Nitrogen (N) pollution in shallow groundwater within the Jianghan Plain—a depositional basin along the Yangtze River in China—is a serious issue affecting the local water supply. There is little concern regarding temporal variation patterns of groundwater N in regions with intensive groundwater/surface-water interactions thus far. In this study, a 2-year field monitoring program and a set of incubation experiments were jointly applied to characterize the seasonal variation mechanisms of groundwater N. Groundwater monitoring suggested that temporal N variations in monitoring wells of 25 and 10-m depth were correlated with fluctuations in water levels, with lower NH₄-N and higher NO₃⁻-N concentrations corresponding to groundwater discharge during the dry season, and with higher NH₄-N and lower NO₃⁻-N concentrations corresponding to groundwater recharge during the wet season. Batch sediment incubation experiments showed that buried organic carbon in sediments from the field site could not promote NH₄-N release, but exogenous organic carbon and oxidant input could catalyze organic N mineralization, resulting in NH₄-N release. Nevertheless, NO₃⁻-N release was limited in all incubations. Thus, the temporal variation patterns could be divided into (1) groundwater N in type-1 wells (25 and 10 m), controlled by the annual reversal of groundwater flow gradient, which determined whether there was input of exogenous organic carbon or oxidants, ultimately affecting organic N mineralization, denitrification and other transformation processes, and (2) groundwater N in type-2 wells (<4 m depth), which showed no significant seasonal variation, implying the process is mainly controlled by surface inputs in the shallower subsurface.

Infiltration usually plays a significant role in construction failures and transfer of contaminants. Therefore, it is very important to monitor underground water migration. In this study, a soil infiltration experiment was carried out using an indoor model test. The water infiltration characteristics were recorded and analyzed based on the response of the geoelectric field, including the primary field potential, self-potential, excitation current and apparent resistivity. The phreatic water surface and the infiltration velocity were determined. The inversion results were compared with direct observations. The results showed that the changes in the geoelectric field parameters explain the principles of groundwater flow. The infiltration velocity and the phreatic surface can be determined based on the primary field potential response and the excitation current. When the phreatic surface reached the location of the electrodes, the primary field potential and self-potential decreased rapidly whereas the excitation current increased rapidly. The height of the phreatic surface and the infiltration time exhibited a linear relationship for both the observation data and the calculations of the excitation current. The apparent resistivity described the infiltration status in the soil and tracked the phreatic surface accurately.

The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m³/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.

In the Gran Sasso fissured carbonate aquifer (central Italy), a long-term (2001–2007) spatio-temporal hydrochemical and²²²Rn tracing survey was performed with the goal to investigate groundwater flow and water–rock interaction. Analyses of the physico-chemical parameters, and comparisons of multichemical and characteristic ratios in space and time, and subsequent statistical analyses, permitted a characterisation of the hydrogeology. At the regional scale, groundwater flows from recharge areas to the springs located at the aquifer boundaries, with a gradual increase of mineralisation and temperature along its flowpaths. However, the parameters of each group of springs may significantly deviate from the regional trend owing to fast flows and to the geological setting of the discharge spring areas, as corroborated by statistical data. Along regional flowpaths, the effects of seasonal recharge and lowering of the water table clearly cause changes in ion concentrations over time. This conceptual model was validated by an analysis of the²²²Rn content in groundwater.²²²Rn content, for which temporal variability depends on seasonal fluctuations of the water table, local lithology and the fracture network at the spring discharge areas, was considered as a tracer of the final stages of groundwater flowpaths.

Travel time is one of the important criteria in the design of managed aquifer recharge systems for securing good drinking water quality. Traditionally, groundwater travel time has been modelled without considering the effect of temperature. In this study, a cross-sectional heat transport model was constructed for the Amsterdam dune filtration system (in the Netherlands) to analyse the effect of temperature on groundwater travel times. A groundwater flow model, a chloride transport model, and a heat transport model were iteratively calibrated with measured groundwater levels, chloride concentrations, and temperature series in order to improve model calibration and reduce model uncertainty. The coupled flow and heat transport model with temperature-dependent density and viscosity provided more accurate estimation of travel times. The results show that seasonal temperature fluctuations in the source water in the infiltration pond cause temperature variations in the shallow groundwater. Viscosity is more sensitive to temperature changes and has a larger effect on groundwater travel times. Groundwater travel time in the shallow sand aquifer increases from 60 days when computed with the traditional groundwater flow model to 73 days in the winter season and 95 days in the summer season when computed with the coupled model. Longer travel time is beneficial for water quality improvement. Thus, it is important to consider the effect of temperature variations on groundwater travel times for the design and operation of managed aquifer recharge systems.

Mandalay is a major city in central Myanmar with a high urban population and which lacks a central wastewater management system, a solid waste disposal process, and access to treated drinking water. The purpose of this study is to investigate the groundwater quality of local dug wells and tube wells, determine quantitative data on characteristics of the Amarapura Aquifer, and compare seasonal variations in groundwater flow and quality. Water samples were collected during the dry and wet seasons, then analyzed for major ion chemistry using ion chromatography to identify indicators of wastewater contamination transport to the shallow aquifer and to compare seasonal variations in groundwater chemistry. An open-source analytic element model, GFLOW, was used to describe the physical hydrogeology and to determine groundwater flow characteristics in the aquifer. Hydrogeochemistry data and numerical groundwater flow models provide evidence that the Amarapura Aquifer is susceptible to contamination from anthropogenic sources. The dominant water types in most dug wells and tube wells is Na-Cl, but there is no known geologic source of NaCl near Mandalay. Many of these wells also contain water with high electrical conductivity, chloride, nitrate, ammonium, and E. coli. Physical measurements and GFLOW characterize groundwater flow directions predominantly towards the Irrawaddy River and with average linear velocities ranging from 1.76 × 10⁻² m/day (2.04 × 10⁻⁷ m/s) to 9.25 m/day (1.07 × 10⁻⁴ m/s). This is the first hydrogeological characterization conducted in Myanmar.

Identification and quantification of groundwater and surface-water interactions provide important scientific insights for managing groundwater and surface-water conjunctively. This is especially relevant in semi-arid areas where groundwater is often the main source to feed river discharge and to maintain groundwater dependent ecosystems. Multiple field measurements were taken in the semi-arid Bulang sub-catchment, part of the Hailiutu River basin in northwest China, to identify and quantify groundwater and surface-water interactions. Measurements of groundwater levels and stream stages for a 1-year investigation period indicate continuous groundwater discharge to the river. Temperature measurements of stream water, streambed deposits at different depths, and groundwater confirm the upward flow of groundwater to the stream during all seasons. Results of a tracer-based hydrograph separation exercise reveal that, even during heavy rainfall events, groundwater contributes much more to the increased stream discharge than direct surface runoff. Spatially distributed groundwater seepage along the stream was estimated using mass balance equations with electrical conductivity measurements during a constant salt injection experiment. Calculated groundwater seepage rates showed surprisingly large spatial variations for a relatively homogeneous sandy aquifer.

The Agua Amarga coastal aquifer has experienced different anthropic interventions over the last 100 years. Since 2008, groundwater abstractions along the coastline to supply the Alicante I and II desalination plants have been combined with artificial recharge. This measure, consisting of seawater irrigation over the salt marsh, has reduced the impact on the piezometry and surface ecosystems. The study of the effect of this measure on groundwater flow is addressed by applying an inverse problem protocol to temperature profiles monitored in a piezometer located inside the recharge area. Information on monthly seawater irrigation volumes, rainfall, and average air and seawater temperatures have also been gathered as input data to quantify vertical flow. An upward flow component for the period 2010–2022 that varies between 2 × 10⁻⁹ and 7.5 × 10⁻⁷ m/s has been found. These values decrease near the surface, where the flow is mainly horizontal.

A groundwater flow model of the Alpine valley aquifer in the Aosta Plain (NW Italy) showed that well pumping can induce river streamflow depletions as a function of well location. Analysis of the water budget showed that ∼80% of the water pumped during 2 years by a selected well in the downstream area comes from the baseflow of the main river discharge. Alluvial aquifers hosted in Alpine valleys fall within a particular hydrogeological context where groundwater/surface-water relationships change from upstream to downstream as well as seasonally. A transient groundwater model using MODFLOW2005 and the Streamflow-Routing (SFR2) Package is here presented, aimed at investigating water exchanges between the main regional river (Dora Baltea River, a left-hand tributary of the Po River), its tributaries and the underlying shallow aquifer, which is affected by seasonal oscillations. The three-dimensional distribution of the hydraulic conductivity of the aquifer was obtained by means of a specific coding system within the database TANGRAM. Both head and flux targets were used to perform the model calibration using PEST. Results showed that the fluctuations of the water table play an important role in groundwater/surface-water interconnections. In upstream areas, groundwater is recharged by water leaking through the riverbed and the well abstraction component of the water budget changes as a function of the hydraulic conditions of the aquifer. In downstream areas, groundwater is drained by the river and most of the water pumped by wells comes from the base flow component of the river discharge.

Understanding the response of groundwater levels in alluvial and sedimentary basin aquifers to climatic variability and human water-resource developments is a key step in many hydrogeological investigations. This study presents an analysis of groundwater response to climate variability from 2000 to 2012 in the Queensland part of the sedimentary Clarence-Moreton Basin, Australia. It contributes to the baseline hydrogeological understanding by identifying the primary groundwater flow pattern, water-level response to climate extremes, and the resulting dynamics of surface-water/groundwater interaction. Groundwater-level measurements from thousands of bores over several decades were analysed using Kriging and nonparametric trend analysis, together with a newly developed three-dimensional geological model. Groundwater-level contours suggest that groundwater flow in the shallow aquifers shows local variations in the close vicinity of streams, notwithstanding general conformance with topographic relief. The trend analysis reveals that climate variability can be quickly reflected in the shallow aquifers of the Clarence-Moreton Basin although the alluvial aquifers have a quicker rainfall response than the sedimentary bedrock formations. The Lockyer Valley alluvium represents the most sensitively responding alluvium in the area, with the highest declining (−0.7 m/year) and ascending (2.1 m/year) Sen’s slope rates during and after the drought period, respectively. Different surface-water/groundwater interaction characteristics were observed in different catchments by studying groundwater-level fluctuations along hydrogeologic cross-sections. The findings of this study lay a foundation for future water-resource management in the study area.