Saltwater intrusion in Denmark

The studies investigating saltwater intrusion in Denmark have been reviewed to identify the main characteristics and features that have an impact on coastal aquifers interacting with the sea. Traditionally, in regions with wet climate, saltwater intrusion is not appointed as a frequent problem and it is more commonly linked to areas affected by water scarcity. Nevertheless, multiple factors that can induce the salinization of coastal aquifers have been found for Denmark such as the presence of coastal drained lowlands with the water table below the sea level or karstic features and buried valleys in carbonate and detrital systems respectively that can act as preferential flow paths for saline water. Eustatic changes have been also played an important role in the salinization of aquifers, in deep aquifers saline ancient connate water can be identified and in small islands, a delicate equilibrium of freshwater lenses is generated over saline water. As the water supply in this country depends almost exclusively on groundwater, saltwater intrusion can jeopardize fresh groundwater resources in coastal areas. An overview of the cases already studied, questions about the magnitude of these issues and the future perspectives with climate changes are discussed to put into context what is already known and what are the next challenges.Se han revisado los estudios que han investigado la intrusión marina en Dinamarca para identificar las principales características que afectan a los acuíferos costeros en su interacción con el mar. Tradicionalmente, en regiones con clima húmedo, la intrusión marina no es considerada como un problema frecuente ya que se suele asociar con áreas afectadas por la escasez de agua. Sin embargo, se han identificado múltiples factores que pueden generar la salinización de acuíferos costeros en Dinamarca como la presencia de tierras bajas drenadas a lo largo de la costa con niveles freáticos por debajo del nivel del mar o el flujo preferente a través de morfologías kársticas o paleovalles en acuíferos carbonatados o detríticos respectivamente. Los cambios eustáticos han jugado también un papel importante en la salinización de acuíferos, en acuíferos profundos se pueden llegar a identificar aguas connatas antiguas y en islas de reducido tamaño, se establece un delicado equilibrio con lentes de agua dulce sobre aguas salinas. Debido a que este país depende casi exclusivamente de las aguas subterráneas para el abastecimiento de la población, la intrusión marina podría poner en riesgo los recursos subterráneos de agua dulce en las zonas costeras. La revisión de casos estudiados plantea una serie de cuestiones acerca de la magnitud de los problemas existentes y las perspectivas futuras considerando cambios climáticos. Con esta revisión se ha puesto en contexto el estado actual de conocimiento acerca de la intrusión marina en el país y se han identificado los desafíos que podría ser necesario acometer en el futuroNext-Generation EU funding: Programa Maria Zambrano Senior MZSA0

Comparison of evapotranspiration estimates using the water balance and the eddy covariance methods

Abstract The eddy covariance method estimates the energy flux of latent heat for evapotranspiration. However, imbalance between the land surface energy output and input is a well‐known fact. Energy balance closure is most commonly not achieved, and therefore the eddy covariance method potentially underestimates actual evapotranspiration. Notwithstanding, the method is one of the most established measurement techniques for estimating evapotranspiration. Here, evapotranspiration from eddy covariance (ETEC) is cross‐checked with evapotranspiration calculated as the residual of the water balance (ETwb). The water balance closure using ETEC is simultaneously validated. Over a 6‐yr period, all major terms of the water balance are measured including precipitation, recharge from percolation lysimeters, and soil moisture content from a cosmic‐ray neutron sensor, a capacitance sensor network, and time domain reflectometry (TDR), respectively. In addition, we estimate their respective uncertainties. The study demonstrates that both monthly and yearly ETEC and ETwb compare well and that the water balance is closed when ETEC is used. Concurrently, incoming available energy (net radiation minus ground heat flux) on average exceeds the turbulent energy fluxes (latent heat flux and sensible heat flux) by 31%, exposing the energy–surface imbalance. Consequently, the imbalance in the energy balance using the eddy covariance method must, to a lesser degree, be caused by errors in the latent heat estimates but can mainly be attributed to errors in the other energy flux components