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.

Understanding the hydrological functioning of the scarce freshwater bodies of semiarid regions is crucial, especially in those areas affected by anthropic activities involving land-use changes. In the dry western edge of the Argentina Pampean plains, a system of more than 100 shallow lakes of remarkable stability occurs. These lakes exhibit low salinity compared to those located in the more humid belt. This system has constituted the main water resource for humans from prehispanic times to the present. Stable isotopes were used to establish the seasonal surface-water/groundwater interactions and the hydrological conditions in a lake of the Dry Pampean Plain (DPP), i.e., Lake Los Pocitos, to understand the mechanism that guarantees such a resource. Results indicate that evaporation mainly controls the isotopic composition of lake water, overwhelming the effect of higher rainfall inputs during the wet (but also most evaporative) season. The δ¹⁸O mass balance model indicates greater groundwater inflow to the lake during the dry season (~0.4 m month⁻¹) compared to the wet season (~0.2 m month⁻¹). Lake level decreased in the wet season due to the lowest groundwater inflow and the greatest evaporation rate. Based on the proportion of water entering a lake that leaves through evaporation, Los Pocitos corresponds to a throughflow lake with a short water residence time (~0.47 years). These hydrologic conditions, along with freshwater inputs from a dune located at the western margin of the lake, determine the existence of this relatively stable and freshwater lake in the DPP where high evaporation rates are registered.

The Badain Jaran Desert (BJD) in China is a desert with impressive sand dunes and a groundwater situation that has attracted numerous researchers. This paper gives an overview of the mysteries of groundwater in the BJD that are exhibited as five key problems identified in previous studies. These problems relate to the origin of the groundwater, the hydrological connection between the BJD and the Heihe River Basin (HRB), the infiltration recharge, the lake–groundwater interactions, and the features of stable isotope analyses. The existing controversial analyses and hypotheses have caused debate and have hindered effective water resources management in the region. In recent years, these problems have been partly addressed by additional surveys. It has been revealed that the Quaternary sandy sediments and Neogene-Cretaceous sandstones form a thick aquifer system in the BJD. Groundwater flow at the regional scale is dominated by a significant difference in water levels between the surrounding mountains and lowlands at the western and northern edges. Discharge of groundwater from the BJD to the downstream HRB occurs according to the regional flow. Seasonal fluctuations of the water level in lakes are less than 0.5 m due to the quasi-steady groundwater discharge. The magnitude of infiltration recharge is still highly uncertain because significant limitations existed in previous studies. The evaporation effect may be the key to interpreting the anomalous negative deuterium-excess in the BJD groundwater. Further investigations are expected to reveal the hydrogeological conditions in more detail.

Temperature distribution and heat transport are studied in a coastal aquifer at De Panne in the western Belgian coastal plain. Field observations include temperature profiles of groundwater in the dunes and temperature measurements at the water table in a profile on the shore. Freshwater–saltwater distribution is known from previous studies. These are used to constrain a density-dependent model simulating the freshwater–saltwater distribution and heat transport using the SEAWAT code. The yearly fluctuation of the groundwater temperature in the phreatic aquifer under the dunes, shore and sea, and the influence of a tidal inlet in the dunes are simulated. The observations show that seawater temperature variations determine the temperature variations on the shore whereas atmospheric temperature changes determine this in the dunes. Yearly temperature fluctuations imposed at the water table propagate mainly vertically in the aquifer with only limited lateral influence. Heat transport is mainly convection dominated. Thickness of the surficial zone is determined by the amplitude of the groundwater temperature at the water table and the groundwater flow. Establishment of a tidal inlet in the dunes results in asymmetric temperature profiles under and in the vicinity of it.