<p>Groundwater-surface water interactions are widespread across the globe and occur at the multiple interfaces across the landscape. These interactions, which involve the exchange of water and solutes, play a critical role in influencing water quality and ecosystems. While numerous studies have investigated the mechanisms of flow during groundwater-surface water exchanges, and the importance of these interactions has been recognized, it is now the time to highlight their impact on aquatic environment and ecosystems. In this topical collection, we invite manuscripts on topics including but not limited to (1) nutrient (carbon, nitrogen, phosphorus) cycle and contaminant transformation, transport and fate in the groundwater-surface water interaction zone; (2) the role of groundwater discharge on water quality or ecosystem structure of lakes, rivers, wetlands, and coastal environment, with emphasis on estimation of chemical fluxes; (3) the effects of surface water seepage on groundwater quality.</p>