dependent arid zones, spatial drought exposure is inferred using maps of satellite‐based indicators such as rainfall anomalies, soil moisture, and vegetation indices. On the local scale, these coarse‐resolution proxy indicators provide a poor inference of groundwater availability. The improving affordability and technical capability of modern sensors significantly increases the feasibility of taking direct groundwater level measurements in data‐scarce, arid regions on a larger scale. Here, we assess the potential of in situ monitoring to provide a localized index of hydrological drought in Somaliland. We find that calibrating a lumped groundwater model with a short time series of groundwater level observations substantially improves the quantification of local water availability when compared to satellite‐based indices. By varying the calibration length, we find that a 5‐week period capturing both wet and dry season conditions provides most of the calibration capacity. This suggests that short monitoring campaigns are suitable for improving estimations of local water availabilities during drought. Short calibration periods have practical advantages, as the relocation of sensors enables rapid characterization of a large number of wells. These well simulations can supplement continuous in situ monitoring of strategic point sources to setup large‐scale monitoring systems with contextualized and localized information on water availability. This information can be used as early warning evidence for the financing and targeting of early actions to mitigate impacts of hydrological drought.

Analyzing urbanization induced groundwater stress and land deformation using time-series Sentinel-1 datasets applying PSInSAR approach

Urban intensification has taken a serious toll on the groundwater reserves which is one of the primary sources of fresh water on earth. Exploitation of groundwater has exponentially increased over time, especially in urban landscapes, with ever increasing demands to cater the growing population and development processes. This emphasizes on the importance of proper monitoring of the groundwater variations, which is a difficult process for not being directly accessible for physical measurements. Therefore, it is essential to develop advanced innovative indirect methods to help long-term monitoring of groundwater reserves at a relatively higher resolution, so that local level variations and their impact could be studied in case of excessively exploited zones, like cities. Recent studies have linked land-subsidence to over-exploitation of groundwater, which can be critical for urban scenario, which requires longer duration for replenishment. Thus, this study focuses on monitoring of the groundwater variations using time-series Sentinel-1 Interferometric SAR (InSAR) datasets by retrieving land deformation by PsInSAR (Persistent Scatterer Interferometric SAR) technique; applying phase information of permanent scattering candidates. 58 and 60 images were acquired during ascending and descending passes respectively between 9/10/2014 to 2/7/2020 for the study area i.e., Lucknow city (India) and its surroundings. The field measurements of groundwater level for various seasons (pre and post monsoons) were acquired from the Central Groundwater Board, Government of India (CGWB). Besides, Landsat 5 and 8 datasets were utilized to analyze the pattern of urban growth for a 30-year period and predict the near future scenario. In-depth analysis of all the components revealed a direct relationship between land deformation, groundwater variations and urban expansion. A high correlation coefficient of 0.886 was observed between groundwater level variation and the retrieved deformation measured along the groundwater wells along the deformation zones. Therefore, the overall analysis and results indicate that PsInSAR technique has great potential for estimating the groundwater levels and surface deformation at higher resolution and could be easily applied for any other city for continuous assessment.

Impact of Mountain Reservoir Construction on Groundwater Level in Downstream Loess Areas in Guanzhong Basin, China

An accurate understanding of the relationship between reservoir construction and the dynamic change of groundwater level in downstream areas is of great significance for rational development and utilization of water resources. At present, the research on the interaction between surface water (SW) and groundwater (GW) mainly focuses on the interaction between river and GW. There are few studies on the impact of the reservoir construction on GW level in downstream loess irrigation area. Rainfall, evaporation and climate temperature have a great impact on W level, but the impact of reservoir construction on the GW level should not be ignored in the utilization of water resources. In this paper, a GW flow model under a natural boundary was established by numerical simulation. Taking Heihe Jinpen Reservoir in Heihe River watershed as the research object, the influence of the construction of a mountain reservoir on the dynamic change of GW level in the downstream loess region is studied. By comparing the GW level under the natural state without reservoir construction and the measured GW level after the reservoir was built, the variation of the GW depth in the loess area of the lower reaches in the Heihe River watershed is obtained. The results show that simulation accuracy of the interaction between SW and GW was reasonable; after the Heihe Jinpen Reservoir construction, the mean GW level decrease was about 6.05 m in the downstream loess irrigation area in Guanzhong Basin. It provides a method for the simulation and prediction of SW–GW conversion laws. This study is also of great significance to explore the change law of the water cycle and improve the utilization rate of water resources.

From Dynamic Groundwater Level Measurements to Regional Aquifer Parameters— Assessing the Power of Spectral Analysis

AbstractLarge‐scale groundwater models are required to estimate groundwater availability and to inform water management strategies on the national scale. However, parameterization of large‐scale groundwater models covering areas of major river basins and more is challenging due to the lack of observational data and the mismatch between the scales of modeling and measurements. In this work, we propose to bridge the scale gap and derive regional hydraulic parameters by spectral analysis of groundwater level fluctuations. We hypothesize that specific locations in aquifers can reveal regional parameters of the hydraulic system. We first generate ensembles of synthetic but realistic aquifers which systematically differ in complexity. Applying Liang and Zhang’s (2013), https://doi.org/10.1016/j.jhydrol.2012.11.044, semi‐analytical solution for the spectrum of hydraulic head time series, we identify for each ensemble member and at different locations representative aquifer parameters. Next, we extend our study to investigate the use of spectral analysis in more complex numerical models and in real settings. Our analyses indicate that the variance of inferred effective transmissivity and storativity values for stochastic aquifer ensembles is small for observation points which are far away from the Dirichlet boundary. Moreover, the head time series has to cover a period which is roughly 10 times as long as the characteristic time of the aquifer. In deterministic aquifer models we infer equivalent, regionally valid parameters. A sensitivity analysis further reveals that as long as the aquifer length and the position of the groundwater measurement location is roughly known, the parameters can be robustly estimated.

Assessment of natural groundwater reserve of a morphodynamic system using an information-based model in a part of Ganga basin, Northern India

Assessment of morphodynamic groundwater reserves is important for the sustainable management of water resources. It is a truth that groundwater resource evaluation is anxious with the ambiguity of its several factors and employing methods. Thus, an information-based model has been hypothesized to assess natural groundwater reserves in a morphodynamic system in a part of the Ganga basin of Northern India, where the spatial variability in natural groundwater reserve exists. Marginal information of rainfall data, and transinformation among the rainfall, and monthly depth to groundwater level measurement at 50 wells in a dense monitoring network were used for evaluating natural groundwater reserve. The results indicate that an average recharge rate is about 246 mm/monsoon and or 32.65% of the seasonal rainfall, and its values are well-correlated with the soil infiltration rate. It has been found that the estimated recharge rates are about 54.08, 45.85, 33.77, 32.48, and 32.14% of the seasonal rainfall in an active flood plain, back swamp, natural levees, flood plain, and palaeochannel, respectively. The calculated annual rainfall input to groundwater reserve is found about 127.98 MCM/monsoon rainfall, which could be employed for sustainable management of groundwater resources in the morphodynamic system of the Ganga river basin.

Hydrogeophysical Inversion of Time‐Lapse ERT Data to Determine Hillslope Subsurface Hydraulic Properties

AbstractTime‐lapse electrical resistivity tomography (ERT) data are increasingly used to inform the hydrologic dynamics of mountainous environments at the hillslope scale. Despite their popularity and recent advancements in hydrogeophysical inversion methods, few studies have shown how time‐lapse ERT data can be used to determine hydraulic parameters of subsurface water flow models. This study uses synthetic and field‐collected, hillslope‐scale, time‐lapse ERT data to determine subsurface hydraulic properties of a two‐layer, physics‐based, 2‐D vertical flow model with predefined layer and boundary locations. Uncoupled and coupled hydrogeophysical inversion methods are combined with a fine‐earth fraction optimization scheme to reduce the number of parameters needing calibration and interpret the influence of the hydraulic parameters on the hydrologic model predictions. Inversions of synthetic ERT data recover the prescribed fine‐earth fraction bulk density to within 0.1 g cm−3. Field‐collected ERT data from a mountain hillslope result in hydrologic model dynamics that are consistent with previous studies and measured water content data but struggle to capture measured groundwater levels. The uncoupled hydrogeophysical inversion method is more sensitive to changes in hydraulic parameter values of the lower hydrologic model layer than the coupled hydrogeophysical inversion method. Time series of minimum objective function value simulations indicate that periodically collected ERT data may recover hydraulic parameters to a similar level of uncertainty as daily ERT data. Using simple hydrologic model domains within hydrogeophysical inversions shows promise for providing reasonable hydrologic predictions while maintaining relatively simple calibration schemes and should be explored further in future studies.

A relation for accelerating deformation of sandy soil and its application to predict the time to failure of a sandy model slope under repeated rainfall

The measurement of groundwater level and surface displacement in a sandy model slope under repeated rainfall was conducted to examine the effect of repeated pore pressure loading and unloading on the slope deformation. The velocity increased with small fluctuation even immediately before failure. Positive and negative accelerations occurred due to fluctuations in the velocity. The velocity increased with a considerable rise in the groundwater level and approached its ultimate value immediately before failure. The surface displacement increased not only with the rise in the groundwater level but also with the fall of the groundwater level and under a constant groundwater level. The relationships between the velocity and the absolute value of the acceleration derived from the surface displacement were linear on a logarithmic scale and unique for each stage with increasing and decreasing velocities due to the rise and lowering in the groundwater level. While the relationship was different during the stage of creep during failure. The relationship had been recognized to be applicable only during an increase in velocity; in this paper, a new relationship was established for any velocity trend and the method for predicting the time of failure was proposed based on the relationship between the velocity and acceleration. The time remaining to failure, which was defined as the difference between the predicted failure time and present time, could approach zero at the actual failure time when the constant α in the equation was greater than 1.4, and the determining factor in regression analysis for deriving the constant was high under different periods of measurement before the final event. The time remaining to failure approaching zero might be an indicator for predicting failure time.

Assessing Groundwater Dynamics and Hydrological Processes in the Sand River Deposits of the Limpopo River, Mozambique

Drought and water scarcity constrain the socioeconomic development of many (semi-)arid regions of Southern Africa. Moreover, due to the increase of water withdrawals upstream, the Limpopo River is no longer perennial in Mozambique. Fortunately, its river bed can store significant amounts of freshwater, because of the occurrence of thick and often coarse sand deposits formed through pronounced dryland weathering, erosion, and sedimentation in the river channel. Such so-called “sand rivers” exist in many parts of semi-arid Africa and have varying configurations and hydrological conditions. The current research aims to comparatively assess the Limpopo sand river aquifer in terms of recharge and discharge dynamics, storage potential, and interactions with the surface water flow, as a function of its specific hydrological conditions: its large size, location downstream of a dam releasing permanent ecological flow, and its relatively undeveloped state. For this purpose field investigations were carried out at two sites, involving groundwater level measurements, 2D geoelectrical surveying, water chemical and stable isotope analysis, and sediment classification. These investigations reveal the occurrence of medium to coarse sands with thicknesses that can reach 10–15 m, dropping to 2–5 m in the main river channel, underlain by less permeable clays and silts. Analysis of the river level shows that large parts of the sand river are flooded almost every year, providing optimal conditions for recurring and rapid recharge of the system (confirmed by infiltration tests) through two mechanisms: direct infiltration of surface runoff and lateral flow toward non-flooded areas of the river valley, also confirmed by the chemical and isotope study. During the dry season, groundwater provides base flow to the river and the average water level drop in the sand river system is about 1.8 m. The connectivity with the river margins is limited, due to the clayey nature of the river bank sediment, but local paleochannels can result in a continuation of sand layers. Hydrological processes controlling the water quality are evapoconcentration, mixing of discharging groundwater with the perennial surface water flow, and to a minor extent mineral dissolution, with the groundwater being of Ca-HCO3 type. The combination of the large size, high permeability, and frequent flooding of the sand river deposits provides optimal conditions for groundwater abstraction, requiring additional assessment of the impact on riparian vegetation and downstream users.

Citizen Science and the Sustainable Development Goals: Building Social and Technical Capacity through Data Collection in the Upper Blue Nile Basin, Ethiopia

Engaging youth and women in data-scarce, least developed countries (LDCs) is gaining attention in the Sustainable Development Goal (SDG) arena, as is using citizen science as a multi-faceted mechanism for data collection, engendering personal empowerment and agency. Involving these populations in citizen science is a powerful synergy that simultaneously addresses the Leave-No-One-Behind promise in the United Nations’ 2030 Agenda, yet most citizen science takes place in the Global North, and attention to LDCs is needed. This article highlights a four-year, four-location, hydrology-focused, interdisciplinary citizen science initiative (CSI) in the Upper Blue Nile Basin, Ethiopia. Through a systematic evaluation, we explore scientific applications of the hydrologic data, as well as the social dimensions in the CSI, towards building a social and technical capacity that supports the SDGs at the local and international scale. In the CSI, Ethiopian high school students received training from local university faculty and graduate students, collecting river stage and groundwater level measurements, and farmers conducted soil resistivity measurements using a novel sensor technology developed for the study area. We found the datasets to be ample for use to locally validate regional groundwater models and seasonal forecasts on soil moisture and streamflow. We conducted written interviews with the students, which revealed their ability to perceive benefits of engagement in the CSI, as well as recognize their increased individual technical capacity. An analysis of the hydrological data demonstrates the readiness of the datasets to be used for evaluating water-related interventions that facilitate the SDGs, broadly, by building synergies between individuals and institutions. As such, we map how both the hydrologic data and experiences of the citizen scientists support the SDGs at the Goal and Target-level, while forging new social and technical pathways.

GROUNDWATER HYDROGEOLOGY: STUDY CASE ON MANGANESE ORE EX-MINING OPENING HOLE AT KLIRIPAN, KULONPROGO REGENCY

The study was conducted in the opening hole of the former manganese ore mining of Vertical Shaft (PTPM) and Inclined Shaft (Sunoto) located in Dusun Kliripan, Desa Hargorejo, Kecamatan Kokap, Kabupaten Kulonprogo, Provinsi Daerah Istimewa Yogyakarta. The two planned openings will be the object of geological tourism and underground mining practice of mining engineering students. This research wants to study the hydrogeological conditions in the Dusun Kliripan. The methods used in this research are literature study, field orientation, primary data collection including measurement of groundwater level and infiltration rate, as well as the topography of the study area, secondary data include rainfall data, topographic maps, geological maps, and hydrogeological maps. The next stage includes data processing, as well as the study of data processing results. The results obtained were lithology conditions including Frozen Rock, Volcanic Breccia, and Limestone, the average infiltration rate obtained was 0.16 cm/min, and the groundwater level in the Kliripan at an elevation of 70 masl to 92 masl, with basin groundwater included in the Menoreh Groundwater Basin area. The Kliripan area has a sufficiently good groundwater reserve with complete hydrogeological elements so that it can be used for continued use of groundwater in the region.

Improving the Accuracy of Groundwater Storage Estimates Based on Groundwater Weighted Fusion Model

It is an effective measure to estimate groundwater storage anomalies (GWSA) by combining Gravity Recovery and Climate Experiment (GRACE) data and hydrological models. However, GWSA results based on a single hydrological model and GRACE data may have greater uncertainties, and it is difficult to verify in some regions where in situ groundwater-level measurements are limited. First, to solve this problem, a groundwater weighted fusion model (GWFM) is presented, based on the extended triple collocation (ETC) method. Second, the Shiyang River Basin (SYRB) is taken as an example, and in situ groundwater-level measurements are used to evaluate the performance of the GWFM. The comparison indicates that the correlation coefficient (CC) and Nash-Sutcliffe efficiency coefficient (NSE) are increased by 9–40% and 23–657%, respectively, relative to the original results. Moreover, the root mean squared error (RMSE) is reduced by 9–28%, which verifies the superiority of the GWFM. Third, the spatiotemporal distribution and influencing factors of GWSA in the Hexi Corridor (HC) are comprehensively analyzed during the period between 2003 and 2016. The results show that GWSA decline, with a trend of −2.37 ± 0.38 mm/yr from 2003 to 2010, and the downward trend after 2011 (−0.46 ± 1.35 mm/yr) slow down significantly compared to 2003–2010. The spatial distribution obtained by the GWFM is more reliable compared to the arithmetic average results, and GWFM-based GWSA fully retain the advantages of different models, especially in the southeastern part of the SYRB. Additionally, a simple index is used to evaluate the contributions of climatic factors and human factors to groundwater storage (GWS) in the HC and its different subregions. The index indicates that climate factors occupy a dominant position in the SLRB and SYRB, while human factors have a significant impact on GWS in the Heihe River Basin (HRB). This study can provide suggestions for the management and assessments of groundwater resources in some arid regions.

Geophysical investigations in the Radovna River Spring area (Julian Alps, NW Slovenia)

vodeAbstractThe Radovna River Valley is located in the north-western part of Slovenia in the Julian Alps, where there is an extensive intergranular aquifer whose depth to pre-Quaternary bedrock is unknown. Therefore, to obtain information about the depth of the valley and the geometry of the aquifer two geophysical methods were used in our study; ground penetrating radar (GPR) and seismic reflection method. The low-frequency GPR method has shown to be useful for determining the depth of the groundwater and the predominant groundwater recharge. Also, the high-resolution seismic method provided an insight about the morphology of the pre-Quaternary basement with the deepest point at 141 meters below surface. Measurements of hydrogeological parameters such as groundwater level and river discharge measurements were carried out in the study area. Both data analyses showed that groundwater level and river discharge are highly fluctuating and rapidly changing, indicating a well-permeable aquifer, implying that such an aquifer is extremely sensitive and vulnerable to extreme climate events. Both the geophysical methods and the hydrogeological information have provided important information about the morphology of the valley and the alluvial aquifer, as well as increasing the knowledge about the Radovna springs system, which will contribute very important information for future hydrogeological studies.

The origin of Uranium in groundwater of the eastern Halkidiki region, northern Greece

Uranium (U) pollution in groundwater has become a serious problem worldwide. Even in low concentrations, U has both radiological and toxicological impacts on human health. In this study an integrated hydrogeological approach was applied to conceptualize an aquifer system, and determine the origin of U detected in the aquifer of the eastern Halkidiki region in northern Greece. Data from measurements of groundwater level and hydrochemical and stable isotope analyses of groundwater samples were applied to perform geochemical modeling and multivariate statistical analysis. The modeling and statistical analysis identified three hydrogeochemical groups within the studied hydro-system, and U(VI) as the dominant U species. The first group is linked to the deeper aquifer which is characterized by water-rock interactions with weathering products of granodiorite. In this group the dominant U species is uranyl phosphate and U concentration is 3.7 μg/L. The upper aquifer corresponds to the second hydrogeochemical group where U concentrations are mainly influenced by high concentrations of nitrogen species (NO3− and NO2−). Factor analysis further discriminated the upper aquifer into a saline coastal zone and an inland zone impacted by agricultural activities. The third hydrogeochemical group presents the highest concentration of U (up to 15 μg/L) in groundwater and corresponds to the internal aquifer system. The U within this system is triggered by the presence of Mn2+, while the long residence time of the groundwater contributes synergistically to the hydrogeochemical process. Manganese triggers U oxidation in parallel with Fe2+ precipitation that acts as a regulator of U concentration. Groundwater depletion of the upper aquifers promotes the up-coning of geothermal fluids from fault zones leading to increased concentrations of U in the mid-depth aquifers.

Water Dynamics in a Coastal Wetland in the “Parque Costero del Sur” Biosphere Reserve, Argentina

Interactions and exchanges between surface water, groundwater, and the atmosphere are some of the most relevant functions that regulate environmental characteristics in wetlands. These functions depend on environmental attributes such as topography, geological-geomorphological setting and, in the case of coastal wetlands, the relationship with tidal flows. The aim of this work is to analyse the water flows in different landscape units of the wetland in the coastal plain of the Río de la Plata estuary within the Parque Costero del Sur biosphere reserve. For this purpose, monthly water balances and groundwater level measurements were compared with daily precipitation and tidal height data from the Río de la Plata estuary. The results show how water dynamics in the wetland responds to different geological-geomorphological and climatic controls. The main inlets and outlets of water, as well as the flow exchanges, vary according to the different landscape units, forming a complex system on which the main ecological features depend.

A decision support tool for optimising groundwater-level monitoring networks using an adaptive genetic algorithm

Abstract Mapping of the spatial variability of sparse groundwater-level measurements is usually achieved by means of geostatistical methods. This work tackles the problem of deficient sampling of an aquifer, by employing an innovative integer adaptive genetic algorithm (iaGA) coupled with geostatistical modelling by means of ordinary kriging, to optimise the monitoring network. Fitness functions based on three different errors are used for removing a constant number of boreholes from the monitoring network. The developed methodology has been applied to the Mires basin in Crete, Greece. The methodological improvement proposed concerns the adaptive method for the GA, which affects the crossover–mutation fractions depending on the stall parameter, aiming at higher accuracy and faster convergence of the GA. The initial dataset consists of 70 monitoring boreholes and the applied methodology shows that as many as 40 boreholes can be removed, while still retaining an accurate mapping of groundwater levels. The proposed scenario for optimising the monitoring network consists of removing 30 boreholes, in which case the estimated uncertainty is considerably smaller. A sensitivity analysis is conducted to compare the performance of the standard GA with the proposed iaGA. The integrated methodology presented is easily replicable for other areas for efficient monitoring networks design.