What we can learn about transboundary aquifers from geochemical signatures of springs

As groundwater does not follow human-drawn boundaries such as country borders, groundwater pollution in one country can adversely affect groundwater quality and availability in a neighboring country. It is vital to develop a conceptual understanding of shared groundwater resources not only to ensure their protection, but also to avoid future conflicts, especially in a changing climate. Both the Water Convention and EU Water Framework Directive emphasize the need for joint assessment and management of transboundary groundwater resources (commonly referred to as “transboundary aquifers” or “groundwater bodies''), and it is crucial to establish a representative transboundary groundwater monitoring network to gather the necessary data. Often, the coverage of monitoring points in the existing groundwater monitoring networks is scarce in the peripheral areas and the installation of new wells would be economically unreasonable. Springs are natural groundwater outflows that can fill gaps in monitoring networks. Monitoring springs can be cost-effective, make water sampling easier, moreover, their water can provide information on a significantly larger catchment area than monitoring wells. The spring site cannot be selected like monitoring wells, so selecting the best springs requires a thorough preliminary assessment. A good conceptual understanding of the recharge area is a prerequisite for the selection of suitable monitoring springs. In this study, 46 springs in the transboundary area of Estonia and Latvia (NE Europe) were screened in 2021-2022 for a variety of geochemical parameters (field parameters, major ions, biogenic and trace elements, water stable isotopes). Some springs were sampled more than once to assess seasonal variability. Then springs were clustered based on their geochemical characteristics using multivariate statistics. This study is the first step in the procedure established on how to select representative springs for transboundary aquifer monitoring.

This study is financed by the Interreg Estonia-Latvia cooperation program project “WaterAct”, the EEA and Norway Grants Fund for Regional Cooperation project “EU-WATERRES”, and by performance-based funding of University of Latvia Nr.AAP2016/B041 within the “Climate change and sustainable use of natural resources” program.